Hard piezoelectric ceramic based on high orientation degree precipitated phase and preparation method thereof

Abstract

The application discloses a kind of hard piezoelectric ceramics based on high orientation degree precipitated phase and its preparation method, the method of the present application is based on traditional aging mode, before aging, piezoelectric ceramic is applied to sample uniaxial mechanical stress, then the sample is heated to precipitated phase nucleation temperature under the state of applied axial force, and is kept for a proper time, so that the precipitated phase nucleus has high number density;Again, the sample is heated to precipitated phase growth temperature, and is kept for a proper time, so that the precipitated phase with high orientation degree grows fully, and the size reaches hundreds of nanometers order of magnitude;Finally, the sample is cut along the direction of applied axial force, and the direction of external excitation is adjusted so that the current precipitated phase orientation is the orientation with optimal obstacle ability to domain wall.The present application can effectively realize the substantial promotion of precipitated phase orientation degree, so that the precipitated phase is precipitated along the orientation with strong obstacle ability to domain wall, thereby substantially promoting the effect of precipitated phase piezoelectric hardening.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of piezoelectric ceramic materials, and particularly relates to a hard piezoelectric ceramic based on a high-orientation degree precipitated phase and a preparation method thereof. BACKGROUND

[0002] The piezoelectric material often accompanies severe mechanical loss when working near the resonance frequency, which leads to a significant reduction in vibration amplitude. Therefore, the piezoelectric material used for resonance application usually needs to be subjected to piezoelectric hardening treatment, that is, a certain treatment method is used to reduce the mechanical loss. The ferroelectric type piezoelectric ceramic is the most widely used piezoelectric material at present. The domain wall movement under external field excitation is the main source of mechanical loss in this type of material. The traditional piezoelectric ceramic hardening method is a main doping hardening method. This method can introduce charged defects, oxygen vacancies, and the oxygen vacancies can move directionally to form an internal electric field after a period of time. The internal electric field can stabilize the electric domain structure, thereby hindering the domain wall movement of the piezoelectric material under external excitation. However, due to the high mobility of point defects, the internal electric field formed by the point defects is unstable, and the hardening effect is greatly reduced under high temperature or high power application. Recently, a new type of piezoelectric hardening method based on precipitated phase has been proposed. This method can introduce a sheet-shaped precipitated phase with high aspect ratio and high temperature stability, and use the precipitated phase to effectively hinder the domain wall movement, thereby realizing piezoelectric hardening. However, the precipitated phase introduced by the traditional aging method has multiple orientations and the occurrence probability of each orientation is equal. The precipitated phase with weak hindering ability to the domain wall will reduce the overall hardening effect of the material. Therefore, the preferred orientation of the precipitated phase is the key to improving the performance of the precipitated phase piezoelectric hardening method. SUMMARY

[0003] The application aims to overcome the problem of random orientation of the precipitated phase in the prior art, and provides a hard piezoelectric ceramic based on a high-orientation degree precipitated phase and a preparation method thereof. The application is a new type of precipitated phase introduction method, which can effectively realize a significant increase in the orientation degree of the precipitated phase, so that the precipitated phase is precipitated along the orientation with strong hindering ability to the domain wall, thereby greatly improving the effect of the precipitated phase piezoelectric hardening.

[0004] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0005] A preparation method of a hard piezoelectric ceramic based on a high-orientation degree precipitated phase, comprising the following processes:

[0006] An axial force is applied to a sample of a piezoelectric ceramic solid solution system with supersaturated solute;

[0007] The sample is subjected to aging treatment in the state of applying the axial force;

[0008] The sample after the aging treatment is cut to obtain the hard piezoelectric ceramic based on the high-orientation precipitated phase.

[0009] Preferably, when the sample of the piezoelectric ceramic solid solution system with the supersaturated solute is subjected to the axial force, the axial force applied is 40% to 80% of the compressive strength of the material of the sample.

[0010] Preferably, the process of the aging treatment of the sample under the axial force includes:

[0011] The sample is heated to the nucleation temperature of the precipitated phase and is kept at the temperature, so that the nucleation density of the precipitated phase is increased.

[0012] Then, the sample is continuously heated to the growth temperature of the precipitated phase and is kept at the temperature, so that the precipitated phase is fully grown, and the aging treatment is ended.

[0013] Preferably, in the process of continuously heating the sample to the growth temperature of the precipitated phase and keeping the sample at the temperature, the size of the precipitated phase reaches the order of magnitude of several hundred nanometers.

[0014] Preferably, when the sample after the aging treatment is cut, the cutting direction is parallel to the direction of the axial force applied.

[0015] Preferably, the preparation method of the present application further includes the following process:

[0016] After the sample after the aging treatment is cut, electrodes are prepared on the cutting plane.

