A method for inhibiting depolarization of a three-phase relaxation ferroelectric single crystal based on interface modification

Abstract

The application relates to the technical field of piezoelectric materials, and discloses a method for inhibiting depolarization of a trigonal phase relaxor ferroelectric single crystal based on interface modification, which comprises single crystal pretreatment, polarization electric field optimization, interface modification layer construction, gradient annealing treatment, stable electric field application and protective layer packaging. Through single crystal pretreatment and polarization electric field optimization, the surface of the single crystal is ensured to be smooth and clean, a step-by-step boosting method is adopted to apply a main polarization electric field in a protective atmosphere, oxidation damage of the single crystal is avoided, and the polarization effect is improved, thereby laying a foundation for inhibiting depolarization. Through interface modification layer construction and gradient annealing treatment, a high dielectric constant interface layer is formed on the surface of the single crystal, internal stress is eliminated in a protective atmosphere through multi-stage program temperature annealing, the interface bonding strength and the crystal structure stability are enhanced, and the depolarization process is inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of piezoelectric materials, in particular to a method for inhibiting depolarization of rhombohedral relaxor ferroelectric single crystals based on interface modification. BACKGROUND

[0002] Water acoustic transducers are usually driven by piezoelectric materials such as lead zirconate titanate polycrystalline piezoelectric ceramic materials, relaxor ferroelectric single crystals, or piezoelectric ceramic-polymer composites. As the front end of the sonar system, water acoustic transducers undertake the task of transmitting and receiving sound waves, and are widely used in ship and submarine sonar, ocean resource exploration, environmental protection, and medical equipment fields.

[0003] At present, in the polarization process of rhombohedral relaxor ferroelectric single crystals, due to the lack of fine control of the surface state of the single crystal and the optimization of the polarization electric field parameters, the interface stability of the single crystal is insufficient after polarization. At the same time, the conventional annealing treatment cannot effectively eliminate the internal stress, and lacks subsequent stabilization measures, so that the single crystal is prone to depolarization under long-term use or environmental changes, affecting the stability of its piezoelectric properties.

[0004] Therefore, the present application provides a method for inhibiting depolarization of rhombohedral relaxor ferroelectric single crystals based on interface modification to solve the above problems.

[0005] In this application, the standard symbol rules in material science and crystallography are used:

[0006] Crystal direction: represented by square brackets, for example

[001] . This represents a specific direction.

[0007] Crystal plane: represented by round brackets, for example (001). This represents a specific plane.

[0008] Crystal direction family: represented by angle brackets, for example <001>. This represents the set of all directions that are equivalent to each other by crystal symmetry, for example in the cubic system, the <001> family includes

[001] ,

[010] ,

[100] , [00-1], [0-10], [-100] and other directions. SUMMARY

[0009] In view of the deficiencies of the prior art, the present application provides a method for inhibiting depolarization of rhombohedral relaxor ferroelectric single crystals based on interface modification, which solves the problems of insufficient interface stability of the single crystal after polarization, easy occurrence of depolarization of the single crystal under long-term use or environmental changes, and affects the stability of its piezoelectric properties.

[0010] To achieve the above purpose, the present application provides the following technical solution: a method for inhibiting depolarization of rhombohedral relaxor ferroelectric single crystals based on interface modification, comprising the following steps:

[0011] Step one: single crystal pretreatment, select rhombohedral phase relaxor ferroelectric single crystal, surface polishing, cleaning and drying;

[0012] Step two: polarization field optimization, the pretreated single crystal is placed in a controllable temperature polarization device, a main polarization field with a field strength of 0.5-3.0 kV / mm is applied along its spontaneous polarization direction, the polarization temperature is 80-150℃, and the polarization time is 10-60 minutes;

[0013] Step three: interface modification layer construction, a 10-500 nanometer thick interface modification layer is prepared on the surface of the polarized single crystal;

[0014] Step four: gradient annealing treatment, the single crystal is placed in a program-controlled temperature furnace for multi-stage gradient annealing, first heated to 200-300℃ at a rate of 1-5℃ / min and kept for 30-90 minutes, then cooled to 100-180℃ at a rate of 0.5-2℃ / min and kept for 60-180 minutes, and finally cooled with the furnace;

[0015] Step five: stabilization field application, a stabilization bias field with a field strength of 0.1-0.8 kV / mm and the same direction as the main polarization field is applied at room temperature, and the application time is 1-24 hours;

[0016] The interface modification layer is made of 40-60 parts of high dielectric constant ceramic powder, 10-20 parts of glass powder, 20-30 parts of organic silicone resin precursor, and 1-5 parts of coupling agent.

