Nanostructured lithium niobate synthesis process at low temperature

Description

PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE Technological sector of invention

[01] In general, the present invention belongs to the technological sector of nanomaterial synthesis, in the areas of Materials Engineering, Biophysics and Biotechnology, and refers, more specifically, to a low-temperature synthesis process of nanostructured lithium niobate to obtain new materials to act as cathodes in solid-state batteries based on lithium niobate nanoceramics. To this end, it reveals a possibility for the development of lithium niobate nanoparticles through Sol-Gel synthesis in a single step, using low-cost and highly available reagents, such as lithium carbonate and niobium ammonium oxalate or niobium pentoxide, to obtain lithium niobate nanoparticles, these reagents being abundantly available in the Brazilian market, whose reserves (lithium and niobium) are among the largest in the world.

[02] Through a synthesis process that uses simple and readily available instruments, such as a beaker and magnetic stirrer during the synthesis process, and by using a crystallization temperature between 250-600 °C (optimum temperature of 450 °C) for 2 h in a muffle furnace to obtain lithium niobate, it is revealed that such characteristics have not yet been reported in the literature for obtaining lithium niobate nanoparticles, resulting in nanometric material, with a particle size between 40 and 75 nm and a specific surface area of ​​27-96 m2 / g. Known state of the art

[03] Lithium niobate (LiNbOa) is widely used in the telecommunications market, for example in mobile phones and optical modulators; as optical polarizing components due to its wide transparency range and low cost; as a material for surface acoustic wave devices; for laser frequency doubling, nonlinear optics, Pockels cells; optical parametric oscillators, Q-switching devices for lasers, optical switches for Petition 870250007443, dated 01 / 29 / 2025, page 10 / 27 2 / 12 GHz frequencies; for inducing cell death in tumor cell cultures when doped with iron and excited with visible light.

[04] Niobates (ANbO3, A = Na, K, Ag, Cu, Li) have attracted considerable attention from the scientific community due to their varied nonlinear optical properties, ferroelectricity, piezoelectricity, pyroelectricity and photocatalytic properties. Lithium niobate (LiNbO3) is part of the group of ferroelectric materials (Kong et al., 2020).

[05] Lithium niobate is a compound of global relevance, especially to Brazil, which has the world's largest active niobium reserve (about 90% of world production). Niobium has been essential as an alloying material to enhance properties in various industrial sectors, such as the oil, automotive and shipbuilding industries, providing greater thermal and electrical conductivity, as well as improving the malleability, ductility and corrosion resistance of materials (CBMM, 2024).

[06] In the synthesis of LiNbO3, Nb2O5 is commonly used as a precursor because it is more accessible and economical, significantly reducing the costs of large-scale production (Liu et al., 2006). This crystalline compound has a perovskite-type structure, being a colorless or yellowish crystal, with a melting point around 1253 °C and a density of 4.64 g / cm3 (Carruthers et al., 1971; Xu, 2013). Its structural phase transition occurs in the temperature range between 1150 and 1210 °C, known as the Curie temperature, where it changes from a paraelectric to a ferroelectric phase (Mastelaro, 2007). However, niobium ammonium oxalate is more reactive and efficient.

[07] The properties of LiNbO3 are based on its crystalline structure and composition, which makes it a semiconductor with high coefficients in properties such as electro-optical, pyroelectric, nonlinear optical and piezoelectric (Guarino et al., 2007; Syuy et al., 2018). Its physical and optical characteristics are widely explored in different fields, from the production of high-voltage sensors to photonic devices such as lasers, photorefractors and Petition 870250007443, dated 01 / 29 / 2025, page 11 / 27 3 / 12 electro-optics and even batteries (Fan et al., 2014; Oesterling et al., 2015, Courjal et al., 2009; Zhang et al., 2020).

[08] Furthermore, it demonstrates promising photocatalytic properties under UV radiation, indicating potential as a photocatalyst, since it maintains ferroelectricity to efficiently separate charge carriers for the internal electric field (Huang, 2010; Nechache et al., 2015). They are capable of absorbing a large number of photons, being characterized as good photocatalysts in hydrogen generation (Saito et al., 2011).

[09] Several synthesis methods have been employed to obtain LiNbO3 in an efficient and controlled manner, including sol-gel, solid-state reaction, polymeric precursors, solvothermal, hydrothermal and microwave-assisted hydrothermal (Pitcher et al., 2005; Su et al., 2010; Souza et al., 2002; Chien et al., 2006; Deon et al., 2021).

[010] Advances in the understanding and production of LiNbO3 open doors to increasingly diverse and innovative applications, consolidating its position as a leading material in science and industry.