[0017] Preferably, the electrodes are plated on the cutting plane by plasma sputtering.

[0018] Preferably, the sample of the piezoelectric ceramic solid solution system with the supersaturated solute is the LNN piezoelectric ceramic.

[0019] Preferably, the chemical formula of the LNN piezoelectric ceramic is Li 0.18 Na 0.82 NbO3.

[0020] The present application also provides a hard piezoelectric ceramic based on a high-orientation precipitated phase, which is prepared by the preparation method of the present application.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The preparation method of the present application is based on the traditional aging method, an axial force is applied to the sample before aging treatment, and then the sample is subjected to aging treatment in the state of applying the axial force, so that the high orientation consistency of precipitated phase in the piezoelectric ceramic matrix can be realized. The Rayleigh test shows that, compared with the traditional precipitated phase hardening method, the nonlinear coefficient ratio a / e0 (indicating the relative contribution degree of domain wall motion) of the piezoelectric ceramic obtained by using the preparation method of the present application is greatly reduced, indicating that the preparation method of the present application has obvious enhancement on the suppression of domain wall motion under small signal excitation (external electric field less than 1 / 4 times the coercive electric field). Through experiments, compared with the traditional precipitated phase hardening method, the residual polarization intensity P r of the piezoelectric ceramic prepared by using the preparation method of the present application is greatly reduced after 8kV / mm electric field polarization at room temperature, and the polarization intensity under 8kV / mm electric field is less than the increase amplitude of the traditional precipitated phase hardening method at 120℃, indicating that the preparation method of the present application has obvious enhancement on the suppression of domain wall motion under large signal excitation and temperature stability. In addition, it can be seen from the preparation method of the present application that the preparation method of the present application is simple and easy to control, can be applied to actual production, and has certain economic and social effects. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1(a) is a schematic diagram of a piezoelectric ceramic preparation device with high orientation degree precipitated phase adopted in the embodiment of the present application;

[0024] Fig. 1(b) is a schematic diagram of a piezoelectric ceramic preparation process with high orientation degree precipitated phase adopted in the embodiment of the present application;

[0025] Figure 2 Fig. 2 is a high vibration speed stability comparison diagram of precipitated phase hardened piezoelectric ceramic, commercial PZT piezoelectric ceramic and traditional acceptor doped hardened KNN piezoelectric ceramic in the embodiment of the present application; m

[0026] Fig. 3(a) is a Rayleigh test result diagram of a traditional aging sample and a high orientation degree precipitated phase sample in the embodiment of the present application;

[0027] Fig. 3(b) is a nonlinear coefficient ratio diagram of a traditional aging sample and a high orientation degree precipitated phase sample in the embodiment of the present application;

[0028] Fig. 4(a) is a hysteresis loop comparison diagram of a traditional aging sample and a high orientation degree precipitated phase sample in the embodiment of the present application;

[0029] Fig. 4(b) is a residual polarization intensity comparison diagram of a traditional aging sample and a high orientation degree precipitated phase sample in the embodiment of the present application;

[0030] Figure 5 Fig. 5 is a polarization intensity temperature stability comparison diagram of a traditional aging sample and a high orientation degree precipitated phase sample in the embodiment of the present application. ​

[0031] In the figure, 1 - through hole, 2 - furnace wall, 3 - high temperature resistance furnace, 4 - aluminum oxide accessory, 5 - sample. DETAILED DESCRIPTION

[0032] The application will be further described in detail below in combination with the drawings and examples:

[0033] The preparation method of the hard piezoelectric ceramic with high orientation degree precipitated phase mainly includes the following steps:

[0034] First, a sample of piezoelectric ceramic solid solution system with supersaturated solute is prepared; then, based on the traditional aging method, a uniaxial mechanical stress is applied to the sample by using the device shown in Fig. 1(a) before aging, and then the sample is heated to the nucleation temperature of the precipitated phase and kept for an appropriate time, so that the precipitated phase nucleus has a high number density; then the sample is heated to the growth temperature of the precipitated phase and kept for an appropriate time, so that the precipitated phase with high orientation degree grows fully and the size reaches the order of hundreds of nanometers; finally, the sample is cut along the direction of the applied axial force, and the external excitation direction is adjusted so that the current precipitated phase orientation is the orientation with the optimal hindering ability to the domain wall.

