An ultrananocrystalline twin rutile TiO2 thin film material with room-temperature ferroelectricity and a preparation method and application thereof
By growing ultra-dense nanotwinned rutile TiO2 films on Al2O3 substrates using pulsed laser deposition, the problem of introducing room-temperature ferroelectricity into rutile TiO2 was solved, achieving the preparation of high-performance TiO2 films and improving the efficiency of photocatalytic water splitting and material stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF METAL RESEARCH - CHINESE ACAD OF SCI
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-16
AI Technical Summary
Existing technologies struggle to introduce macroscopic and stable room-temperature ferroelectricity into rutile TiO2, and existing methods suffer from high preparation costs, poor material stability, and inconsistent performance.
Ultra-dense nanotwinned rutile TiO2 films were grown on Al2O3 substrates using pulsed laser deposition. By controlling the density and structure of the twin interface, TiO2 films with room-temperature ferroelectricity were prepared, with polarization along the in-plane direction, avoiding elemental doping and stress/strain introduction.
A TiO2 thin film with high residual polarization intensity was achieved, which improved the hydrogen production efficiency of photocatalytic water splitting, simplified the preparation process, made it suitable for large-scale production, and expanded the application range of TiO2.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of ferroelectric materials technology, specifically relating to an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity, its preparation method, and its application. Background Technology
[0002] Ferroelectric materials are a class of materials with reversible spontaneous polarization properties. Due to their enormous application potential and development prospects in ferroelectric random access memory (FeRAM), sensors, capacitors, and photocatalysis, they have consistently attracted high attention from the academic community. From the perspective of the formation mechanism of ferroelectricity, the electric dipoles constituting spontaneous polarization mainly originate from two sources: one is from the asymmetric distortion distribution of the electron cloud, typical systems such as LuFe2O4, PrCaMnO3, and Fe3O4; the other is from the relative displacement between ions, which is also the source of polarization in most ferroelectric materials, such as BaTiO3, PbTiO3, BiFeO3, HfO2, and YMnO3. Therefore, ferroelectricity is generally considered an intrinsic physical property closely related to the atomic and electronic structure of the crystal.
[0003] In recent years, two strategies for introducing ferroelectricity into non-ferroelectric materials have attracted widespread research interest. One strategy involves lowering the switching barrier of electric dipoles in piezoelectric materials through elemental doping. For example, recent studies have shown that doping AlN with B or Sc can exhibit significant ferroelectricity. However, this strategy has significant drawbacks: elemental doping alters the intrinsic physicochemical properties of the material, introducing harmful defects that lead to decreased material stability. Furthermore, the doping ratio is difficult to control precisely, increasing the complexity and cost of the fabrication process and hindering large-scale mass production. The other strategy utilizes the substrate effect of ferroelectric substrates to induce ferroelectric polarization in non-ferroelectric thin films. For instance, SrTiO3 films exhibit ferroelectricity under the influence of a PbTiO3 substrate. However, this method relies on a specific ferroelectric substrate, has a narrow applicability, and the induced ferroelectricity is mostly a localized effect, making it difficult to achieve macroscopic, stable, and tunable ferroelectric properties, thus failing to meet the application requirements of multi-size, high-quality ferroelectric functional materials.
[0004] Grain boundaries (GBs) are widely present in various materials. Recent studies have confirmed that in normally non-ferroelectric crystals, certain specific grain boundaries can produce localized polarity distortions, and even directly exhibit ferroelectricity. This theoretically proves that the unique symmetry and atomic arrangement at grain boundaries can form electric dipoles. However, a key scientific question remains: can these localized effects be precisely designed and thus translated into macroscopically controllable properties of materials?
[0005] Among various grain boundaries, twin boundaries (TBs) are characterized by simple structural units and low formation energy, making nanotwins widely used to modulate material properties. For example, by controlling the twin boundary density, significant breakthroughs have been achieved in optimizing the strength, plasticity, and hardness of nanotwinned metals and covalently bonded materials. Studies have also found that nanotwins can introduce ferrimagnetism into antiferromagnetic Cr₂O₃ films. Rutile titanium dioxide (R-TiO₂), as a classic semiconductor and photocatalytic material, has attracted considerable attention in the fields of solar-driven clean energy and electronic devices. Due to its centrosymmetric P₄² / mnm space group, R-TiO₂ is generally considered a nonferroelectric compound.
[0006] In recent years, researchers have conducted extensive studies on introducing ferroelectricity into rutile TiO2. Theoretically, ferroelectricity can be achieved through external pressure-induced phase transitions, as well as by controlling internal stress and strain to induce lattice distortion. Experimentally, ferroelectricity has been successfully achieved in rutile TiO2 through traditional stress / strain engineering and specific element doping. However, these methods all have insurmountable drawbacks: external pressure-induced phase transitions require complex high-pressure equipment, resulting in high preparation costs and difficulty in fabricating large-area, multi-size thin film materials; stress / strain engineering easily leads to cracks and defects in the film, affecting material stability and performance consistency; and element doping alters the intrinsic photocatalytic properties of rutile TiO2, increasing harmful defects and reducing its effectiveness in applications such as photocatalytic water splitting.