[011] Table 1 summarizes the information from the LiNbOs synthesis studies mentioned. Table 1. Publications on the synthesis of LiNbO3. Author | Synthesis Method | Method Details | Temperature (°C) | Crystallite Size (nm) | Niederberger et al. (2004) | Solid State Reaction | Crystallization at 220 °C for 4 days | 220 | 20-50 | Sol-Gel at 500 and 600 °C; | Liu et al. | Sol-Gel 240-600 (2008) Hydrothermal Hydrothermal at 240 °C Lisinski and Ratke (2010) Reaction by Sol-Gel Synthesis at 700, 900, 1100 and 1150 °C for 48 h 700-1150 250 ±65 to 1760 ± 800 Cena, Torsoni and Freitas (2016) Pechini Synthesis at 700 °C for 1 h 700 35 Deon et al. (2021) Microwave-Assisted Hydrothermal Synthesis at 260 °C for 2 and 3 h 260 42 and 65 Petition 870250007443, dated 01 / 29 / 2025, page 12 / 27 4 / 12

[012] Prior art shows complex synthesis methodologies, with high cost, multiple processing steps and long synthesis times, in addition to presenting impurities and the presence of a second phase in the development of lithium niobate nanoparticles. The formation of the crystalline phase LiNb3O8, which is undesirable, commonly occurs.

[013] The available methods present several important problems and limitations. The Solid State Reaction method employs long heat treatment times (on the order of many hours and even days). The Pechini method employs higher temperatures (>700°C) and requires excess lithium to avoid secondary phases. The Microwave Assisted Hydrothermal method is technologically complex and expensive.

[014] Other methodologies often use high temperatures, complex equipment and multiple processing steps, and commonly contain impurities, making the processing of lithium niobate nanoparticles more expensive and extremely time-consuming.

[015] Thus, given all the drawbacks of the systems and equipment currently used, described above in the state of the art, a gap is evident in the creation of a low-temperature synthesis process for nanostructured lithium niobate to obtain new materials to act as cathodes in solid-state batteries based on lithium niobate nanoceramics. To this end, a possibility is revealed for the development of lithium niobate nanoparticles through a single-step Sol-Gel synthesis, using low-cost and highly available reagents such as lithium carbonate and niobium ammonium oxalate or niobium pentoxide, to obtain lithium niobate nanoparticles. These reagents are abundantly available in the Brazilian market, whose reserves (lithium and niobium) are among the largest in the world. Petition 870250007443, dated 01 / 29 / 2025, page 13 / 27 5 / 12 New features and objectives of the invention

[016] The synthesis process of nanostructured lithium niobate at low temperature to obtain new materials to act as cathodes for solid-state batteries based on lithium niobate nanoceramics.

[017] For this purpose, a possibility is revealed for the development of lithium niobate nanoparticles through single-step Sol-Gel synthesis, using low-cost and highly available reagents, such as lithium carbonate and niobium ammonium oxalate or niobium pentoxide, to obtain lithium niobate nanoparticles, these reagents being abundantly available in the Brazilian market, whose reserves (lithium and niobium) are among the largest in the world.

[018] The developed nanostructured lithium niobate has potential applications in various engineering fields, including: telecommunications, for example in cell phones and optical modulators; optical polarization components due to their wide transparency range and low cost; material for surface acoustic wave devices; laser frequency doubling, nonlinear optics, Pockels cells; optical parametric oscillators, Q-switching devices for lasers, optical switches for GHz frequencies; production of cell death in tumor cell cultures when doped with iron and excited with visible light.

[019] The raw materials used were: Niobium Pentoxide (Nb2O5, CBMM), Lithium Carbonate (Li2CO3, CBL) and Niobium Ammonium Oxalate (NH4H2NbO(C2O4).3H2O, CBMM). The raw materials were characterized in terms of their chemical, structural, morphological and thermal characteristics, according to the procedures described below.

[020] With the aim of addressing the shortcomings of the current state of the art highlighted above, the present invention patent aims to propose an innovative low-temperature synthesis process for nanostructured lithium niobate to obtain new materials to act as cathodes for solid-state batteries based on lithium niobate nanoceramics. Petition 870250007443, dated 01 / 29 / 2025, page 14 / 27 6 / 12 Description of the attached drawings

[021] In order that the present invention may be fully understood and put into practice by any technician in this technological sector, it will be described in a clear, concise and sufficient manner, based on the attached drawings, which illustrate and support it, listed below:

[022] Figure 1 represents the flowchart of the Lithium Niobate production process described herein.

