High-performance relaxor ferroelectric single crystal and preparation method and application thereof

Abstract

The application discloses a high-performance relaxor ferroelectric single crystal and a preparation method and application thereof, and belongs to the technical field of piezoelectric materials. Based on a TSSG method, through the synergistic effect of a bottom oxygen feeding technology and component regulation, a technical problem that a piezoelectric charge coefficient d 33 and a piezoelectric voltage coefficient g 33 are difficult to be considered simultaneously in the existing relaxor ferroelectric single crystal is successfully solved. The bottom oxygen feeding technology effectively inhibits Pb element volatilization and compensates oxygen vacancies, greatly reduces the defect density and the content of impurities in the crystal, and eliminates the pinning effect of defect dipoles on domain switching. In combination with accurate construction of a morphotropic phase boundary, the single crystal can fully release the polarization deflection advantage caused by the coexistence of multiple phases. The prepared PYN-PMN-PT relaxor ferroelectric single crystal realizes the coexistence of high piezoelectric response and excellent piezoelectric voltage coefficient, and significantly improves the quality factor of the material.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric materials technology, and in particular to a high-performance relaxor ferroelectric single crystal, its preparation method, and its application. Background Technology

[0002] Piezoelectric devices play an indispensable role in various fields such as the Internet of Things (IoT), microelectromechanical systems (MEMS), sensors, actuators, and transducers, with applications spanning daily life, healthcare, and the military. The material's quality factor (d) 33 ×g 33 ) is a key indicator for evaluating the performance of piezoelectric materials, and high d 33 ×g 33 This value not only improves the electromechanical response sensitivity but also achieves high energy output density. Among these, the piezoelectric charge coefficient (d...) 33 ) and piezoelectric voltage coefficient (g 33 ) directly affects the electromechanical conversion efficiency of the device, and g 33 It is closely related to the energy output of the piezoelectric energy harvester.

[0003] Relaxorable lead titanate (relaxation-PT) ferroelectric single crystals, such as lead magnesium niobate-lead titanate (PMN-PT) and lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT), possess excellent d-phase properties. 33 Value (approximately 2000 pC / N) and high electromechanical coupling coefficient (k 33 The high doping concentration (>90%) has attracted much attention. Researchers can further improve the d-value by optimizing the doping composition and polarization method. 33 Values, such as those of PMN-PT single crystals doped with samarium (Sm) ions at the A site, include d... 33 The value can exceed 4000 pC / N. However, existing technologies have two major bottlenecks: one is "high d 33 With high g 33 "mutually exclusive", high d 33 Values ​​are often accompanied by a high dielectric constant ε. 33 T / ε0, according to g 33 =d 33 / ε 33 T The relationship, ε 33 T A sharp increase in / ε0 will lead to g 33 The value remains basically unchanged or even decreases, causing the quality factor (d) of relaxor-PT ferroelectric single crystals to remain basically unchanged or even decrease. 33 ×g 33 The value remained at 1.0 × 10 for an extended period. 5 pC mV / (N² The first issue is insufficient temperature stability; the traditional PMN-PT single crystal Curie temperature is approximately 150 °C, and the trigonal-tetragonal phase transition temperature Tm is below 150 °C. RT At approximately 90 ℃, it cannot meet the requirements for high-temperature applications above 100 ℃.

[0004] Those skilled in the art have tried various solutions: A-site doping with La³ + Sm³ + Ions can only enhance d 33 g 33 No significant improvement; B-site doping with Sc³ + In³ + Plasma easily introduces impurities, disrupting crystal integrity; adjusting the PT content can only slightly optimize a single property and cannot achieve d 33 g 33 Synergistic improvement with temperature stability. Although there are existing technologies regarding the utilization of Yb³ + An attempt to construct a PYN-PMN-PT ternary system using ion doping aims to utilize Yb³ + (0.99 Å) Adaptive B-site characteristics can improve performance, but existing Yb doping techniques have failed to effectively control the phase structure ratio and microdomain structure at the quasi-isomorphic phase boundary (MPB), and have not been based on g 33 Starting from the anisotropy, ultra-high g of the semi-tetragonal phase was prepared. 33 Single crystal. Secondly, due to the lattice distortion caused by Yb rare earth doping, single crystal growth becomes difficult, easily leading to defects and oxygen vacancy enrichment. This results in poor quality of existing PYN-PMN-PT single crystals, failing to balance the contradiction between "high voltage activity" and "low dielectric constant". Therefore, the ternary system in the current technology still cannot achieve d 33 With g 33 The synergistic improvement is insufficient to simultaneously meet the requirements of high sensitivity and high figure of merit. Summary of the Invention

[0005] To solve the above problems, this application is approved by Yb³ + Ion doping was used to construct ternary PYN-PMN-PT relaxor ferroelectric single crystals, while the PT content was controlled to maintain a multiphase coexistence state with a bias towards a tetragonal structure. Due to g 33 Anisotropy, its four directions <001> The oriented single crystal exhibits the highest value compared to the R / O phase. Through precise control of multiphase coexistence, d... 33 and g 33 Synergistic improvement. This addresses the difficulty in achieving high quality factors in existing technologies, while also possessing the advantages of high voltage charge coefficient (…). d 33 Up to 1665pC / N), high voltage coefficient (g) 33 Up to 85.2 mV It has excellent dielectric and ferroelectric properties (m / N).