[0007] Furthermore, the {011} twin boundaries of rutile TiO2 have extremely low formation energy, and the Ti within the twin boundary structural units... 4+ The ions are significantly deviated from the center of the oxygen sublattice, which makes it possible to induce novel physical properties such as ferroelectricity in this system using nanotwins. However, in the current technology, no researchers have utilized this characteristic to introduce macroscopic and stable room-temperature ferroelectricity into rutile TiO2 by controlling the nanotwin structure. Therefore, developing a TiO2 ferroelectric material and its preparation method that is simple to process and stable without doping or stress / strain introduction has become an urgent technical problem to be solved in this field. Summary of the Invention
[0008] To address the problems existing in the prior art, the present invention aims to provide an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity and its preparation method. By performing appropriate pretreatment on the TiO2 substrate, the pulsed laser deposition process does not require pre-sputtering of the target surface. At the same time, by reasonably controlling the growth parameters of pulsed laser deposition, a TiO2 thin film with extremely high density {011} nanotwins is grown inside the film, thus preparing a TiO2 thin film with room temperature ferroelectricity. The ferroelectric polarization is along the in-plane direction and has high residual ferroelectric polarization. It can be used for photocatalytic water splitting, significantly improving hydrogen production efficiency.
[0009] The objective of this invention is achieved through the following technical solution:
[0010] In a first aspect, the present invention provides an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition. The rutile TiO2 ferroelectric thin film layer has ultra-dense nanotwins with a space group of P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, α=β=γ=90°. The ultra-dense nanotwinned rutile TiO2 thin film is polarized in three directions along the plane, with an angle of 120° between each direction.
[0011] Furthermore, the thickness of the rutile TiO2 ferroelectric thin film layer is 20nm-400nm;
[0012] Nanotwinned crystalline layers exist within the rutile TiO2 film in three 120° rotation variants. The thickness of the crystalline crystalline layers is 3-6 atomic layers. There is an excess of {011} twin interfaces in the rutile TiO2 film, and Ti at the twin interfaces is +4 valence.
[0013] Furthermore, the remanent polarization of the ultradense nanotwinned rutile TiO2 thin film material with room-temperature ferroelectricity is ≥27.2 μC / cm. 2 .
[0014] In a second aspect, the present invention provides a method for preparing an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity, comprising the following steps:
[0015] Pretreatment of Al2O3 substrate: The Al2O3 substrate is ultrasonically cleaned in an organic solvent to remove residual organic matter adhering to the substrate surface. Then the Al2O3 substrate is transferred to a vacuum growth chamber and heated for baking.
[0016] Preparation of TiO2 target material:
[0017] 1) TiO2 target material was prepared by solid-state sintering;
[0018] 2) The prepared TiO2 target material was pretreated by using sandpaper with a mesh size of low to high for preliminary polishing and fine polishing to obtain a TiO2 target material with a purity of 99.999 at.%.
[0019] Pulsed laser deposition: The TiO2 target is placed in a vacuum growth chamber and positioned opposite the Al2O3 substrate. The growth parameters are controlled: growth temperature, oxygen pressure, laser energy density, laser frequency, and target-substrate distance. The deposition time is controlled according to the target thickness of the rutile TiO2 ferroelectric thin film layer. After deposition, the temperature is maintained in the vacuum growth chamber to obtain an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity.
[0020] Furthermore, in the pretreatment of the Al2O3 substrate, the Al2O3 substrate is a pure (0001) oriented Al2O3 single crystal substrate; the organic solvents used for ultrasonic cleaning are ethanol and acetone, respectively.
[0021] Vacuum growth chamber pressure <10 -2 Pa, the heating and baking temperature is 500℃-800℃, and the time is 10min-20min.
[0022] Furthermore, in the preparation of TiO2 target material, step 1) uses 99.999 at.% pure rutile TiO2 powder, which is cold isostatically pressed under a pressure of 300 MPa for 15 min. Then, the formed sample is heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, it is cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0023] Furthermore, in the preparation of TiO2 target material, in step 2), the initial sandpaper used for polishing is 600 grit, and the fine sandpaper used for polishing is 800 grit, 1000 grit and 2000 grit respectively, with each type of sandpaper requiring 5 minutes of polishing time.
[0024] Furthermore, in pulsed laser deposition, the growth parameters are: growth temperature 700℃-800℃, oxygen pressure 1×10⁻⁶. - 2 Pa-4×10 -2 Pa, laser energy density 2J / cm 2- 3J / cm 2 The laser frequency is 4Hz-6Hz, and the distance between the target and the substrate is 4cm-6cm.