[023] Figure 2 represents the X-ray diffractograms of samples (a) of niobium oxide and (b) of lithium carbonate.

[024] Figure 3 represents the thermograms (ATG / ATD) of the synthesized materials.

[025] Figure 4 represents the diffractograms (XRD) of the synthesized materials. Detailed description of the invention

[026] The raw materials used were: Niobium Pentoxide (Nb2O5, CBMM), Lithium Carbonate (Li2CO3, CBL) and Niobium Ammonium Oxalate (NH4H2NbO(C2O4).3H2O, CBMM).

[027] The raw materials were characterized in terms of their chemical, structural, morphological and thermal characteristics, in accordance with the procedures indicated in the following items. Characterization of raw materials a) Chemical Analysis

[028] The chemical analysis of the raw materials used was carried out using the X-ray fluorescence technique (Rigaku / ZSX Primus II). b) Structural Analysis

[029] The structural analysis by X-ray diffraction aims to identify the crystalline phases present in the raw materials used, which were determined on a Shimadzu X-ray diffractometer, model LABX XRD-6000, with 30 kV and a current of 30 mA. Petition 870250007443, dated 01 / 29 / 2025, page 15 / 27 7 / 12

[030] A copper tube (CuKa radiation) with a 2θ scan range of 5 to 85° was used. The diffractograms obtained were compared with standards available in the Joint Committee on Powder Diffraction-International Centre for Diffraction Data (JCPDS) database. The average crystallite size was calculated using the Scherrer equation (Equation 1): _ K λD -baa (Eq.1) where D is the crystallite size (nm), K is the Scherrer constant, which varies from 0.82 to 1.03, according to the form factor (0.91 was used), λ is the wavelength of the X-rays, B is the full width at half height (FWHM) of the XRD peak and θ is the XRD peak position. The full width at half height (FWHM) was obtained using the winfit® software. Sol-Gel Synthesis of Lithium Niobate

[031] Sol-Gel synthesis is a versatile and efficient approach for the production of ceramic materials, providing precise control over the composition and structure of the final product.

[032] Sol-Gel synthesis was used to prepare lithium niobate (LiNbO3), a promising material for application as a cathode in lithium-ion batteries. Figure 1 illustrates the flowchart of the process for obtaining lithium niobate. a) Preparation of precursors.

[033] To obtain the lithium and niobium precursors, Li2CO3 and Niobium Ammonium Oxalate (Synthesis 1) or Li2CO3 and Nb2O5 (Synthesis 2) were used. Both precursors were dissolved in water; citric acid was added as a complexing agent to ensure adequate homogenization. The Li2CO3 and Nb2O5 solutions were kept under stirring at 90 °C for 24 h, resulting in the lithium and niobium precursors. Petition 870250007443, dated 01 / 29 / 2025, page 16 / 27 8 / 12 b) Homogenization and addition of polyethylene glycol

[034] The lithium and niobium solutions, obtained from Syntheses 1 and 2, were then carefully homogenized and polyethylene glycol was added as a gel-forming agent. The presence of this complexing agent helped in the formation of a cohesive matrix during the gelation step. c) Gelation and drying

[035] The homogenized solution was kept under constant agitation until the Sol transformed into a three-dimensional Gel. Subsequently, the Gel was subjected to drying in an oven at 100 °C for 48 h, resulting in the Xerogel. d) Heat treatment

[036] The xerogel was subjected to heat treatment at different temperatures, previously determined by thermal analysis. The temperature variation aimed to find the ideal condition for the formation of lithium niobate. This heat treatment provided crystallization and consolidation of the material's structure. Characterization of the Gels and Lithium Niobate Samples Obtained.

[037] Thermal decomposition behavior was examined by differential thermal analysis (DTA) and thermogravimetric analysis (TGA) simultaneously on a Netzsch STA 449 F3 Jupiter simultaneous thermal analyzer, in synthetic air, at a heating rate of 10°C / min up to 1000°C, using an alumina crucible.

[038] The synthesized samples were analyzed using an X-ray diffractometer (XRD, D-5000 Bruker AXS) with a curved graphite monochromator in secondary beam operating at 40 kV / 25 mA (Cu radiation Ka = 1.54178 Å) and a 2Θ angular range of 10-70° with a step of 0.02° / 2 s. The XRD patterns were compared with the inorganic crystal structure database (ICSD). Petition 870250007443, dated 01 / 29 / 2025, page 17 / 27 9 / 12 using X'Pert HighScorePlus® software to identify the crystalline phases.