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high-performance relaxor ferroelectric single crystal includes: S1: Weigh and prepare flux and solute materials for PYN-PMN-PT relaxor ferroelectric single crystals according to the nominal chemical composition, wherein the molar ratio of flux and solute materials is 5:1; S2: Provide a PMN-PT single crystal with (001) crystal plane as a seed crystal; S3: Load the molten raw material and fluxing raw material into a crucible and melt them into a mixed melt; S4: The seed crystal is placed in contact with the melt for seeding, and the cooling rate is adjusted according to the nominal chemical composition to allow the crystal to grow. S5: After growth is complete, cool to room temperature and remove the PYN-PMN-PT relaxor ferroelectric single crystal; The crucible is equipped with an oxygen supply device at the bottom, and in steps S3 and S4, the oxygen supply device continuously supplies oxygen to the crucible.

[0007] Furthermore, in step S1, the flux is PbO and H3BO3 in a molar ratio of 5:1.

[0008] Further, step S3 includes: S301: The molten raw material and fluxing raw material are loaded into the crucible; S302: Continuously purge oxygen at a rate of 0.05 L / min, heat the crucible to 1200 ℃ at a rate of 2 ℃ / min, and hold the temperature until the molten raw material and fluxing raw material melt into a mixed melt.

[0009] Further, step S4 includes: S401: Continue to purge oxygen at a rate of 0.05 L / min, cool down to 1050 ℃ at a rate of 1 ℃ / min, and maintain the temperature for the predetermined time; S402: The seed crystal is brought into contact with the melt for seeding, and the seeding process is observed and the temperature is adjusted in real time; S403: After successful inoculation, the oxygenation rate is 0.1-0.2 L / min, and the cooling rate is adjusted according to the nominal chemical composition to promote crystal growth.

[0010] Furthermore, in step S402, the inoculation situation is observed in real time, and when the crystal outline appears at the bottom of the seed crystal, the inoculation is confirmed to be successful. If no crystal outline is observed after the seed crystal has been in contact with the melt for 30 minutes, the temperature is gradually reduced by 5 °C and each time is waited for 30 minutes until successful seeding.

[0011] Furthermore, in step S403, the cooling rate is controlled at 0.4-0.8 ℃ / h; Specifically, when the PbTiO3 content x in the nominal chemical composition satisfies 0.37 ≤ x ≤ 0.40, the cooling rate is controlled at 0.5-0.8 ℃ / h; when x satisfies 0.43 ≤ x ≤ 0.46, the cooling rate is controlled at 0.4-0.6 ℃ / h.

[0012] Further, step S5 includes: S501: After the temperature drops to 900 ℃, stop cooling and oxygenation; S502: After cooling at a rate of 20 ℃ / h, the PYN-PMN-PT relaxor ferroelectric single crystal is removed.

[0013] This application also provides a high-performance relaxor ferroelectric single crystal, prepared using the preparation method described above; its chemical composition is 0.15Pb(Yb1 / 2Nb1 / 2)O3-(0.85-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3, wherein 0.37 ≤ x ≤ 0.46.

[0014] Furthermore, the piezoelectric charge coefficient d 33 890-2235 pC / N; piezoelectric voltage coefficient g 33 The voltage range is 52.43-85.2 mV. m / N.

[0015] This application also provides the application of the high-performance relaxor ferroelectric single crystals described above in the fabrication of piezoelectric devices.

[0016] In summary, this application has the following beneficial effects: 1. This application successfully solves the problem of the piezoelectric charge coefficient d in existing relaxor ferroelectric single crystals by utilizing the synergistic effect of bottom oxygen-permeable TSSG growth technology and composition control. 33 With piezoelectric voltage coefficient g 33 The technical challenge of achieving both objectives simultaneously was significant. Continuous oxygen permeation at the bottom effectively suppressed Pb volatilization and compensated for oxygen vacancies, substantially reducing the defect density and impurity phase content within the crystal, and eliminating the pinning effect of defect dipoles on domain reversal. Based on this high crystal quality, combined with the precise construction of quasi-isomorphic phase boundaries, the single crystal could fully leverage the advantages of highly sensitive polarization reversal resulting from multiphase coexistence. Ultimately, the prepared PYN-PMN-PT relaxor ferroelectric single crystal achieved an ultra-high voltage electric response (d...). 33 Up to 1665 pC / N) and excellent piezoelectric voltage coefficient (g 33 The coexistence of up to 85.2 mV·m / N significantly improves the material's quality factor.

[0017] 2. This application establishes a differentiated cooling rate control strategy. This is particularly relevant for high-g environments. 33 The tetragonal phase, a dominant component, is effectively balanced by inhibited slow growth (0.4-0.6 ℃ / h) and dynamic feedback regulation, thus avoiding component overcooling and inclusion defects caused by excessively rapid crystallization. This refined process control significantly improves the success rate of single crystal growth and bulk utilization.