[0025] Furthermore, in pulsed laser deposition, the deposition time is 10 min to 50 min; the heat preservation time after deposition is 10 min to 15 min.
[0026] Thirdly, this invention discloses the application of an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in the field of photocatalytic water splitting.
[0027] Advantages and effects of the present invention:
[0028] 1. The ultra-dense nanotwinned rutile TiO2 ferroelectric thin film proposed in this invention exhibits room-temperature ferroelectricity, with a remanent polarization of 24.5 μC / cm. 2 The above demonstrates excellent performance.
[0029] 2. The ultra-dense nanotwinned rutile TiO2 ferroelectric thin film proposed in this invention does not require any element doping or the introduction of in-plane or out-of-plane strain. Its ferroelectricity originates from the intrinsic structure of the material, and the mechanism is clear. The preparation process is relatively simple, and it can be prepared by pulsed laser deposition without the need for pre-sputtering of the target surface. The preparation process is simplified, highly reproducible, and conducive to large-scale production and application.
[0030] 3. The ultra-dense nanotwinned rutile TiO2 ferroelectric thin film proposed in this invention improves the photocatalytic hydrogen production efficiency by more than 9.5 times compared with single-crystal rutile TiO2 thin film, which is conducive to promoting the further development of TiO2-based ferroelectric photocatalysts.
[0031] 4. The ultra-dense nanotwinned rutile TiO2 ferroelectric thin film proposed in this invention provides a novel approach to introducing ferroelectricity into non-ferroelectric materials, expands the application range of rutile TiO2, and lays the foundation for high-quality ferroelectric functional materials based on TiO2 and photocatalytic water splitting devices. Attached Figure Description
[0032] Figure 1 The image shows the microstructure of the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 film on an Al2O3 (0001) substrate in Example 1. (a) is a bright-field transmission electron microscope image observed along the planar direction; (b) is a selected area electron diffraction (SED) image of the ultra-dense nanotwinned rutile TiO2 film bulk; (c) is a bright-field transmission electron microscope image observed along the cross-sectional direction; and (d) is a selected area electron diffraction (SED) image of the heterojunction interface between the ultra-dense nanotwinned rutile TiO2 film and the Al2O3 (0001) substrate.
[0033] Figure 2 The atomic and electronic structure diagrams of the ultra-dense nanotwinned rutile TiO2 thin film with room temperature ferroelectricity in Example 1 are shown below. (a) is a low-magnification atomic-level high-angle annular dark-field image taken along the
[100] zone axis; (b) is an atomic layer-resolved electron energy loss spectrum of the twin boundary (TB) and the rutile TiO2 matrix region; (c) is a high-magnification high-angle annular dark-field image characterizing the (011) twin boundary along the
[100] zone axis; and (d) is an annular bright-field image characterizing the (011) twin boundary along the
[100] zone axis.
[0034] Figure 3The image shows the simulation and calculation results of the twin boundaries of the ultra-dense nanotwinned rutile TiO2 thin film (011) with room temperature ferroelectricity in Example 1. Among them, (a) is the simulated image of the high-angle annular dark field image and annular bright field image of the rutile TiO2 (011) twin boundary; (b) is the atomic model diagram of the rutile TiO2 (011) twin boundary; (c) is the displacement of titanium ions from the octahedral center and the calculated value of the ferroelectric polarization intensity of the twin boundary; (d) is the comparison diagram of the local density of states (LDOS) of the bulk phase and the twin boundary.
[0035] Figure 4 The images show the ferroelectric properties of the ultra-dense nanotwinned rutile TiO2 thin film with room-temperature ferroelectricity in Example 1. (a) is the surface morphology obtained by piezoelectric force microscopy after ±20V polarization treatment; (b) is the writing voltage pattern; (c) is the phase diagram obtained by piezoelectric force microscopy after ±20V polarization treatment; (d) is the amplitude diagram obtained by piezoelectric force microscopy after ±20V polarization treatment; (e) is the local test curve of piezoelectric force microscopy (PFM), where the blue dots are amplitude-voltage butterfly curves and the orange dots are phase-voltage hysteresis loops; and (f) is the ferroelectric hysteresis curve measured at room temperature.
[0036] Figure 5 The image shows the photocatalytic performance characterization of the ultra-dense nanotwinned rutile TiO2 film with room temperature ferroelectricity in Example 1. (a) shows the gas yield in the photocatalytic water splitting test; (b) shows the steady-state photoluminescence (PL) spectrum; (c) shows the transient photoluminescence (TRPL) spectrum; (d) shows the surface potential distribution of the control group single-crystal rutile TiO2 under full-spectrum illumination; (e) shows the surface potential (SPV) distribution image of the ultra-dense nanotwinned rutile TiO2 film under full-spectrum illumination; and (f) shows the surface photovoltage (SPV) line scan curve. Detailed Implementation
[0037] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.
