High-strain lead-free bismuth-based piezoelectric single crystal and method for preparing the same

Abstract

This invention discloses a high-strain lead-free bismuth-based piezoelectric single crystal and its preparation method, belonging to the technical field of piezoelectric single crystal materials. The main phase of this piezoelectric single crystal is a quaternary solid solution of 0.38Bi(Fe₁ / ₂Nb₁ / ₂)O₃ - 0.22Bi(Mg₁ / ₂Ta₁ / ₂)O₃ - 0.15Bi(Zr₁ / ₂Ti₁ / ₂)O₃ - 0.25BiTiO₃, with the addition of Ho₂O₃, Er₂O₃, ZnO, and Li₂CO₃ dopants, and is prepared using a crucible lowering method. This invention provides a piezoelectric single crystal with an electric field-induced scaling factor of ≥1.5%, a piezoelectric constant d₃₃ of 1800-2200 pC / N, a Curie temperature of 180-200℃, and is lead-free, environmentally friendly, and has stable performance. It completely avoids the existing patent barriers of lead-based and conventional lead-free piezoelectric single crystals, with no infringement risks. The process is controllable and can be mass-produced, making it suitable for high-end fields such as precision drives and microelectromechanical systems.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric single crystal material technology, specifically relating to a lead-free bismuth-based piezoelectric single crystal with an electric field-induced stretching rate ≥1.5% and its preparation method, and particularly to a high-strain piezoelectric single crystal material that circumvents existing patent barriers and is suitable for high-precision driving and microelectromechanical systems. Background Technology

[0002] Piezoelectric single crystals are core functional materials for realizing the interconversion of electric field and mechanical energy, and are widely used in precision drives, ultrasonic devices, and intelligent sensing. Currently, most piezoelectric single crystals that achieve large strain are lead-based relaxor ferroelectric single crystals, such as PMN-PT and PIN-PMN-PT systems, whose electric field-induced strain can reach more than 1%. However, these materials have a high lead content, which does not meet environmental protection requirements, and the relevant core patents are monopolized by foreign institutions, resulting in a very high risk of patent infringement.

[0003] Existing lead-free piezoelectric single crystal materials, such as barium titanate-based and potassium sodium niobate-based single crystals, generally suffer from defects such as low electric field-induced stretching (usually below 1%), low Curie temperature, and poor stability, making it difficult to meet the high strain requirements of 1.5% for high-end devices. Conventional bismuth-based lead-free single crystals mostly use simple binary or ternary components with a single doping system, which not only have insufficient strain performance but also mostly fall within the scope of existing patent protection, making it impossible to achieve independent intellectual property rights layout.

[0004] To address the aforementioned problems, this invention provides a novel quaternary bismuth-based piezoelectric single crystal system. Through specific component blending and rare-earth doping, it achieves an electric field-induced stretching rate of ≥1.5%, while completely circumventing the patent protection scope of existing lead-based and conventional lead-free piezoelectric single crystals, thus solving the dual technical challenges of existing material performance and patent infringement. Summary of the Invention

[0005] This invention discloses a high-strain lead-free bismuth-based piezoelectric single crystal and its preparation method, belonging to the technical field of piezoelectric single crystal materials. The main phase of this piezoelectric single crystal is a quaternary solid solution of 0.38Bi(Fe1 / 2Nb1 / 2)O3 - 0.22Bi(Mg1 / 2Ta1 / 2)O3 - 0.15Bi(Zr1 / 2Ti1 / 2)O3 - 0.25BiTiO3, with the addition of Ho2O3, Er2O3, ZnO, and Li2CO3 dopants. It is prepared using a crucible lowering method. The electric field-induced stretching of the piezoelectric single crystal of this invention is ≥1.5%, and the piezoelectric constant dp is [not specified in the original text]. 33With a yield of 1800-2200 pC / N and a Curie temperature of 180-200℃, this lead-free, environmentally friendly, and stable piezoelectric single crystal completely avoids the patent barriers of existing lead-based and conventional lead-free piezoelectric single crystals, eliminating the risk of infringement. The process is controllable and mass-producible, making it suitable for high-end fields such as precision drives and microelectromechanical systems. This invention addresses the problems of poor environmental performance and high patent barriers of existing lead-based piezoelectric single crystals, and insufficient strain performance and high infringement risks of conventional lead-free piezoelectric single crystals. It provides a lead-free bismuth-based piezoelectric single crystal with an electric field-induced stretching rate ≥1.5%, along with its preparation method. This single crystal is lead-free, environmentally friendly, and has stable performance, and does not fall within the scope of any existing piezoelectric single crystal patent protection, possessing independent intellectual property rights. Technical solution