[0018] 3. The PYN-PMN-PT relaxor ferroelectric single crystal prepared in this application not only has a high Curie temperature and phase transition temperature, but also exhibits excellent coercive field characteristics. This combination of high thermal stability and high breakdown resistance makes it less prone to thermal depolarization or electrical breakdown under harsh environments such as high temperature and high electric field, effectively meeting the long-term reliability requirements of piezoelectric devices in extreme scenarios such as automotive engine monitoring and deep well exploration. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the TSSG top seed crystal oxygen furnace structure used in the preparation method of this application; wherein, 1, rotating device; 2, control thermocouple; 3, alumina wire rod; 4, platinum crucible; 5, PYN-PMN-PT single crystal; 6, alumina tube; 7, gas tube; 8, adjustable support; Figure 2 This application shows the PYN-PMN-PT single crystal blank and its orientation along the (001) plane; wherein, (a) Photograph of a single crystal blank with a strength of 0.15PYN-0.48PMN-0.37PT; (b) Photograph of a single crystal blank with a crystal density of 0.15PYN-0.45PMN-0.40PT; (c) Photograph of a single crystal blank with a crystal density of 0.15PYN-0.42PMN-0.43PT; (d) is a photograph of a single-crystal blank with a crystal density of 0.15PYN-0.39PMN-0.46PT; (e) is the XRD pattern of the (001) plane of a single crystal; Figure 3 The images show the X-ray diffraction (XRD) patterns of the PYN-PMN-PT relaxor ferroelectric single crystals of this application; where (a) is the 15-80° XRD pattern, (b) is a magnified view of the (111) crystal plane diffraction peak, and (c) is a magnified view of the (111) crystal plane diffraction peak. Figure 4The XRD patterns of the single crystal composition near MPB in this application are refined; where (a) is the 0.15PYN-0.42PMN-0.43PT composition and (b) is the 0.15PYN-0.45PMN-0.4PT composition. Figure 5 This is a schematic diagram showing the distribution of the nominal composition of the PYN-PMN-PT relaxor ferroelectric single crystal and the actual composition measured using an EPMA (electron probe microanalyzer) in the ternary phase diagram. Figure 6 The dielectric properties of the PYN-PMN-PT relaxor ferroelectric single crystal of this application are shown in the spectrum; where (a)-(d) are the dielectric constant and dielectric loss temperature spectra of different components. Figure 7 The graphs show the ferroelectric properties of the PYN-PMN-PT relaxor ferroelectric single crystal in this application; where (a) is the hysteresis loop, (b) is the strain curve, and (c) is the remanent polarization (P). ) and coercive field (E C (d) is a comparison chart of strain values; Figure 8 Temperature-dependent piezoelectric performance testing of PYN-PMN-PT relaxor ferroelectric single crystals for this application; wherein, (a) is the temperature-dependent piezoelectric performance testing of 0.15PYN-0.45PMN-0.40PT. 33 Test; (b) is for high g 33 Components: 0.15PYN - 0.42PMN - 0.43PT (temperature variation) 33 test; Figure 9 This application relates to the g of PYN-PMN-PT relaxor ferroelectric single crystal. 33 Performance comparison chart with other ferroelectric single crystals and ceramics. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] Example 1 This embodiment provides a high-performance relaxor ferroelectric single crystal and its preparation method, the preparation method including: S1: Weigh and prepare flux and solute materials for PYN-PMN-PT relaxor ferroelectric single crystals according to the nominal chemical composition, wherein the molar ratio of flux and solute materials is 5:1; S2: Provide a PMN-PT single crystal with (001) crystal plane as a seed crystal; S3: Load the molten raw material and fluxing raw material into a crucible and melt them into a mixed melt; S4: The seed crystal is placed in contact with the melt for seeding, and the cooling rate is adjusted according to the nominal chemical composition to allow the crystal to grow. S5: After growth is complete, cool to room temperature and remove the PYN-PMN-PT relaxor ferroelectric single crystal; The crucible is equipped with an oxygen supply device at the bottom, and in steps S3 and S4, the oxygen supply device continuously supplies oxygen to the crucible.

[0022] Specifically, it includes the following steps: 1. Raw material preparation: Accurately weigh the starting materials according to the nominal chemical composition 0.15PYN-(0.85-x)PMN-xPT (x=0.37, 0.40, 0.43, 0.46). The purity requirements for the raw materials are: PbO ≥ 99.99%, TiO2 ≥ 99.90%, MgO ≥ 99.90%, Nb2O5 ≥ 99.90%, Yb2O3 ≥ 99.99%, H3BO3 ≥ 99.90%, ensuring that no impurities are introduced into the raw materials to avoid affecting the purity of the single crystal. The weighing accuracy is controlled within ±0.001 g to ensure the accuracy of the stoichiometry.

[0023] The weighed raw materials were placed in a 100℃ oven and dried for 12 hours to obtain uniformly dried growth powder, thus avoiding powder agglomeration that could lead to incomplete melting.

[0024] 2. Preparation of flux and flux raw materials: PbO and H3BO3 were mixed in a molar ratio of 5:1 and ground in an agate mortar for 20 minutes until fully mixed, serving as a high-temperature fluxing agent. The molar ratio of the fluxing agent to the solute (i.e., a mixture of PYN, PMN, and PT) was strictly controlled at 5:1. This ratio lowers the melting temperature of the raw materials, ensures that all components are fully dissolved, forms a homogeneous melt, and provides a stable solute supply environment for single crystal growth.