[0017] Preferably, in step one, the single crystal pretreatment includes the following steps:

[0018] The single crystal surface is finely polished to a surface roughness Ra≤5nm using diamond polishing liquid, then sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10-20 minutes, and then dried in a clean dry box at 60-80℃ for 1-2 hours.

[0019] Preferably, in step two, the application of the main polarization field uses a step-by-step voltage boosting method, specifically:

[0020] First, apply an initial field of 0.2-0.5 kV / mm for 5-10 minutes, then gradually increase to the target field strength at a rate of 0.1-0.3 kV / min;

[0021] The environment in the polarization device is silicon oil or inert gas atmosphere to prevent oxidation of the single crystal during high-temperature polarization.

[0022] Preferably, in the construction of the interface modification layer, the interface modification layer raw material is dispersed in an organic solvent to form a slurry with a solid content of 10-30wt%, the spin coating speed is 2000-5000rpm, the spin coating time is 30-60 seconds, and then preheating treatment is performed at 80-120℃ for 10-20 minutes to remove the solvent.

[0023] Preferably, in the interface modification layer raw material, the high dielectric constant ceramic powder is barium titanate, strontium titanate or lead-based perovskite ceramic powder.

[0024] The glass powder is borosilicate glass or phosphate glass, and the softening point temperature is 400-600℃.

[0025] The organic silicon resin precursor is methyl triethoxysilane or tetraethyl orthosilicate.

[0026] The coupling agent is γ-aminopropyl triethoxysilane or γ-glycidyl ether propyl trimethoxysilane.

[0027] Preferably, in the gradient annealing process in step four, the first stage of the temperature rising process is performed in a nitrogen protective atmosphere with an oxygen content of less than 50ppm to prevent the interface modification layer and the single crystal surface from deteriorating at high temperature.

[0028] Preferably, in the step five, the stabilizing bias electric field is applied in the form of a direct current electric field, or a quasi-direct current square wave electric field with a frequency of less than 1Hz, and the duty cycle of the square wave electric field is 50%-80%.

[0029] Preferably, after the step five, it further includes:

[0030] Step six: protective layer packaging, using epoxy resin or poly-p-xylylene to vacuum package the single crystal subjected to the stabilizing electric field treatment to form a protective layer with a thickness of 10-100 microns, and the packaging process is performed at room temperature to 60℃.

[0031] Preferably, the epoxy resin is bisphenol A type epoxy resin, the curing agent is anhydride or amine curing agent, and the mass ratio of the epoxy resin to the curing agent is 10:1 to 5:1.

[0032] The poly-p-xylylene is deposited by chemical vapor deposition, the deposition chamber pressure is 10-50Pa, and the deposition rate is 0.5-2μm / h.

[0033] Preferably, the trigonal phase relaxor ferroelectric single crystal is a lead magnesium niobate-lead titanate, lead zinc niobate-lead titanate or lead indium niobate-lead titanate system relaxor ferroelectric single crystal, and the deviation between the <001> oriented crystallographic direction and the direction of the main polarization electric field is less than 5°.

[0034] The physical principle of the single crystal pretreatment in the method is that:

[0035] The surface roughness is controlled at nanometer level by polishing, microcracks and defects are reduced, and local breakdown caused by electric field concentration is avoided; the chemical principle is that ultrasonic cleaning of acetone and ethanol can remove organic pollutants and ion residues, deionized water cleaning eliminates electrostatic adsorption, and the drying process prevents hydrolysis and oxidation, thereby ensuring the chemical inertness and electrical uniformity of the single crystal surface, providing an ideal interface for subsequent polarization.