[0038] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 20 nm-400 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is ≥27.2 μC / cm. 2 .
[0039] A method for preparing an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity includes the following steps:
[0040] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 Baking in a vacuum growth chamber at 500℃-800℃ for 10-20 minutes.
[0041] Preparation of TiO2 target material:
[0042] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0043] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0044] Pulsed laser deposition: The TiO2 target is placed in a vacuum growth chamber, opposite to the Al2O3 substrate, and the growth parameters are controlled as follows: growth temperature 700℃-800℃, oxygen pressure 1×10⁻⁶. -2 Pa-4×10 -2 Pa, laser energy density 2J / cm 2 ~3J / cm 2 The laser frequency is 4Hz-6Hz and the target-substrate distance is 4cm-6cm. The deposition time is adjusted to 10min-50min according to the target thickness (20nm-400nm) of the rutile TiO2 thin film ferroelectric thin film layer. After deposition, the film is kept at a constant temperature in the vacuum growth chamber for 10min-15min to obtain an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity.
[0045] Application of an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in the field of photocatalytic water splitting.
[0046] This invention describes the growth of ultra-dense nanotwinned rutile TiO2 films with room-temperature ferroelectricity on Al2O3 (0001) single-crystal substrates using a pulsed laser deposition system. The grown rutile TiO2 films exhibit ultra-high density {011} twins, with each twin wafer consisting of only 3-6 atomic layers. This is due to the Ti within the twin boundary structural units... 4+ The ions are significantly deviated from the center of the oxygen sublattice, resulting in ferroelectricity similar to that of a displaced ferroelectric. The presence of numerous twin interfaces enables this ultra-dense nanotwinned rutile TiO2 film to exhibit room-temperature ferroelectricity. This invention utilizes a pulsed laser deposition system to grow ultra-dense nanotwinned rutile TiO2 films with room-temperature ferroelectricity. The process is controllable and facilitates the growth of high-quality films, laying the foundation for the design and fabrication of high-performance ferroelectric materials.
[0047] In terms of material selection, this invention uses rutile TiO2 with low twinning energy, utilizing the Ti within the structural units at its twinning interfaces. 4+ The characteristic of ions significantly deviating from the center of the oxygen sublattice allows for a substantial increase in the density of the twin interfaces, resulting in a significant increase in the ferroelectric component and thus exhibiting macroscopic room-temperature ferroelectricity. Structurally, this invention presents a multi-domain ferroelectric thin film structure, achieving in-plane distribution of ferroelectric polarization through crystal epitaxial growth technology. In terms of fabrication, this invention utilizes a pulsed laser deposition system for single-crystal epitaxial growth, and by precisely controlling various growth parameters during the fabrication process, achieves the preparation of ultra-dense nanotwinned rutile TiO2 thin films exhibiting room-temperature ferroelectricity.
[0048] Example 1
[0049] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 100 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.6 μC / cm. 2 .
[0050] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 1 includes the following steps:
[0051] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 750°C for 15 minutes.
[0052] Preparation of TiO2 target material:
[0053] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0054] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0055] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 750℃, oxygen pressure 2.6 × 10⁻⁶. -2 Pa, laser energy density 3J / cm 2 With a laser frequency of 5Hz and a target-substrate distance of 5cm, a 100nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0056] Microstructure characterization and ferroelectric mechanism analysis:
[0057] The ultra-dense nanotwinned rutile TiO2 thin film material with room-temperature ferroelectricity was tested using transmission electron microscopy, such as... Figure 1 As shown, the rutile TiO2 film exhibits extremely high twin density, with numerous {011} twin interfaces present. The twin lamellae exist within the film in three 120° rotational variants. Figure 2 As shown in (a), the atomic structure of rutile TiO2 {011} nanotwins is visible, facilitating the understanding of the atomic arrangement at the twin boundaries. The thickness of the twin lamellae is only 3-6 atomic layers; Figure 2 (b) shows Ti L 2,3 The Ti ions in both the edge, twin boundary, and matrix are in the +4 valence state; for example Figure 2 As shown in (c) and 2(d), the twin boundaries indicated by the orange arrows are clear and steep. The TiO6 octahedrons (marked with white hexagons) at the {011} twin boundaries are non-centrosymmetric, and the Ti ions are significantly deviated from the center of the octahedrons.