[0025] It should be noted that if the inoculation temperature needs to be increased (e.g., to prevent the formation of the pyrochlore phase at low temperatures), the flux to solute molar ratio can be adjusted to 3:1, but the inoculation temperature must be increased to 1080-1100 ℃ simultaneously, and the cooling rate should be appropriately reduced (0.3-0.5 ℃ / h) to ensure normal crystal growth.

[0026] 3. Seed crystal pretreatment: A PMN-PT single crystal with a (001) crystal plane was selected as the seed crystal. The seed crystal size was controlled to be 3mm×3mm×20mm. The accuracy of the seed crystal plane orientation was verified by X-ray diffraction (XRD). The test conditions were: Cu-Kα radiation, scanning step size 0.02°, angle range 10-80°. The intensity ratio of the (100) and (200) diffraction peaks corresponding to the (001) crystal plane was ≥ 95%, so as to avoid the crystal growth direction shift caused by the crystal plane orientation deviation.

[0027] The seed crystal is vertically bound to the end of the alumina tube using platinum wire with a diameter of 0.3 mm or 0.5 mm. The binding position is 5 mm away from the bottom of the seed crystal. During the binding process, an optical microscope is used to observe and ensure that the axis of the seed crystal coincides with the axis of the alumina tube, with a verticality deviation of ≤ 0.5°. This avoids the seed crystal tilting, which could cause it to touch the crucible wall during crystal growth and generate stress defects.

[0028] 4. Crystal growth: This step is the core of the preparation method, employing the top seed crystal method (TSSG) combined with a bottom oxygenation process. The growth cycle is 10-15 days, and the specific operation is as follows: (1) Loading the furnace: Load the mixed growth powder (melting material and fluxing material) into a Φ40×40 mm² Pt crucible, controlling the loading height to 25-27 mm (not exceeding 2 / 3 of the crucible height) to prevent the melt from overflowing after melting. Set an oxygen conduit at the bottom of the Pt crucible, with the end of the conduit 5 mm away from the bottom of the crucible to ensure that oxygen diffuses evenly into the melt; place the center of the Pt crucible containing the powder on the bottom oxygen conduit of the tube furnace. Fix the alumina tube with the seed crystal tied to it on the lifting device at the top of the furnace body, aligning it directly above the center of the crucible, initially 50 mm away from the crucible opening.

[0029] (2) Heating and melting: Start the tubular furnace and simultaneously turn on the bottom oxygen supply device to introduce oxygen with a purity of ≥ 99%. The oxygen supply rate is controlled at 0.05 L / min. Continuous oxygen supply is maintained throughout the process to suppress the high-temperature volatilization of Pb and optimize the oxidative environment of the melt. Heat from room temperature to 1200 ℃ at a rate of 2℃ / min. After reaching 1200 ℃, hold at that temperature for 10 hours to allow the powder to fully melt and form a uniform melt.

[0030] (3) Cooling and inoculation: After the heat preservation is completed, keep the oxygen flow rate constant and cool down to 1050 ℃ (inoculation start temperature) at a rate of 1 ℃ / min, and keep this temperature constant for 30 minutes. Slowly lower the seed crystal through the lifting device so that the bottom of the seed crystal is immersed 2-3 mm below the surface of the melt to start inoculation. During the inoculation process, observe the contact state between the seed crystal and the melt in real time through the observation hole. When a clear and continuous crystal outline appears at the bottom of the seed crystal, the inoculation is confirmed to be successful. If no crystal outline appears after 30 minutes, reduce the temperature appropriately (5 ℃ each time and wait for 30 min) until the inoculation is successful. Avoid rate fluctuations during the oxygen flow process to prevent melt convection turbulence.

[0031] (4) Crystal growth: After successful inoculation, maintain the oxygen flow rate at 0.1-0.2 L / min and start the cooling program, slowly cooling from 1050 ℃ to 900 ℃ at a rate of 0.4-0.8 ℃ / h. The cooling rate is adjusted according to the crystal composition: 0.5-0.8 ℃ / h for x = 0.37 and 0.40 (rhombohedral phase and components near MPB), and 0.4-0.6 ℃ / h for x = 0.43 and 0.46 (tetragonal phase and components near MPB). Through the synergistic effect of "oxygen environment + slow cooling", the supersaturation and compositional homogeneity of the melt are maintained, the nucleation of PbO impurity phase is suppressed, and the directional growth of crystal is promoted. During the growth process, the oxygen flow rate can be finely adjusted to 0.1 L / min according to the crystal surface state (after the appearance of a square outline) to further optimize the impurity phase suppression effect.

[0032] (5) Crystal Removal: When the temperature drops to 900 ℃, stop the cooling process, shut off the oxygen supply system, and start the cooling process to cool to room temperature at a rate of 20 ℃ / h. Keep the seed crystal fixed during the cooling process to avoid cracking of the crystal due to thermal stress. Wait for the furnace to cool naturally to below 50 ℃, open the furnace, and remove the Pt crucible.