[0036] The physical principle of the optimized polarization electric field is that the step-by-step boosting method gradually turns the electric domain by slowly increasing the electric field strength, avoiding domain wall pinning or breakdown caused by sudden electric field; the chemical principle is that the formation of an oxygen-deficient environment by silicone oil or inert gas atmosphere inhibits the oxidation reaction of the single crystal surface at high temperature, maintains the chemical stability of the crystal structure, and thus improves the polarization efficiency and durability.

[0042] The physical principle of the interface modification layer is that the high dielectric constant ceramic powder forms a continuous dielectric layer, reducing the accumulation of interface charges and electric field distortion, and enhancing the interface bonding strength; the chemical principle is that the glass powder softens and flows during annealing, filling the pores by sintering densification, and the organic silicone resin precursor forms a -Si-O- network through condensation reaction, and the coupling agent bridges the inorganic-organic interface through hydrolysis and condensation, improving the interlayer adhesion and chemical stability.

[0038] The chemical principle of the interface modification layer is that the B2O3 and SiO2 network in borosilicate glass forms a low-melting liquid phase during annealing, promoting interface diffusion bonding; the P-O-P chain of phosphate glass enhances hydrolysis resistance; the hydrolysis of the organic silicone resin precursor generates silanol, which forms a three-dimensional cross-linked structure through condensation, providing flexibility and thermal stability; the amino or epoxy groups of the coupling agent form covalent bonds with the hydroxyl groups on the single crystal surface, realizing molecular-level interface modification and inhibiting ion migration during depolarization.

[0039] The physical principle of using a direct current or quasi-direct current electric field to stabilize the polarization state is that the direct current provides a continuous polarization force, allowing the residual domain to be oriented and arranged, reducing the domain wall energy; the chemical principle is that the low-frequency alternating characteristic of the quasi-direct current square wave electric field promotes the pinning of the domain wall to the interface modification layer through periodic small perturbations, inhibiting depolarization caused by thermal activation; the duty cycle optimization ensures the proportion of the electric field action time, balancing the polarization efficiency and energy consumption.

[0040] Compared with the prior art, the present application provides a three-phase relaxation ferroelectric single crystal depolarization inhibition method based on interface modification, which has the following beneficial effects:

[0041] 1. In the present application, the single crystal is pretreated and the polarization electric field is optimized to ensure that the single crystal surface is smooth and clean, and a step-by-step boosting method is used to apply a main polarization electric field in a protective atmosphere, avoiding single crystal oxidation damage and improving polarization effect, laying a foundation for depolarization inhibition.

[0042] 2. In the present application, by interface modification layer construction and gradient annealing treatment, a high dielectric constant interface layer is formed on the surface of single crystal, and internal stress is eliminated in a protective atmosphere through a multi-stage program temperature control annealing, the interface bonding strength and crystal structure stability are enhanced, and the depolarization process is inhibited.

[0043] 3. In the present application, by stabilizing the bias electric field and packaging the protective layer, the polarization state is further stabilized by using direct current or quasi-direct current electric field, and the protective layer is formed by vacuum packaging to prevent performance degradation caused by environmental factors, and long-term depolarization inhibition is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The present application is a three-phase relaxation ferroelectric single crystal depolarization suppression method based on interface modification. The effect of the method realized in the second embodiment of the present application is compared with the existing three-phase relaxation ferroelectric single crystal depolarization suppression method.

[0045] Figure 2 The flowchart of the present application is a three-phase relaxation ferroelectric single crystal depolarization suppression method based on interface modification. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0047] Embodiment one: please refer to Figure 2 : A three-phase relaxation ferroelectric single crystal depolarization suppression method based on interface modification, comprising the following steps:

[0048] Step one: single crystal pretreatment, select three-phase relaxation ferroelectric single crystal, polish, clean and dry the surface;

[0049] Step two: polarization field optimization, place the pretreated single crystal in a controllable temperature polarization device, apply a main polarization electric field with a field strength of 0.5 kV / mm along its spontaneous polarization direction, the polarization temperature is 80℃, and the polarization time is 10 minutes;

[0050] Step three: interface modification layer construction, prepare a 10 nanometer thick interface modification layer on the surface of the polarized single crystal;