[0058] First-principles calculations were used to systematically study the atomic / electronic structure and ferroelectric polarization microstructure of the {011} twin boundaries in ultradense nanotwinned rutile TiO2 films. Based on high-precision atomic-resolution HAADF and ABF images obtained experimentally, an initial atomic model of the rutile TiO2 (011) twin boundaries was established. Figure 3 As shown in (a) and 3(b), the HAADF / ABF image of the
[100] zone axis direction simulated by this model is in high agreement with the experimental results, which verifies the accuracy of the atomic model and provides an atomic-scale benchmark for subsequent twin boundary ferroelectricity studies. Figure 3 (b) shows that the titanium ions at the rutile TiO2 (011) twin boundaries are significantly deviated from the center of the TiO6 octahedron (white hexagon), indicating ferropolarization at the twin boundaries. Figure 3 As shown in (c), based on the titanium ion displacement and Born effective charge Z Ti* = 5.38 The rutile TiO2 twin boundary edge
[01] was calculated. The ferroelectric polarization intensity in the [] direction is 73.7 μC / cm²; this polarization value drops sharply to zero within two adjacent TiO6 octahedral layers, demonstrating high spatial localization. The local density of states (LDOS) of the twin boundary and bulk regions was compared to analyze the differences in their electronic structures, such as... Figure 3 As shown in (d), the twin boundary band gap (2.0 eV) is slightly larger than that in the bulk region (1.9 eV). This phenomenon originates from the shrinkage of the Ti-O bond length at the twin boundary induced by the polarization effect. The Ti-O bond length at the twin boundary is 1.87 Å, while that in the bulk is 1.96 Å, a reduction of 4.6%. The twin boundary induces Ti ions to deviate from the center of the TiO6 octahedron, forming a local structural distortion, which directly triggers Ti-O bond polarization. At the same time, the shortening of the bond length strengthens the hybridization of Ti 3d and O 2p orbitals, further stabilizing the polarization. This proves that the twin boundary is the key to regulating Ti-O bond polarization and realizing interfacial ferroelectricity.
[0059] Rutile TiO2 itself has a centrosymmetric structure with the centers of positive and negative charges coinciding, and lacks intrinsic ferroelectricity. However, the ultra-dense nanotwinned rutile TiO2 film of this invention breaks this centrosymmetry through ultra-high density {011} nanotwin boundaries with non-coinciding positive and negative charges, generating spontaneous polarization. Within the twin boundary structural units, Ti… 4+ Ions, subjected to asymmetric stresses from the lattices on either side, deviate from the central position of the oxygen octahedron, forming an electric dipole moment along a specific direction, i.e., spontaneous polarization; three 120° rotated twin variants intertwine to form a high-density twin boundary network penetrating the thin film, with a large amount of Ti... 4+ The coordinated arrangement of electric dipole moments generated by displacement enables the thin film to exhibit macroscopic ferroelectricity.
[0060] Performance testing:
[0061] (1) Ferroelectric performance testing:
[0062] Electrodes were fabricated on ultra-dense nanotwinned rutile TiO2 thin film material using photolithography. In-plane Pt interdigitated electrode devices with a thickness of 100 nm and an electrode gap of 2 μm were sputtered. Hysteresis loops were measured at 1 kHz and room temperature (25 °C) using a ferroelectric measuring instrument (Radiant Technologies, USA; Radiant Multiferroic II). Piezoelectric microscopy measurements were performed using a Cypher Asylum Research platform with a conductive Pt-coated silicon cantilever probe. The sample was mounted on the piezoelectric microscope stage via conductive tape. Measurements were performed in contact mode, with the cantilever in contact with the sample surface. A 20 V, 2 kHz AC voltage was applied between the probe tip and the bottom electrode. The out-of-plane piezoelectric response signal was recorded as a function of the applied voltage, and piezoelectric microscope amplitude and phase images were obtained to visualize the ferroelectric domain structure.
[0063] like Figure 4 As shown, the ultra-dense nanotwinned rutile TiO2 ferroelectric thin film exhibits typical ferroelectric hysteresis characteristics, with a remanent ferroelectric polarization as high as 27.6 μC / cm. 2 With a coercivity of 78.4 MV / m, it exhibits excellent ferroelectric properties.
[0064] (2) Photocatalytic water splitting performance test:
[0065] The PL (xenon lamp excitation source) and TRPL (LED pulsed laser source) spectra of the samples were obtained at room temperature using an Edinburgh Instruments FLSP-920 fluorescence spectrophotometer. The spatial distribution of surface photovoltage was measured using a Bruker KPFM (Bruker dimension icon) with a Pt / Ir coated Si tip (1N / m-5N / m, 60kHz-100kHz). Ten 10mm × 10mm ultra-dense nanotwinned rutile TiO2 ferroelectric films were fixed on PTFE supports and transferred to a container containing 100mL of distilled water. A 1.0mL solution of 1mg / mL H2PtCl6 was dispersed into the container. The container was then evacuated and irradiated with a 300W xenon lamp for in-situ photodeposition, loading Pt nanoparticles onto the film surface as a hydrogen evolution co-catalyst. The photocatalytic water splitting was tested using an automated testing system. After evacuation, the sample was irradiated with a xenon lamp with a wavelength ≥300nm to simulate sunlight. The circulating water temperature was maintained at 283K. The gases generated within the system were analyzed at specified time intervals using a gas chromatograph (Agilent Technologies, 6890N).