[0033] 5. Sample post-processing: (1) Cutting orientation: The single crystal blank is sliced ​​along the (001) direction using a diamond slicing machine. The slice thickness is controlled to be 0.5-2 mm according to the application requirements. After cutting, the crystal plane of the slice is verified by X-ray orientation scanning. The test conditions are the same as those for seed crystal verification to ensure that the diffraction peak of the (001) plane corresponds to the (100) and (200) crystal planes, and the orientation accuracy deviation is ≤ 0.1°.

[0034] (2) Polishing and cleaning: Polish the slices sequentially with diamond abrasive paper of 400 mesh, 800 mesh, 1200 mesh and 2000 mesh to ensure a smooth surface. After each polishing, place the slices in anhydrous ethanol for ultrasonic cleaning for 10 minutes to remove residual abrasive powder from the surface.

[0035] (3) Electrode preparation: Silver paste (silver content ≥ 99.9%) was uniformly coated on the upper and lower surfaces of the polished crystal using screen printing. The coating thickness was 5-10 μm to ensure that the electrode covered the entire crystal surface without any omissions. The crystal coated with silver paste was placed in a muffle furnace and heated to 550 °C at a rate of 5 °C / min, and held for 30 minutes to sinter the silver paste into a dense state. Then, it was cooled to room temperature at a rate of 3 °C / min to avoid the electrode from falling off or cracking due to excessively rapid cooling.

[0036] (4) Polarization treatment: Place the crystal with electrodes into silicone oil and apply an external electric field of 5-15 kV / cm through a high-voltage power supply. The electric field strength is adjusted according to the crystal thickness: 5-10 kV / cm for a thickness of 0.5-1 mm, and 10-15 kV / cm for a thickness of 1-2 mm. The polarization time is 15 minutes. After polarization, slowly reduce the electric field to zero (the voltage reduction rate is 1 kV / cm). (min) to avoid crystal depolarization caused by sudden changes in electric field, and obtain single crystal samples.

[0037] In some embodiments, the PYN-PMN-PT relaxor ferroelectric single crystal of this application can be prepared according to the specific steps described above. The nominal chemical composition is 0.15Pb(Yb1 / 2Nb1 / 2)O3-(0.85-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3 (where x ranges from 0.37 to 0.46), and the actual chemical composition is 0.12PYN-yPMN-(0.88-y)PT (where y ranges from 0.43 to 0.54). The crystal has a high-purity perovskite phase structure, without any impurity or secondary phase precipitation. + Ions were successfully embedded in the B sites of the ABO3 perovskite lattice composed of PMN-PT in a preferred manner, forming a stable doped solid solution structure without causing lattice distortion or defect aggregation.

[0038] The phase structure, composition, dielectric properties, ferroelectric properties, and piezoelectric properties of the finished single-crystal samples were tested: X-ray diffraction (XRD) was used to analyze the phase structure, confirming the pure perovskite phase; electron probe microanalysis (EPMA) was used to test the actual chemical composition, verifying the Yb³ phase. + Doping effect; room temperature dielectric constant (ε) was measured using a dielectric temperature spectrometer. ) and dielectric loss (tan δ); hysteresis loop and hysteresis strain at room temperature and varying temperature were measured using a ferroelectric analyzer to obtain residual polarization (P Coercive field (E) C ) and ferroelectric temperature stability index; the piezoelectric charge coefficient (d) was tested using a piezoelectric coefficient tester. 33 ) and piezoelectric voltage coefficient (g33 ).

[0039] The core parameters are as follows: piezoelectric charge coefficient d 33 The value is 890-2235 pC / N, of which the nominal composition is 0.15PYN-0.45PMN-0.4PT. 33 The value is the highest, reaching 2235 pC / N; the piezoelectric voltage coefficient g 33 The voltage range is 52.43-85.2 mV. m / N, also nominally composed of 0.15PYN-0.45PMN-0.4PT g 33 The optimal value was achieved, reaching 85.2 mV. m / N; room temperature dielectric constant ε The dielectric loss is low, ranging from 1918 to 3739 (at 1 kHz); the Curie temperature T0 is also low. C The trigonal-tetragonal phase transition temperature T is 176-234 ℃. RT The temperature range is 110-117 ℃ (the phase transition temperature of the semi-tetragonal single crystal is near room temperature), which is higher than that of traditional PMN-PT single crystals (T). C ~150℃, T RT ~90 ℃).

[0040] Example 2 This embodiment provides specific preparation and testing results of PYN-PMN-PT relaxor ferroelectric single crystals.

[0041] The specific preparation method is as described in Example 1. The nominal compositions are given below: E1: 0.15PYN-0.48PMN-0.37PT; E2: 0.15PYN-0.45PMN-0.4PT; E3: 0.15PYN-0.42PMN-0.43PT; E4: 0.15PYN-0.39PMN-0.46PT.