[0051] Step four: gradient annealing treatment, place the single crystal in a program temperature control furnace for multi-stage gradient annealing, first heat to 200℃ at 1℃ / min and keep for 30 minutes, then cool to 100℃ at 0.5℃ / min and keep for 60 minutes, and finally cool with the furnace;

[0052] Step five: applying a stabilizing electric field, applying a stabilizing bias electric field with a field strength of 0.1 kV / mm and a direction consistent with the main polarization electric field at room temperature for 1 hour;

[0053] The interface modification layer is made of 40 parts of barium titanate powder as high dielectric constant ceramic powder, 10 parts of borosilicate glass powder as glass powder, 20 parts of methyl triethoxysilane as organic silicon resin precursor, and 1 part of γ-aminopropyl triethoxysilane as coupling agent.

[0054] In step one, the single crystal pretreatment includes the following steps:

[0055] The surface of the single crystal is finely polished to a surface roughness Ra≤5 nm by using a diamond polishing liquid, and then ultrasonic cleaning is performed in acetone, ethanol and deionized water for 10 minutes each. After cleaning, it is placed in a clean dry box and dried at 60°C for 1 hour.

[0056] In step two, the main polarization electric field is applied by using a step-by-step voltage increasing method, specifically:

[0057] First, an initial electric field of 0.2 kV / mm is applied for 5 minutes, and then gradually increased to the target field strength at a rate of 0.1 kV / min;

[0058] The environment in the polarization device is silicon oil or inert gas atmosphere to prevent oxidation of the single crystal during high-temperature polarization.

[0059] In the construction of the interface modification layer, the interface modification layer raw materials are dispersed in an organic solvent to form a slurry with a solid content of 10wt%, the spin coating speed is 2000 rpm, the spin coating time is 30 seconds, and then the solvent is removed by preheating at 80°C for 10 minutes.

[0060] In the interface modification layer raw materials, the glass powder is borosilicate glass or phosphate glass, and the softening point temperature is 400°C;

[0061] The organic silicon resin precursor is methyl triethoxysilane or tetraethyl orthosilicate;

[0062] The coupling agent is γ-aminopropyl triethoxysilane or γ-glycidyl ether propyl trimethoxysilane.

[0063] The first stage of the gradient annealing process in step four is carried out in a nitrogen atmosphere with an oxygen content of less than 50 ppm to prevent degradation of the interface modification layer and the single crystal surface at high temperatures.

[0064] The stabilizing bias electric field in step five is a direct current electric field or a quasi-direct current square wave electric field with a frequency of less than 1 Hz, and the duty cycle of the square wave electric field is 50%.

[0065] After step five, it also includes:

[0066] Step six: protective layer encapsulation, vacuum encapsulation of the single crystal after the electric field stabilization treatment is performed using an epoxy resin or parylene to form a protective layer with a thickness of 10 microns, and the encapsulation process is performed at room temperature to 60°C.

[0067] The epoxy resin is a bisphenol A type epoxy resin, and the curing agent is an acid anhydride or an amine curing agent, and the mass ratio of the epoxy resin to the curing agent is 10:1;

[0068] The parylene is deposited by chemical vapor deposition, and the deposition chamber pressure is 10 Pa, and the deposition rate is 0.5 μm / h.

[0069] The trigonal phase relaxor ferroelectric single crystal is a lead magnesium niobate-lead titanate, lead zinc niobate-lead titanate or lead indium niobate-lead titanate system relaxor ferroelectric single crystal, and the deviation between the crystallographic direction of the <001> orientation and the direction of the main polarization electric field is less than 5°.