[0006] 1. Piezoelectric single crystal formulation This invention relates to a high-strain lead-free bismuth-based piezoelectric single crystal, with a main phase being a quaternary bismuth-based perovskite solid solution, and a molar ratio composition of: 0.38Bi(Fe1 / 2Nb1 / 2)O3 - 0.22Bi(Mg1 / 2Ta1 / 2)O3 - 0.15Bi(Zr1 / 2Ti1 / 2)O3 -0.25BiTiO3; Based on the aforementioned host phase, a composite dopant is added, with the dopant mole fraction relative to the host phase being: Ho2O3: 0.4%, Er2O3: 0.3%, ZnO: 0.2%, Li2CO3: 0.1%. 2. Preparation method The piezoelectric single crystal of this invention is prepared by the crucible lowering method, and the specific steps are as follows: (1) Raw material weighing: Select Bi2O3, Fe2O3, Nb2O5, MgO, Ta2O5, ZrO2, TiO2, Ho2O3, Er2O3, ZnO, and Li2CO3 with a purity ≥99.995% as raw materials and weigh them accurately according to the above formula molar ratio; (2) Wet ball milling: The weighed raw material is placed into a nylon ball milling jar, anhydrous ethanol is added as the ball milling medium, zirconia balls are used as grinding balls, the ball-to-material ratio is 5:1, and wet ball milling is performed for 24-30 hours to obtain a uniformly mixed slurry. (3) Drying and sieving: The slurry was vacuum dried at 80°C for 12 hours, ground, and then sieved through a 200-mesh sieve to obtain a mixed powder; (4) Pre-calcination synthesis: The mixed powder was placed in an alumina crucible and pre-calcined at 800°C for 4 hours in an air atmosphere to synthesize a quaternary bismuth-based perovskite phase precursor. (5) Crystal growth: After compacting the precursor powder, it is placed into a platinum crucible and crystal growth is carried out by crucible descent method. The growth temperature is 1320-1360℃, the descent rate is 0.3-0.6mm / h, and the growth atmosphere is Ar+5%O2 mixed atmosphere to suppress bismuth volatilization. (6) Polarization treatment: After the grown single crystal is cut and polished, it is polarized for 30 min under an electric field of 120℃ and 6kV / cm to obtain a high strain lead-free bismuth-based piezoelectric single crystal. Beneficial effects 1. Excellent performance: The electric field-induced stretching rate of the piezoelectric single crystal of this invention can reach 1.5%-1.7%, and the piezoelectric constant d 33 With a strength of 1800-2200 pC / N and a Curie temperature of 180-200℃, it meets the requirements for high strain and high stability applications. 2. Patent security: It adopts a brand-new quaternary bismuth-based lead-free system, abandons lead-based components, avoids the core components of mainstream patents such as PMN-PT and PIN-PMN-PT, and the doping combination is an original Ho-Er-Zn-Li composite system. There are no existing patent reports, completely avoiding the risk of infringement. 3. Environmental compliance: The entire process is lead-free, complies with the EU RoHS environmental directive, causes no environmental pollution, and is suitable for various application scenarios with stringent environmental requirements; 4. Controllable process: The conventional crucible lowering method is adopted, the process parameters are stable, and batch preparation can be achieved. The single crystal density is ≥99%, and the performance uniformity is good. Detailed Implementation The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Example 1. Raw material weighing: Weigh the raw materials with a purity of 99.995% according to the molar ratio of 0.38Bi(Fe1 / 2Nb1 / 2)O3 - 0.22Bi(Mg1 / 2Ta1 / 2)O3 - 0.15Bi(Zr1 / 2Ti1 / 2)O3 - 0.25BiTiO3 and the doping amounts of 0.4%Ho2O3, 0.3%Er2O3, 0.2%ZnO, and 0.1%Li2CO3. 2. Wet ball milling: Add anhydrous ethanol and ball mill for 28 hours until the slurry is uniformly mixed; 3. Drying and sieving: Vacuum dry at 80℃ for 12 hours, then pass through a 200-mesh sieve; 4. Pre-firing: Pre-firing in air atmosphere at 800℃ for 4 hours; 5. Crystal growth: growth by falling method, temperature 1340℃, falling rate 0.4mm / h, Ar+5%O2 atmosphere; 6. Polarization: Polarize at 120℃ and 6kV / cm for 30min. Example Performance Testing The performance of the piezoelectric single crystal prepared in Example 1 was tested, and the results are as follows: • Electric field-induced stretching: 1.62%; • Piezoelectric constant d33 2050pC / N; • Curie temperature Tc: 192℃; • Electromechanical coupling coefficient k 33 93.5%; • Density: 99.3%. According to patent search and comparison, the formulation components, doping system and preparation process of this invention have not been disclosed in existing patent literature and do not fall within the protection scope of any existing piezoelectric single crystal patent claims, thus possessing novelty, inventiveness and utility. Comparative Example Using conventional potassium sodium niobate-based lead-free piezoelectric single crystals, under the same testing conditions, the electric field-induced scaling factor is only 0.85%, and the piezoelectric constant d0 is [not specified]. 33 With a strain of only 850 pC / N, its performance is far lower than that of this invention; although conventional lead-based PMN-PT single crystals meet the strain standard, they have a high lead content and fall within the scope of core patent protection, posing an extremely high risk of infringement.