[039] The crystallite size and lattice parameters were determined after refinement of the structures, using the Rietveld method (Mccusker et al., 1999; Rietveld, 2014; Sakata; Cooper, 1979). The lattice parameters, occupancy, degree 3 polynomial background, peak scale, and form factors were refined. The goodness of fit (GoF) was used to describe the quality of the refinement. For the calculation of the lower limit of the crystallite size, the Scherrer equation was used from the perspective of the reflection broadening of the crystalline phases present (Langford; Wilson, 1978), as shown in Equation 1.

[040] Specific surface area was determined by BET (Brunauer-EmmetTeller) and BJH (Barrett-Joyner-Halenda) using Quantachrome equipment, model NOVA 1200e. Confirmation / Verification of the Solution

[041] Chemical analysis of niobium oxide (Table 2) shows the presence of major components such as niobium and oxygen. Table 2. Chemical analysis (%m) of niobium oxide and niobium ammonium oxalate. Element Niobium oxide Niobium ammonium oxalate O 40.8 38.1 Al 1.3 0.02 Si 0.03 0.04 Nb 57.7 0.0 Ta 0.13 0.0 C 0.0 6.8 Ni 0.0 55.0

[042] A residual amount of aluminum is also observed, as well as silicon and tantalum, totaling a purity of 93.1% niobium oxide. The niobium ammonium oxalate has 99.96% purity, while the lithium carbonate is pure. Petition 870250007443, dated 01 / 29 / 2025, page 18 / 27 10 / 12

[043] Structural analysis (XRD, Figure 2) shows that despite the presence of residual elements, only the niobium pentoxide (Nb2O5) and lithium carbonate (Li2CO3) phases are evident in Figures 2(a) and 2(b), respectively.

[044] Figure 3 shows the result of thermal analysis performed on the obtained materials, from which exothermic reactions were identified approximately between 220 and 700 °C. To identify the crystalline phases formed, temperatures of 250, 450 and 600 °C were chosen for 2 h. The analysis of the synthesized materials at different temperatures (250, 450 and 600 °C), as determined by the thermal analysis (Figure 3), was conducted by X-ray diffraction (Figure 4) to evaluate the crystallinity and the formation of the desired phase, LiNbO3.

[045] X-ray diffraction revealed that the sample treated at 250 °C still shows the presence of unreacted Nb2Os, indicating an incomplete reaction at that temperature. The incomplete conversion of niobium to the desired LiNbO3 phase suggests the need for a higher temperature to promote complete transformation.

[046] The results obtained at 450 °C indicate the effective formation of the phase of interest, LiNbO3. X-ray diffraction reveals sharp diffraction patterns, characteristic of the crystallinity of the desired phase. This result corroborates the effectiveness of the Sol-Gel synthesis and the influence of temperature on the formation of the phases of interest. For this sample, a broadening in the X-ray reflections is observed, evidencing the presence of small crystallites. This phenomenon can be attributed to the limited crystal growth during the Sol-Gel synthesis, resulting in small particles. This characteristic is crucial for improving the reactivity and efficiency of the material in battery electrode applications.

[047] When the temperature was increased to 600 °C, a continued improvement in the crystallinity of LiNbO3 was observed. X-ray diffraction indicates greater intensity and sharpness in the reflections, suggesting an increase in the structural order of the material. This result may indicate a more extensive crystal growth process, contributing to the enhanced properties of lithium niobate. Petition 870250007443, dated 01 / 29 / 2025, page 19 / 27 11 / 12

[048] Detailed analysis of crystallite size, using the Scherrer equation, provided significant insight into the microstructural evolution of samples synthesized at different temperatures (450 and 600 °C), Table 3. Table 3. Crystalline phases formed, average crystallite size, and specific surface area of ​​the synthesized material. Heat Treatment (°C) Crystalline Phases Crystallite Size (nm) Specific Surface Area (m² / g) 250 LiNbO₃ + Nb₂O₅ -27.1 450 LiNbO₃ 41.28 96.7 600 LiNbO₃ 75.32 36.4

[049] Since the desired crystalline phase did not form in the sample treated at 250 °C, the crystallite size was not calculated. For the sample treated at 450 °C, the analysis indicated an average crystallite size of approximately 41 nm. This value is in accordance with X-ray diffraction patterns, which suggest the effective formation of the desired phase, LiNbO3, with crystallites of reduced dimensions. The choice of the heat treatment temperature of 450 °C favored the obtaining of finer crystallites, resulting in a more reactive structure, as evidenced by the specific surface area of ​​96.7 m2 / g.