[0070] Example two: please refer to Figure 1 and Figure 2 : a method for inhibiting depolarization of a trigonal phase relaxor ferroelectric single crystal based on interface modification, comprising the following steps:

[0071] Step one: single crystal pretreatment, select a trigonal phase relaxor ferroelectric single crystal, polish, clean and dry the surface;

[0072] Step two: polarization electric field optimization, place the pretreated single crystal in a controllable temperature polarization device, and apply a main polarization electric field with a field strength of 1.7 kV / mm along its spontaneous polarization direction, the polarization temperature is 115°C, and the polarization time is 35 minutes;

[0073] Step three: interface modification layer construction, a layer of interface modification layer with a thickness of 445 nanometers is prepared on the surface of the polarized single crystal;

[0074] Step four: gradient annealing treatment, place the single crystal in a program-controlled temperature furnace for multi-stage gradient annealing, first heat to 250°C at 3°C / min and keep for 60 minutes, then cool to 140°C at 1.2°C / min and keep for 120 minutes, and finally cool with the furnace;

[0075] Step five: stabilization electric field application, apply a stabilization bias electric field with a field strength of 0.4 kV / mm and the same direction as the main polarization electric field at room temperature, and the application time is 12 hours;

[0076] The interface modification layer is made of 50 parts of barium titanate powder as high dielectric constant ceramic powder, 15 parts of phosphate glass powder as glass powder, 25 parts of tetraethyl orthosilicate as organic silicon resin precursor, and 3 parts of γ-glycidoxypropyltrimethoxysilane as coupling agent.

[0077] In step one, the single crystal pretreatment includes the following steps:

[0078] The surface of the single crystal is finely polished to a surface roughness Ra≤5nm using a diamond polishing liquid, and then sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 15 minutes each. After cleaning, it is placed in a clean dry box and dried at 70°C for 1.5 hours.

[0079] In step two, the application of the main polarization electric field uses a step-by-step boosting method, specifically:

[0080] An initial electric field of 1.1 kV / mm is first applied and maintained for 7 minutes, and then gradually increased to the target field strength at a rate of 0.2 kV / min;

[0081] The environment in the polarization device is a silicone oil or inert gas atmosphere to prevent oxidation of the single crystal during high-temperature polarization.

[0082] In the construction of the interface modification layer, when using physical vapor deposition, the process parameters are: sputtering power 200 W, working pressure 1.2 Pa, substrate temperature 150°C, and deposition rate 0.3 nm / s;

[0083] When using spin coating, the interface modification layer raw material is first dispersed in an organic solvent to form a slurry with a solid content of 20wt%, the spin coating speed is 3500 rpm, the spin coating time is 45 seconds, and then preheated at 100°C for 15 minutes to remove the solvent.

[0084] In the interface modification layer raw material, the glass powder is borosilicate glass or phosphate glass, and the softening point temperature is 500°C;

[0085] The organosilicon resin precursor is methyl triethoxysilane or tetraethyl orthosilicate;

[0086] The coupling agent is γ-aminopropyl triethoxysilane or γ-glycidyl ether propyl trimethoxysilane.

[0087] In step four, the first stage of the gradient annealing process is carried out in a nitrogen atmosphere with an oxygen content of less than 50 ppm to prevent degradation of the interface modification layer and the single crystal surface at high temperatures.

[0088] In step five, the stabilizing bias electric field is applied as a direct current electric field, or as a quasi-direct current square wave electric field with a frequency of less than 1 Hz, and the duty cycle of the square wave electric field is 65%.

[0089] After step five, it also includes:

[0090] Step six: protective layer packaging, using epoxy resin or poly-p-xylene to vacuum package the single crystal after stabilizing electric field treatment, forming a protective layer with a thickness of 55 microns, and the packaging process is carried out at room temperature to 60°C.

[0091] The epoxy resin is bisphenol A type epoxy resin, and the curing agent is anhydride or amine curing agent, and the mass ratio of the epoxy resin to the curing agent is 5:1;

[0092] The parylene is deposited by chemical vapor deposition method, and the deposition chamber pressure is 30 Pa, and the deposition rate is 1.2 μm / h.

[0093] The trigonal phase relaxor ferroelectric single crystal is a lead magnesium niobate-lead titanate, lead zinc niobate-lead titanate or lead indium niobate-lead titanate system relaxor ferroelectric single crystal, and the deviation between the crystallographic direction of the <001> orientation and the direction of the main polarization electric field is less than 5°.