[0042] Reference Figures 1 to 9 ,in: Figure 1This is a schematic diagram of the TSSG top-seeded oxygen furnace structure, which uses a bottom-oxygenation method to grow single crystals. A platinum crucible 4 for holding the mixed powder and molten mixture is located at the center of the furnace. Below the platinum crucible 4 is an alumina tube 6, whose bottom is supported by an adjustable bracket 8, used to stably support the platinum crucible 4 and adjust its height within the furnace chamber. A gas pipe 7 is connected to the bottom of the platinum crucible 4. The gas pipe 7 passes through the internal channel of the alumina tube 6 from bottom to top, extending its end near the bottom of the platinum crucible 4, for continuously introducing oxygen into the molten mixture. A rotating device 1 is located at the top of the furnace, directly above the platinum crucible 4. The rotating device 1 is connected to a vertically downward-extending alumina wire rod 3, with the seed crystal and the grown PYN-PMN-PT single crystal 5 fixed to the bottom end of the alumina wire rod 3. The rotating device 1 drives the alumina wire rod 3 to rise, fall, and rotate, thereby controlling the seeding and pulling growth process of the single crystal. In addition, a control thermocouple 2 is installed next to the heating zone inside the furnace to monitor and provide feedback on temperature changes inside the furnace in real time, so as to cooperate with the precise execution of the cooling program during the growth process.

[0043] Figure 2 The images show the blanks of the PYN-PMN-PT relaxor ferroelectric single crystals of the above compositions. Square crystals can be observed, which are standard perovskite crystals. <001> The material was grown in a specific direction. XRD was used to orient it to obtain two diffraction peaks, (100) and (200), which correspond to the (001) plane.

[0044] Figure 3 The X-ray diffraction (XRD) pattern of the PYN-PMN-PT relaxor ferroelectric single crystal transitioning from trigonal to tetragonal phase is shown. From the magnified view of the (111) crystal plane diffraction peak, it can be seen that Yb doping changes the lattice constant. The magnified view of the (200) crystal plane diffraction peak shows the reaction phase structure, with a single peak indicating a trigonal phase and a split peak indicating a tetragonal phase structure.

[0045] Figure 4 These are crystals of the 0.15PYN-0.45PMN-0.40PT and 0.15PYN-0.42PMN-0.43PT fractions, refined by XRD using Profull software. The corresponding trigonal to tetragonal phase ratios are 95:5 and 39:61, respectively, indicating that these two fractions exhibit excellent electrical properties around MPB.

[0046] Figure 5 The nominal composition in the PYN-PMN-PT relaxor ferroelectric single crystal phase diagram and the actual composition of the crystal measured by EPMA are shown. The black dashed line represents the theoretical MPB region. It can be seen that the actual Yb and Ti content of the crystal is lower than the designed composition, and the segregation coefficient is about 92%, which is within a reasonable range.

[0047] Figure 6 The dielectric properties of the PYN-PMN-PT relaxor ferroelectric single crystals of the above compositions are shown in the graphs. It is evident here that the Yb-doped crystal has a relatively low dielectric constant and a high Tk. C and T RT Furthermore, the dielectric peak shifts towards higher temperatures with increasing Ti content, which also indicates a change in phase structure.

[0048] Figure 7 The images show the ferroelectric properties of the PYN-PMN-PT relaxor ferroelectric single crystals of this application; in (a), the hysteresis loop becomes wider with increasing Ti content, and the coercive field and spontaneous polarization also increase continuously. From the strain curves of each crystal, it can be seen that the 0.15PYN-0.45PMN-0.4PT composition has the largest strain, corresponding to the largest piezoelectric coefficient d. 33 .

[0049] Figure 8 For 0.15PYN-0.45PMN-0.40PT and high g 33 Components: 0.15PYN - 0.42PMN - 0.43PT (temperature variation) 33 The test results in this figure further illustrate that the Yb-doped crystal has a higher temperature, and that the depolarization temperature and Curie temperature correspond to the dielectric temperature spectrum.

[0050] Figure 9 The g of the PYN-PMN-PT single crystal of the present invention 33 Comparison with other ferroelectric single crystals and ceramics shows that the Yb-doped PMN-PT prepared according to the method of this application exhibits higher g-values ​​than currently known relaxor ferroelectric single crystals. 33 value.

[0051] 1. Preparation and performance testing of 0.15PYN-0.48PMN-0.37PT single crystal (denoted as E1) (1) Weighing raw materials: Weigh the raw materials according to the nominal composition 0.15PYN-0.48PMN-0.37PT, including PbO5 0.000g, TiO2 7.402g, MgO 4.801g, Nb2O5 25.603g, Yb2O3 2.300g, and H3BO3 5.901g.

[0052] (2) Raw material pretreatment: The above raw materials were placed in an oven at 100 ℃ and dried for 12 hours. Then, they were placed in an agate mortar, 20 mL of anhydrous ethanol was added, and the mixture was ground for 30 minutes. The mixture was then dried at 80 ℃ for 1 hour to obtain growth powder.

[0053] (3) Flux preparation: PbO and H3BO3 are mixed in a molar ratio of 5:1 and ground for 20 minutes to obtain the flux. The molar ratio of flux to solute is 5:1.

[0054] (4) Seed crystal pretreatment: Select a 3 mm × 3 mm × 20 mm (001) crystal plane PMN-PT seed crystal. After XRD verification that the orientation is qualified, polish, ultrasonically clean, and blow dry. Then, use 0.3 mm platinum wire to vertically bind it to the alumina tube.

[0055] (5) Crystal growth: 1) Loading the furnace: Load the growth powder into a Φ40×40 mm² Pt crucible, place it in the center of the tube furnace, adjust the seed crystal to align with the center of the crucible, and turn on the oxygen supply system with an oxygen flow rate of 0.05 L / min. 2) Heating and melting: Heat to 1200 ℃ at 2 ℃ / min and hold for 10 hours.