[050] When the temperature was raised to 600 °C, a significant increase in the average crystallite size was observed, reaching approximately 75 nm. This increase is consistent with the more extensive crystal growth phenomenon observed in the X-ray diffraction patterns, indicating a more advanced structural maturation of LiNbO3. Scherrer's method provided a quantitative estimate of this increase, highlighting the direct influence of temperature on the crystal growth process.

[051] The results of the specific surface area analysis, measured by BET, corroborate these observations. The sample treated at 450 °C showed a significantly larger specific surface area (96.7 m² / g) compared to the sample treated at 600 °C (36.4 m² / g). This result suggests that the temperature Petition 870250007443, dated 01 / 29 / 2025, page 20 / 27 A lower 12 / 12 density favors the formation of a more porous and reactive structure, contributing to a larger specific surface area.

[052] Based on the results of the crystallite size and specific surface area analysis, the sample chosen for this study was that synthesized by Sol-Gel synthesis and thermally treated at 450 °C / 2 h by Synthesis 1, with Niobium Ammonium Oxalate. This material exhibited an average crystallite size of 41 nm, indicative of a finely crystallized structure, and a specific surface area of ​​96 m² / g, suggesting a highly reactive porous matrix. These characteristics make the sample treated at 450 °C for 2 h an ideal choice, highlighting its potential for applications as a cathode in lithium-ion batteries. This study reinforces the importance of controlled Sol-Gel synthesis to optimize microstructural properties, paving the way for significant advances in energy storage technologies.

[053] Cena, Torsoni and Freitas (2016) synthesized LiNbOa films using Niobium Ammonium Oxalate by the Pechini Method at 700oC / 1 h and obtained a crystallite size of 35 nm, but with 70% excess Li2O by mass.

Claims

1 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE characterized by being composed of the following steps: A) Characterization of raw materials; B) Sol-Gel synthesis of Lithium Niobate; C) Characterization of the gels and samples obtained; D) Confirmation. 2 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claim 1, and further characterized by the raw materials employed being Niobium Pentoxide (Nb2O5, CBMM), Lithium Carbonate (U2CO3, CBL) and Niobium Ammonium Oxalate (NH4H2NbO(C2O4).3H2O, CBMM). 3 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claims 1 and 2, characterized by the raw materials being characterized in terms of their chemical, structural, morphological and thermal characteristics. 4 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claim 1, and further characterized by step A having chemical analysis by means of X-ray fluorescence (Rigaku / ZSX Primus II); and structural analysis by X-ray diffraction with 30 kV and current of 30 mA using a copper tube (CuKa radiation) with a scanning range of 5 to 85°, the average size of the crystalline structure being calculated by the formula D = cos λ, with K varying from 0.82 to 1.

03. 5 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claim 1, and further characterized by step B having the preparation of precursors using Li2CO3 and Niobium Ammonium Oxalate (Synthesis 1) or Li2CO3 and Nb2O5 (Synthesis 2) dissolved in water, with citric acid added as a complexing agent, the Li2O3 and Nb2O5 solutions being kept under agitation at 90 °C for 24 h; homogenization and addition of Polyethylene Glycol as a gel-forming agent resulting in the formation of the cohesive matrix; Gelation and drying under constant agitation until the sol transforms into a three-dimensional gel, which is then subjected to drying in an oven at 100 °C for 48 h, resulting in xerogel; heat treatment for consolidation and crystallization. 6 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claim 1, and further characterized by step C having differential thermal analysis (DTA) and thermogravimetric analysis (TGA), simultaneously, in synthetic air, at a heating rate of 10 °C / min up to 1000 °C in an alumina crucible; analysis in an X-ray diffractometer with a curved graphite monochromator in a secondary beam operating at 40 kV / 25 mA and a 2Θ angular range of 10-70° with a step of 0.02° / 2 s; the crystallite size and lattice parameters being determined after refinement of the structures through the Rietveld method; the specific surface area being determined by BET (Brunauer-Emmet-Teller) and BJH (Barrett-Joyner-Halenda). 7 - PROCESS FOR THE SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claim 1, and further characterized in that step D is preferably carried out by confirming the synthesis of a thermally treated Sol-Gel at 450 °C / 2 h with Niobium Ammonium Oxalate with an average crystallite size with a particle size between 40 and 75 nm and a specific surface area of ​​27-96 m2 / g of reactive porous matrix, treated at 450 °C for 2 h. 8 - PROCESS FOR SYNTHESIS OF NANOSTRUCTURED LITHIUM NIOBATE AT LOW TEMPERATURE, according to claims 1 and 7, and further characterized by having a preferred average crystallite size of 41 nm and a specific surface area of ​​96 m2 / g.

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