[0094] Example three: please refer to Figure 2 A method for inhibiting depolarization of a trigonal phase relaxor ferroelectric single crystal based on interface modification, comprising the following steps:

[0095] Step one: single crystal pretreatment, selecting a trigonal phase relaxor ferroelectric single crystal, polishing, cleaning and drying the surface;

[0096] Step two: polarization field optimization, placing the pretreated single crystal in a controllable temperature polarization device, applying a main polarization electric field with a field strength of 3.0 kV / mm along its spontaneous polarization direction, the polarization temperature is 150℃, and the polarization time is 60 minutes;

[0097] Step three: interface modification layer construction, preparing an interface modification layer with a thickness of 500 nanometers on the surface of the polarized single crystal;

[0098] Step four: gradient annealing treatment, placing the single crystal in a program-controlled temperature furnace for multi-stage gradient annealing, first heating to 300℃ at 5℃ / min and keeping for 90 minutes, then cooling to 180℃ at 2℃ / min and keeping for 180 minutes, and finally cooling with the furnace;

[0099] Step five: stable electric field application, applying a stable bias electric field with a field strength of 0.8 kV / mm and a direction consistent with the main polarization electric field at room temperature, and the application time is 24 hours;

[0100] The interface modification layer is made of 60 parts of lead zirconate titanate powder as high dielectric constant ceramic powder, 20 parts of borosilicate glass powder as glass powder, 30 parts of methyl triethoxysilane as organosilicon resin precursor, and 5 parts of γ-aminopropyl triethoxysilane as coupling agent.

[0101] In step one, the single crystal pretreatment includes the following steps:

[0102] The single crystal surface is finely polished by diamond polishing liquid to a surface roughness Ra≤5nm, and then sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 20 minutes, and dried at 80℃ for 2 hours in a clean dry box after cleaning.

[0103] In step two, the application of the main polarization electric field adopts a step-by-step boosting method, specifically:

[0104] An initial electric field of 0.5kV / mm is first applied and maintained for 10 minutes, and then gradually increased to the target field strength at a rate of 0.3kV / min;

[0105] The environment in the polarization device is a silicone oil or inert gas atmosphere to prevent oxidation of the single crystal during high-temperature polarization.

[0106] In the construction of the interface modification layer, when using physical vapor deposition, the process parameters are: sputtering power 300W, working pressure 2.0Pa, substrate temperature 200℃, deposition rate 0.5nm / s;

[0107] When using spin coating, the interface modification layer raw material is first dispersed in an organic solvent to form a slurry with a solid content of 30wt%, the spin coating speed is 5000rpm, the spin coating time is 60 seconds, and then preheated at 120℃ for 20 minutes to remove the solvent.

[0108] In the interface modification layer raw material, the glass powder is borosilicate glass or phosphate glass, and the softening point temperature is 600℃;

[0109] The organosilicon resin precursor is methyl triethoxysilane or tetraethyl orthosilicate;

[0110] The coupling agent is γ-aminopropyl triethoxysilane or γ-glycidyl ether propyl trimethoxysilane.

[0111] In the gradient annealing process in step four, the first stage of the heating process is carried out in a nitrogen protective atmosphere with an oxygen content of less than 50ppm to prevent the interface modification layer and the single crystal surface from deteriorating at high temperatures.

[0112] The stabilizing bias electric field in step five is applied as a direct current electric field, or as a quasi-direct current square wave electric field with a frequency of less than 1Hz, and the duty cycle of the square wave electric field is 80%.

[0113] After step five, it also includes:

[0114] Step six: protective layer packaging, using epoxy resin or poly-p-xylene to vacuum package the single crystal after stabilizing electric field treatment, forming a protective layer with a thickness of 100 microns, and the packaging process is carried out at room temperature to 60℃.

[0115] The epoxy resin is bisphenol A type epoxy resin, and the curing agent is anhydride or amine curing agent, and the mass ratio of the epoxy resin to the curing agent is 5:1.

[0116] The parylene is deposited by chemical vapor deposition method, and the deposition chamber pressure is 50 Pa, and the deposition rate is 2 μm / h.

[0117] The trigonal phase relaxor ferroelectric single crystal is a lead magnesium niobate-lead titanate, lead zinc niobate-lead titanate or lead indium niobate-lead titanate system relaxor ferroelectric single crystal, and the deviation between the crystallographic direction of the <001> orientation and the direction of the main polarization electric field is less than 5°.