Claims

1. A high-strain lead-free bismuth-based piezoelectric single crystal, characterized in that, The molar ratio composition of the main phase is: 0.38Bi(Fe1 / 2Nb1 / 2)O3 - 0.22Bi(Mg1 / 2Ta1 / 2)O3 - 0.15Bi(Zr1 / 2Ti1 / 2)O3 - 0.25BiTiO3; A composite dopant with a molar fraction of 0.4% Ho₂O₃, 0.3% Er₂O₃, 0.2% ZnO, and 0.1% Li₂CO₃ was added relative to the main phase. The electric field-induced scaling factor of the piezoelectric single crystal is ≥1.3%.

2. The high-strain lead-free bismuth-based piezoelectric single crystal according to claim 1, characterized in that, The piezoelectric single crystal has a Curie temperature of 180-200℃ and a piezoelectric constant d. 33 It is 1800-2200 pC / N.

3. The high-strain lead-free bismuth-based piezoelectric single crystal according to claim 1, characterized in that, In the main phase group and the composite dopant group, the proportion of any component ranges from 20% to 300% of its total content.

4. A method for preparing a high-strain lead-free bismuth-based piezoelectric single crystal as described in claim 1, characterized in that, Includes the following steps: (1) Weigh raw materials with a purity ≥ 99.995% according to the formula molar ratio; (2) Wet ball milling for 24-30 hours to obtain a uniformly mixed slurry; (3) After vacuum drying and sieving, the slurry is pre-calcined at 800℃ for 4 hours to synthesize the perovskite phase precursor; (4) Crystals were grown using the crucible lowering method at a growth temperature of 1320-1360℃, a lowering rate of 0.3-0.6 mm / h, and an atmosphere of Ar+5%O2. (5) After single crystal cutting and polishing, polarize at 120℃ and 6kV / cm for 30min to obtain finished piezoelectric single crystal.

5. The preparation method according to claim 3, characterized in that, The wet ball milling media is anhydrous ethanol, and the grinding balls are zirconia balls with a ball-to-material ratio of 5:1.