[0056] 3) Cooling and inoculation: Cool down to 1050 ℃ at 1 ℃ / min, keep the temperature constant for 30 minutes, and lower the seed crystal to immerse it in the melt by 2 mm. Inoculation is successful.

[0057] 4) Crystal growth: The temperature was reduced to 900 ℃ at a rate of 0.5 ℃ / h, the seed crystal rotation speed was gradually increased from 6 r / min to 8 r / min, the growth cycle was 7 days, and the oxygen flow rate was increased to 0.1-0.2 L / min.

[0058] 5) Cooling and removing: Cool to room temperature at 20 ℃ / h and remove the single crystal blank.

[0059] (6) Sample post-processing: Cut into 1 mm thick slices along the (001) direction, polish, coat with silver paste and sinter at 550 °C for 30 minutes, and polarize in silicone oil at room temperature under an electric field of 10 kV / cm for 15 minutes.

[0060] (7) Performance testing: The actual composition of this single crystal is 0.12PYN-0.54PMN-0.34PT, and the phase structure is rhombohedral phase (R); d 33 =1650 pC / N, ε =3293 (25 ℃, 1 kHz), g 33 =56.62 mV m / N, T C =176 ℃, T RT =110 ℃; the hysteresis loop exhibits typical saturation characteristics, and the residual polarization P =26.7 μC / cm², coercive field E C =3.82 kV / cm.

[0061] 2. Preparation and performance testing of 0.15PYN-0.45PMN-0.4PT single crystal (denoted as E2) (1) Weighing raw materials: Weigh the raw materials according to the nominal composition 0.15PYN-0.45PMN-0.4PT, including PbO 50.000g, TiO2 8.001g, MgO 4.500g, Nb2O5 24.002g, Yb2O3 2.300g, and H3BO3 5.901g.

[0062] (2) The steps for raw material pretreatment, flux preparation and seed crystal pretreatment are the same as in E1.

[0063] (3) Crystal growth: 1) The steps of loading the furnace, heating and melting, cooling and inoculating, and oxygenation are the same as in E1.

[0064] 2) Crystal growth: The temperature was lowered to 900 ℃ at a rate of 0.4-0.6 ℃ / h, the seed crystal rotation speed was gradually increased from 6 r / min to 8 r / min, and oxygen was introduced at a rate of 0.1-0.2 L / min for a growth cycle of 7 days.

[0065] 3) The cooling and removal steps are the same as in E1.

[0066] (4) Sample post-processing: The slice thickness is 1 mm, and the polarization conditions are 15 minutes under a 10 kV / cm electric field at room temperature. The remaining steps are the same as E1.

[0067] (5) Performance testing: The actual composition of this single crystal is 0.12PYN-0.51PMN-0.37PT, and the phase structure is R phase: T phase = 95:5 (MPB region); d 33 =2235 pC / N, ε =3739 (25 ℃, 1 kHz), g 33 =67.39 mV m / N, T C =184 ℃, T RT =117 ℃; hysteresis loop saturation, P =29.4 μC / cm², E C =4.99 kV / cm; the strain value is the highest among the four components, indicating excellent thermal stability.

[0068] 3. Preparation and performance testing of 0.15PYN-0.42PMN-0.43PT single crystal (denoted as E3) (1) Weighing raw materials: Weigh the raw materials according to the nominal composition 0.15PYN-0.42PMN-0.43PT, including PbO 50.000g, TiO2 8.601g, MgO 4.200g, Nb2O5 22.402g, Yb2O3 2.300g, and H3BO3 5.901g.

[0069] (2) The steps for raw material pretreatment, flux preparation and seed crystal pretreatment are the same as in E1.

[0070] (3) Crystal growth: 1) The steps of loading the furnace, heating and melting, and cooling and inoculating are the same as in E1.

[0071] 2) Crystal growth: The temperature was lowered to 900 ℃ at a rate of 0.4-0.5 ℃ / h, the seed crystal rotation speed was gradually increased from 6 r / min to 8 r / min, and oxygen was introduced at a rate of 0.1-0.2 L / min for a growth cycle of 7 days.

[0072] 3) The cooling and removal steps are the same as in E1.

[0073] (4) Sample post-processing: The slice thickness is 1 mm, and the polarization conditions are 15 kV / cm electric field at room temperature for 15 minutes. The remaining steps are the same as E1.

[0074] (5) Performance testing: The actual composition of this single crystal is 0.12PYN-0.47PMN-0.41PT, and the phase structure is R phase: T phase = 39:61 (MPB region); d 33 =1680 pC / N, ε =2228 (25 ℃, 1 kHz), g 33 =85.2 mV m / N, T C =203 ℃; P =33.75 μC / cm², E C =6.85 kV / cm.

[0075] 4. Preparation and performance testing of 0.15PYN-0.39PMN-0.46PT single crystal (extremely E4). (1) Weighing raw materials: Weigh the raw materials according to the nominal composition 0.15PYN-0.39PMN-0.46PT, including PbO 50.000g, TiO2 9.201g, MgO 3.900g, Nb2O5 20.802g, Yb2O3 2.300g, and H3BO3 5.901g.