[0118] Comparative Example 1, the difference between the comparative example and example one is that the comparative example does not construct an interface modification layer.

[0119] Comparative Example 2, the difference between the comparative example and example one is that the comparative example does not perform gradient annealing treatment.

[0120] Comparative Example 3, the difference between the comparative example and example one is that the comparative example does not apply a stabilizing bias electric field.

[0121] Comparative Example 4, the difference between the comparative example and example one is that the comparative example does not perform protective layer packaging.

[0122] The trigonal phase relaxor ferroelectric single crystals prepared in examples one to three and comparative examples 1 to 4 are tested for performance, and the test items and test methods are as follows:

[0123] Piezoelectric constant d33 test, at room temperature 25℃, frequency 100Hz, using quasi-static d33 measuring instrument, applying pressure 0.25N, measuring piezoelectric strain coefficient;

[0124] Dielectric loss test, at a frequency of 1 kHz and a voltage of 1 Vrms, using an impedance analyzer to measure the dielectric constant and loss tangent;

[0125] Depolarization rate test, aging at high temperature 150℃ for 100 hours, then cooling to room temperature, measuring the attenuation percentage of piezoelectric constant d33;

[0126] Bending strength test, using a universal material testing machine for testing.

[0127] The test data of the trigonal phase relaxor ferroelectric single crystals prepared in examples one to three and comparative examples 1 to 4 are recorded in the following table:

[0128]

[0129] By comparing and analyzing the data in the table, it can be seen that the three-phase relaxor ferroelectric single crystals prepared by the methods in Examples 1-3 have more excellent performance than the single crystals prepared by the methods in Comparative Examples 1-4, which shows that the present application ensures the smooth and clean surface of the single crystal by single crystal pretreatment and optimization of the polarization electric field, avoids the oxidation damage of the single crystal and improves the polarization effect by applying the main polarization electric field in a protective atmosphere through the step-by-step boosting method, lays a foundation for the inhibition of depolarization, forms a high dielectric constant interface layer on the surface of the single crystal through interface modification layer construction and gradient annealing treatment, eliminates internal stress in a protective atmosphere through multi-stage program temperature annealing, enhances the interface bonding strength and crystal structure stability, and inhibits the depolarization process, and through the application of a stable bias electric field and the encapsulation of a protective layer, the polarization state is further stabilized by a direct current or quasi-direct current electric field, and a protective layer is formed through vacuum encapsulation to prevent performance degradation caused by environmental factors, thereby achieving the inhibition of depolarization.

[0130] By comparing and analyzing the relevant data in the table, it can be seen that the three-phase relaxor ferroelectric single crystals prepared by the method of the present application have high piezoelectric constant, low dielectric loss, low depolarization rate and good mechanical strength.

[0131] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without limitation, an element preceded by "comprises... a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0132] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for suppressing depolarization in trigonal phase relaxor ferroelectric single crystals based on interface modification, characterized in that: The method comprises the following steps: Step one: single crystal pretreatment, select rhombohedral phase relaxor ferroelectric single crystal, surface polishing, cleaning and drying; Step two: polarization field optimization, the pretreated single crystal is placed in a controllable temperature polarization device, a main polarization electric field with a field strength of 0.5-3.0 kV / mm is applied along the spontaneous polarization direction, the polarization temperature is 80-150℃, and the polarization time is 10-60 minutes; Step three: interface modification layer construction, a 10-500 nm thick interface modification layer is prepared on the surface of the polarized single crystal; Step four: gradient annealing treatment, the single crystal is placed in a program-controlled temperature furnace for multi-stage gradient annealing, first heated to 200-300℃ at a rate of 1-5℃ / min and kept for 30-90 minutes, then cooled to 100-180℃ at a rate of 0.5-2℃ / min and kept for 60-180 minutes, and finally cooled with the furnace; Step five: application of a stabilizing electric field, a stabilizing bias electric field with a field strength of 0.1-0.8 kV / mm and the same direction as the main polarization electric field is applied at room temperature, and the application time is 1-24 hours. The interface modification layer is made of 40-60 parts of high dielectric constant ceramic powder, 10-20 parts of glass powder, 20-30 parts of organic silicon resin precursor, and 1-5 parts of coupling agent; the high dielectric constant ceramic powder is barium titanate, strontium titanate, or lead-based perovskite ceramic powder.