[0066] Using single-crystal materials as a control group, such as Figure 5 As shown in (a), the ultra-dense nanotwinned rutile TiO2 thin film of this invention exhibits excellent photocatalytic water splitting performance, with a hydrogen production efficiency approximately 10 times that of single-crystal materials. Figure 5 As shown in (b) and 5(c), the fluorescence intensity of the ultra-dense nanotwinned rutile TiO2 film of this invention is significantly improved, with the PL intensity of the film being an order of magnitude higher than that of the single-crystal material. However, its fluorescence lifetime is shortened. This phenomenon originates from the inherent depolarization field effect of ferroelectric materials. The depolarization field inside the film can accelerate carrier migration, suppress nonradiative recombination caused by deep-level defects, shorten carrier capture time, and reduce the fluorescence quenching probability. KPFM characterization further verified the above mechanism, as shown in... Figure 5As shown in 5(d), 5(e), and 5(f), under full-spectrum illumination, the surface photovoltage (SPV) of the ultra-dense nanotwinned rutile TiO2 film of this invention is significantly higher than that of single-crystal R-TiO2. The surface SPV of the ultra-dense nanotwinned rutile TiO2 film is approximately 254 mV, while that of single-crystal rutile TiO2 is approximately 95 mV. The SPV of the nanotwinned ferroelectric film is approximately 2.7 times that of the latter, indicating that its photogenerated carrier separation efficiency is significantly improved compared to single-crystal rutile TiO2. This result is highly consistent with the conclusions of PL and TRPL spectra. Therefore, the ultra-dense nanotwinned rutile TiO2 film of this invention shows great potential in the application of high-quality ferroelectric functional materials and photocatalytic water splitting.
[0067] Example 2
[0068] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 200 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.6 μC / cm. 2 .
[0069] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 2 includes the following steps:
[0070] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 750°C for 15 minutes.
[0071] Preparation of TiO2 target material:
[0072] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0073] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0074] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 750℃, oxygen pressure 2.6 × 10⁻⁶. -2 Pa, laser energy density 3J / cm 2 With a laser frequency of 5Hz and a target-substrate distance of 5cm, a deposition growth was carried out for 50min to obtain an ultra-dense nanotwinned rutile TiO2 film with a thickness of 200nm. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0075] Performance testing:
[0076] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room temperature ferroelectricity in Example 2 were tested using the test method of Example 1. The remanent polarization was approximately 27.6 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0077] Example 3
[0078] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 200 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.2 μC / cm. 2 .
[0079] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 3 includes the following steps:
[0080] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 750°C for 15 minutes.
[0081] Preparation of TiO2 target material:
[0082] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0083] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0084] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 700℃, oxygen pressure 2.6 × 10⁻⁶. -2 Pa, laser energy density 3J / cm 2 With a laser frequency of 5Hz and a target-substrate distance of 5cm, a 100nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0085] Performance testing:
[0086] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room temperature ferroelectricity in Example 3 were tested using the test method of Example 1. The remanent polarization was approximately 27.2 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0087] Example 4
[0088] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 100 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.6 μC / cm. 2 .
[0089] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 4 includes the following steps:
[0090] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 800℃ for 20 minutes.
[0091] Preparation of TiO2 target material:
[0092] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0093] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0094] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 800℃, oxygen pressure 4.0 × 10⁻⁶. -2 Pa, laser energy density 3J / cm 2 With a laser frequency of 5Hz and a target-substrate distance of 5cm, a 100nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 10min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0095] Performance testing:
[0096] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room temperature ferroelectricity in Example 4 were tested using the test method of Example 1. The remanent polarization was approximately 27.6 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0097] Example 5
[0098] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 30 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 24.5 μC / cm. 2 .
[0099] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 5 includes the following steps:
[0100] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 500°C for 10 minutes.
[0101] Preparation of TiO2 target material:
[0102] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0103] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0104] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 700℃, oxygen pressure 1.0 × 10⁻⁶. -2 Pa, laser energy density 2J / cm 2 With a laser frequency of 6 Hz and a target-substrate distance of 6 cm, a 30 nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 10 min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 10 min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0105] Performance testing:
[0106] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room-temperature ferroelectricity in Example 5 were tested using the test method of Example 1. The remanent polarization was approximately 24.5 μC / cm. 2 The hydrogen production rate is approximately 9.5 times that of single-crystal materials.
[0107] Example 6
[0108] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 100 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The polarization of the ultra-dense nanotwinned rutile TiO2 film is divided into three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.7 μC / cm. 2 .
[0109] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 6 includes the following steps:
[0110] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 750°C for 15 minutes.