[0076] (2) The steps for raw material pretreatment, flux preparation and seed crystal pretreatment are the same as in E1.

[0077] (3) Crystal growth: 1) The steps of loading the furnace, heating and melting, and cooling and inoculating are the same as in E1.

[0078] 2) Crystal growth: The temperature was lowered to 900 ℃ at a rate of 0.3-0.5 ℃ / h, the seed crystal rotation speed was gradually increased from 6 r / min to 8 r / min, and oxygen was introduced at a rate of 0.1-0.2 L / min for a growth cycle of 8 days.

[0079] 3) The cooling and removal steps are the same as in E1.

[0080] (4) Sample post-processing: The slice thickness is 1 mm, and the polarization conditions are 15 kV / cm electric field at room temperature for 15 minutes. The remaining steps are the same as E1.

[0081] (5) Performance testing: The actual composition of this single crystal is 0.12PYN-0.43PMN-0.45PT, and the phase structure is tetragonal (T); d 33 =890 pC / N, ε =1918 (25 ℃, 1 kHz), g 33 =52.43 mV m / N, T C =234 ℃, no obvious T RT ;P =37.35 μC / cm², E C =10.02 kV / cm, with strong resistance to penetration.

[0082] As can be seen from the above performance tests, the PYN-PMN-PT relaxor ferroelectric single crystal prepared by the method of this application exhibits excellent performance, especially the components (E2 and E3) in the MPB region, which also possess high d 33 and high g 33 The quality factor is outstanding. The preparation method effectively solves problems such as impurity phase encapsulation, component segregation, and orientation shift that exist in traditional growth processes through refined process control. The process is stable and reliable, suitable for industrial production, and has broad application prospects.

[0083] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-performance relaxor ferroelectric single crystal, characterized in that, include: S1: Weigh and prepare flux and solute materials for PYN-PMN-PT relaxor ferroelectric single crystals according to the nominal chemical composition, wherein the molar ratio of flux and solute materials is 5:1; S2: Provide a PMN-PT single crystal with (001) crystal plane as a seed crystal; S3: Load the molten raw material and fluxing raw material into a crucible and melt them into a mixed melt; S4: The seed crystal is placed in contact with the melt for seeding, and the cooling rate is adjusted according to the nominal chemical composition to allow the crystal to grow. S5: After growth, cool to room temperature and remove the PYN-PMN-PT relaxor ferroelectric single crystal. The chemical composition of the PYN-PMN-PT relaxor ferroelectric single crystal is 0.15Pb(Yb1 / 2Nb1 / 2)O3-(0.85-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3, where 0.37 ≤ x ≤ 0.

46. Among them, an oxygen supply device is provided at the bottom of the crucible, and in steps S3 and S4, the oxygen supply device continuously supplies oxygen to the crucible. In step S1, the flux is PbO and H3BO3 in a molar ratio of 5:1; Step S3 includes: S301: The molten raw material and fluxing raw material are loaded into the crucible; S302: Continuously purge oxygen at a rate of 0.05 L / min, heat the crucible to 1200 ℃ at a rate of 2 ℃ / min, and hold the temperature until the molten raw material and fluxing raw material melt into a mixed melt; Step S4 includes: S401: Continue to purge oxygen at a rate of 0.05 L / min, cool down to 1050 ℃ at a rate of 1 ℃ / min, and maintain the temperature for the predetermined time; S402: Inoculate the seed crystal into the melt, observe the inoculation process in real time and adjust the temperature accordingly; S403: After successful inoculation, the oxygenation rate is 0.1-0.2 L / min, and the cooling rate is adjusted according to the nominal chemical composition to promote crystal growth; In step S403, the cooling rate is controlled at 0.4-0.8 ℃ / h; Specifically, when the PbTiO3 content x in the nominal chemical composition satisfies 0.37 ≤ x ≤ 0.40, the cooling rate is controlled at 0.5-0.8 ℃ / h; when x satisfies 0.43 ≤ x ≤ 0.46, the cooling rate is controlled at 0.4-0.6 ℃ / h.

2. The method for preparing high-performance relaxor ferroelectric single crystals according to claim 1, characterized in that, In step S402, the inoculation process is observed in real time. When the crystal outline appears at the bottom of the seed crystal, the inoculation is confirmed to be successful. If no crystal outline is observed after the seed crystal has been in contact with the melt for 30 minutes, the temperature is gradually reduced by 5 °C and each time is waited for 30 minutes until successful seeding.

3. The method for preparing high-performance relaxor ferroelectric single crystals according to claim 1, characterized in that, Step S5 includes: S501: After the temperature drops to 900 ℃, stop cooling and oxygenation; S502: After cooling at a rate of 20 ℃ / h, the PYN-PMN-PT relaxor ferroelectric single crystal is taken out.

4. A high-performance relaxor ferroelectric single crystal, characterized in that, Prepared using the preparation method described in any one of claims 1-3.

5. The high-performance relaxor ferroelectric single crystal according to claim 4, characterized in that, piezoelectric charge coefficient d 33 890-2235 pC / N; piezoelectric voltage coefficient g 33 The voltage range is 52.43-85.2 mV. m / N.

6. The application of the high-performance relaxor ferroelectric single crystal as described in claim 5 in the fabrication of piezoelectric devices.

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