2. The method of depolarization suppression of a ternary phase relaxor ferroelectric single crystal based on interface modification according to claim 1, characterized in that: In step one, the single crystal pretreatment comprises the following steps: The single crystal surface is finely polished to a surface roughness Ra≤5 nm using a diamond polishing liquid, then sequentially ultrasonically cleaned in acetone, ethanol, and deionized water for 10-20 minutes, and then dried in a clean dry box at 60-80℃ for 1-2 hours.

3. The method of claim 1, wherein the interface-modified ternary relaxor ferroelectric single crystal is represented by the formula: (1-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3. In step two, the application of the main polarization electric field uses a step-by-step voltage boosting method, specifically: First, apply an initial electric field of 0.2-0.5 kV / mm for 5-10 minutes, then gradually increase to the target field strength at a rate of 0.1-0.3 kV / min; The environment in the polarization device is silicon oil or inert gas atmosphere to prevent oxidation of the single crystal during high-temperature polarization.

4. The method for suppressing depolarization of trigonal phase relaxor ferroelectric single crystals based on interface modification according to claim 1, characterized in that: In the construction of the interface modification layer, the interface modification layer raw materials are dispersed in an organic solvent to form a slurry with a solid content of 10-30 wt%, the spin coating speed is 2000-5000 rpm, the spin coating time is 30-60 seconds, and then preheated at 80-120℃ for 10-20 minutes to remove the solvent.

5. The method for suppressing depolarization of trigonal phase relaxor ferroelectric single crystals based on interface modification according to claim 1, characterized in that: In the interface modification layer raw materials, The glass powder is borosilicate glass or phosphate glass with a softening point temperature of 400-600℃; The organic silicon resin precursor is methyl triethoxysilane or tetraethyl orthosilicate; The coupling agent is γ-aminopropyl triethoxysilane or γ-glycidyl ether propyl trimethoxysilane.

6. The method of suppressing depoling in an interface-modified ternary phase relaxor ferroelectric single crystal according to claim 1, wherein: In the gradient annealing treatment of step four, the first stage of the heating process is carried out in a nitrogen atmosphere with an oxygen content of less than 50 ppm to prevent degradation of the interface modification layer and the single crystal surface at high temperatures.

7. The method of suppressing depoling in an interface-modified ternary phase relaxor ferroelectric single crystal according to claim 1, wherein: The stabilizing bias electric field in the fifth step is a direct current electric field or a quasi-direct current square wave electric field with a frequency lower than 1 Hz and a duty cycle of 50%-80%.

8. The method of suppressing depoling in an interface-modified ternary phase relaxor ferroelectric single crystal according to claim 1, wherein: After the fifth step, the method further comprises: A sixth step of encapsulating the single crystal subjected to the stabilizing electric field treatment with an epoxy resin or a parylene to form a protective layer with a thickness of 10-100 microns, wherein the encapsulating process is performed at room temperature to 60°C.

9. A method for suppressing depolarization of trigonal phase relaxor ferroelectric single crystals based on interface modification according to claim 8, characterized in that: The epoxy resin is a bisphenol A type epoxy resin, and the curing agent is an acid anhydride or an amine curing agent, and the mass ratio of the epoxy resin to the curing agent is 10:1 to 5:

1. The parylene is deposited by a chemical vapor deposition method, and the pressure in the deposition chamber is 10-50 Pa, and the deposition rate is 0.5-2 microns / hour.

10. The method of suppressing depoling in an interface-modified ternary phase relaxor ferroelectric single crystal according to claim 1, wherein: The trigonal phase relaxor ferroelectric single crystal is a lead magnesium niobate-lead titanate, lead zinc niobate-lead titanate or lead indium niobate-lead titanate relaxor ferroelectric single crystal, and the deviation between the crystallographic direction of the <001> orientation and the direction of the main polarization electric field is less than 5°.

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