[0111] Preparation of TiO2 target material:
[0112] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0113] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0114] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 750℃, oxygen pressure 3.0 × 10⁻⁶. -2 Pa, laser energy density 2.5 J / cm² 2 With a laser frequency of 4Hz and a target-substrate distance of 4cm, a 100nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0115] Performance testing:
[0116] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room-temperature ferroelectricity in Example 6 were tested using the test method of Example 1. The remanent polarization was approximately 27.7 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0117] Example 7
[0118] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 100 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with thicknesses ranging from 3 to 6 atomic layers. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.4 μC / cm. 2 .
[0119] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 7 includes the following steps:
[0120] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 700°C for 20 minutes.
[0121] Preparation of TiO2 target material:
[0122] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0123] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0124] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 700℃, oxygen pressure 3.0 × 10⁻⁶. -2 Pa, laser energy density 2.5 J / cm² 2 With a laser frequency of 6 Hz and a target-substrate distance of 6 cm, a 100 nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30 min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15 min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0125] Performance testing:
[0126] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room-temperature ferroelectricity in Example 7 were tested using the test method of Example 1. The remanent polarization was approximately 27.4 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0127] Example 8
[0128] An ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is disclosed. The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition and has a thickness of 100 nm. The ferroelectric rutile TiO2 film exhibits ultra-dense nanotwins with space group P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, and α=β=γ=90°. The nanotwin lamellae exist within the rutile TiO2 film in three 120° rotation variants, with each lamellae being 3-6 atomic layers thick. Excessive {011} twin interfaces are present in the rutile TiO2 film, where Ti is +4 valence. The ultra-dense nanotwinned rutile TiO2 film exhibits polarization along three in-plane directions, with each direction separated by a 120° angle. The remanent polarization intensity is 27.8 μC / cm. 2 .
[0129] The preparation method of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity in Example 8 includes the following steps:
[0130] Pretreatment of Al2O3 substrate: Pure (0001) oriented Al2O3 single crystal substrates were ultrasonically cleaned in ethanol and acetone for 10 min each to remove residual organic matter adhering to the substrate surface. Then, the Al2O3 substrates were transferred to an environment with a pressure <10. -2 The vacuum growth chamber of Pa was baked at 800°C for 15 minutes.
[0131] Preparation of TiO2 target material:
[0132] 1) Preparation of TiO2 target material by solid-state sintering: 99.999 at.% pure rutile TiO2 powder was used and cold isostatically pressed at 300 MPa for 15 min. The sample was then heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, the sample was cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
[0133] 2) The prepared TiO2 target material was pretreated. First, the target surface was initially polished for 5 minutes using 600-grit sandpaper to remove surface imperfections and achieve a uniform and smooth surface. Then, 800-grit, 1000-grit, and 2000-grit sandpaper were used for fine polishing for 5 minutes each to gradually improve the surface smoothness, ultimately obtaining a smooth, delicate, and consistent surface quality. Finally, the target surface was cleaned with acetone and alcohol.
[0134] Pulsed laser deposition: A TiO2 target is placed in a vacuum growth chamber, opposite to an Al2O3 substrate. Growth parameters are controlled as follows: growth temperature 800℃, oxygen pressure 4.0 × 10⁻⁶. -2 Pa, laser energy density 3J / cm 2 With a laser frequency of 4Hz and a target-substrate distance of 5cm, a 100nm thick ultra-dense nanotwinned rutile TiO2 film was obtained by deposition and growth for 30min. After deposition, the film was kept at a constant temperature in a vacuum growth chamber for 15min to obtain an ultra-dense nanotwinned rutile TiO2 film material with room temperature ferroelectricity.
[0135] Performance testing:
[0136] The ferroelectric properties and photocatalytic water splitting performance of the ultra-dense nanotwinned rutile TiO2 thin film with room temperature ferroelectricity in Example 8 were tested using the test method of Example 1. The remanent polarization was approximately 27.8 μC / cm. 2 The hydrogen production rate is about 10 times that of single-crystal materials.
[0137] In summary, this invention achieves the preparation of high-quality ultra-dense nanotwinned rutile TiO2 ferroelectric thin films via pulsed laser deposition. These films exhibit excellent ferroelectric properties and photocatalytic water splitting performance, particularly notable for their lack of dopant element introduction and stress-strain modulation, as well as their high remanent polarization. This invention utilizes transmission electron microscopy to investigate the microstructure and mechanism of the ultra-dense nanotwinned rutile TiO2 thin films, elucidating the intrinsic mechanism of their ferroelectric properties. The ferroelectric properties and photocatalytic water splitting performance of the nanotwinned rutile TiO2 thin films were systematically measured using piezoelectric microscopy, a ferroelectric testing instrument, and a photocatalytic measurement system. Ferroelectric property measurements revealed that the nanotwinned rutile TiO2 thin films exhibit room-temperature ferroelectricity, with polarization distributed along three in-plane directions, each with an angle of 120° between them, and a remanent polarization intensity reaching 27.6 μC / cm². 2 Photocatalytic water splitting performance measurements revealed that the photoluminescence intensity of the nanotwinned rutile TiO2 film was significantly enhanced, exceeding that of single-crystal rutile TiO2 by an order of magnitude, although its fluorescence lifetime was shortened. However, its photocatalytic hydrogen production efficiency was 10 times that of single-crystal rutile TiO2. This invention opens up a novel approach to induced ferroelectricity through grain boundaries, laying the foundation for further exploration and research of novel ferroelectric materials and TiO2-based ferroelectric photocatalytic water splitting devices.
Claims
1. A room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material, characterized in that, The material comprises an Al2O3 substrate and a rutile TiO2 ferroelectric thin film layer grown on the Al2O3 substrate. The rutile TiO2 ferroelectric thin film layer is epitaxially grown on the Al2O3 substrate by pulsed laser deposition. The rutile TiO2 ferroelectric thin film layer contains ultra-dense nanotwins with a space group of P4 / mnm, lattice constants a=b=4.594Å, c=2.959Å, α=β=γ=90°. The polarization of the ultra-dense nanotwin rutile TiO2 thin film is divided into three directions along the plane, with an angle of 120° between each direction.
2. The ultra-dense nanotwinned rutile TiO2 thin film material with room-temperature ferroelectricity as described in claim 1, characterized in that, The thickness of the rutile TiO2 ferroelectric thin film layer is 20nm-400nm; Nanotwinned crystalline layers exist within the rutile TiO2 film in three 120° rotation variants. The thickness of the crystalline crystalline layers is 3-6 atomic layers. There is an excess of {011} twin interfaces in the rutile TiO2 film, and Ti at the twin interfaces is +4 valence.
3. The ultra-dense nanotwinned rutile TiO2 thin film material with room-temperature ferroelectricity as described in claim 1, characterized in that, The remanent polarization of the ultradense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity is ≥27.2 μC / cm. 2 .
4. A method for preparing an ultra-dense nanotwinned rutile TiO2 thin film material with room-temperature ferroelectricity as described in claim 1, characterized in that, Includes the following steps: Pretreatment of Al2O3 substrate: The Al2O3 substrate is ultrasonically cleaned in an organic solvent, and then transferred to a vacuum growth chamber for heating and baking. Preparation of TiO2 target material: 1) TiO2 target material was prepared by solid-state sintering; 2) The prepared TiO2 target material was pretreated by using sandpaper with a mesh size of low to high for preliminary polishing and fine polishing to obtain a TiO2 target material with a purity of 99.999 at.%. Pulsed laser deposition: The TiO2 target is placed in a vacuum growth chamber and positioned opposite the Al2O3 substrate. The growth parameters are controlled: growth temperature, oxygen pressure, laser energy density, laser frequency, and target-substrate distance. The deposition time is controlled according to the target thickness of the rutile TiO2 ferroelectric thin film layer. After deposition, the temperature is maintained in the vacuum growth chamber to obtain an ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity.
5. The method for preparing the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material as described in claim 4, characterized in that, In the pretreatment of the Al2O3 substrate, the Al2O3 substrate is a pure (0001) oriented Al2O3 single crystal substrate; the organic solvents used for ultrasonic cleaning are ethanol and acetone, respectively. Vacuum growth chamber pressure <10 -2 Pa, the heating and baking temperature is 500℃-800℃, and the time is 10min-20min.
6. The method for preparing the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material as described in claim 4, characterized in that, In the preparation of TiO2 target material, step 1) uses 99.999 at.% pure rutile TiO2 powder, which is cold isostatically pressed under a pressure of 300 MPa for 15 min. Then the shaped sample is heated to 1000℃ at a rate of 5℃ / min, then heated to 1500℃ at a rate of 3℃ / min and held for 10 h. Finally, it is cooled to 500℃ at a rate of 3℃ / min and then cooled in the furnace.
7. The method for preparing the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material as described in claim 4, characterized in that, In the preparation of TiO2 target material, step 2) uses 600-grit sandpaper for initial polishing, and 800-grit, 1000-grit, and 2000-grit sandpaper for fine polishing, with each type of sandpaper requiring 5 minutes of polishing time.
8. The method for preparing the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material as described in claim 4, characterized in that, In pulsed laser deposition, the growth parameters are: growth temperature 700℃-800℃, oxygen pressure 1×10⁻⁶. -2 Pa-4×10 -2 Pa, laser energy density 2J / cm 2- 3J / cm 2 The laser frequency is 4Hz-6Hz, and the distance between the target and the substrate is 4cm-6cm.
9. The method for preparing the room-temperature ferroelectric ultra-dense nanotwinned rutile TiO2 thin film material as described in claim 4, characterized in that, In pulsed laser deposition, the deposition time is 10 min to 50 min; the holding time after deposition is 10 min to 15 min.
10. The application of the ultra-dense nanotwinned rutile TiO2 thin film material with room temperature ferroelectricity as described in claim 1 in the field of photocatalytic water splitting.