[0035] Example 1

[0036] The sample of piezoelectric ceramic solid solution system with supersaturated solute used in this example is a hard lithium sodium niobate (LNN) piezoelectric ceramic sample with high orientation degree precipitated phase, and the preparation method of the hard piezoelectric ceramic with high orientation degree precipitated phase in this example includes the following steps:

[0037] Step (1): LNN piezoelectric ceramic is prepared by solid phase reaction method, raw materials are mixed according to the chemical composition ratio of Li 0.18 Na 0.82 NbO3, the ceramic raw material powder is dry pressed into a mold with a diameter of 6.5 mm at a temperature of 850 ℃ for 4 h, the green compact size is Φ6.5 mm × 12 mm, and then the green compact is sintered at 1300 ℃ for 3 h and cooled to room temperature by air quenching to obtain the LNN piezoelectric ceramic sample;

[0038] Step (2): Referring to Fig. 1(a), a uniaxial mechanical stress of 150 MPa is applied to the LNN piezoelectric ceramic sample, and the piezoelectric ceramic is aged and heat treated while the stress is maintained, as shown in Fig. 1(b). The aging and heat treatment process in this example includes: keeping at 550 ℃ for 24 h, then heating to 650 ℃ and keeping for 8 h, so that the precipitated phase particles with high orientation are introduced into the LNN ceramic sample;

[0039] Step (3): Cut the LNN piezoelectric ceramic sample treated by the above method. The cutting direction is parallel to the direction of the applied mechanical stress. Plasma sputtering is used to deposit electrodes on the cutting plane so that the direction of the external excitation electric field is perpendicular to the direction of the mechanical stress.

[0040] like Figure 2 As shown, the LNN piezoelectric ceramic sample prepared in this embodiment exhibits a high mechanical quality factor Q at a vibration speed as high as 0.8 m / s. m It can still maintain Q under small signal excitation m The 90% result indicates that the piezoelectric hardening effect of this embodiment has good stability under high-power drive.

[0041] As shown in Figure 3(a), the LNN piezoelectric ceramic sample prepared in this embodiment exhibits a high degree of orientation consistency of the precipitated phase in the piezoelectric ceramic matrix, and by adjusting the electrode plane, the resistance of the precipitated phase to the domain walls is significantly enhanced.

[0042] As shown in Figure 3(b), Rayleigh spectroscopy results indicate that, compared to the traditional precipitate hardening method, the nonlinear coefficient ratio a / e0 (indicating the relative contribution of domain wall motion) of the LNN piezoelectric ceramic sample prepared in this embodiment is higher than that prepared by this technique, which is 1.65E. -4 Decreased to 1.08E -4 (The reduction was 35%), indicating that the method significantly enhances the suppression of domain wall motion under small signal excitation.

[0043] As shown in Figure 4(a), Figure 4(b) and Figure 5 As shown, compared to the traditional precipitation phase hardening method, the piezoelectric ceramic prepared by the method of this invention exhibits a higher remanent polarization intensity P after polarization at room temperature and in an electric field of 8 kV / mm. r From 1.3mC / cm 2 Reduced to 0.6 mC / cm 2 (The reduction was 54%), and the polarization intensity under an 8kV / mm electric field increased by 15% at 120℃ (compared to 25.8% for the traditional precipitate hardening method), indicating that this method significantly enhances the suppression of domain wall motion and temperature stability under large signal excitation.

Claims

1. A method for producing a hard piezoelectric ceramic based on a high-orientation precipitate phase, characterized by, The process comprises the following steps: applying axial force to a sample of a piezoelectric ceramic solid solution system with supersaturated solute; the sample of the piezoelectric ceramic solid solution system with supersaturated solute is LNN piezoelectric ceramic; aging the sample under the applied axial force; cutting the sample after the aging to obtain the hard piezoelectric ceramic based on high orientation degree precipitated phase; when applying axial force to the sample of the piezoelectric ceramic solid solution system with supersaturated solute, the axial force applied is 40% to 80% of the compressive strength of the sample material; the process of aging the sample under the applied axial force comprises the following steps: warming the sample to the nucleation temperature of the precipitated phase and keeping the temperature, so that the number density of the nucleated precipitated phase is increased; then, continuously warming the sample to the growth temperature of the precipitated phase and keeping the temperature, so that the precipitated phase is fully grown and the aging is ended.

2. The method for producing a hard piezoelectric ceramic based on a high-orientation precipitate phase according to claim 1, characterized by, In the process of continuously warming the sample to the growth temperature of the precipitated phase and keeping the temperature, the size of the precipitated phase reaches the order of several hundred nanometers.

3. The method for preparing a hard piezoelectric ceramic based on a highly oriented precipitated phase according to claim 1, characterized in that, When cutting the sample after the aging, the cutting direction is parallel to the direction of the applied axial force.

4. The method for preparing a hard piezoelectric ceramic based on a highly oriented precipitated phase according to claim 1, characterized in that, The process further comprises the following steps: after cutting the sample after the aging, preparing electrodes on the cutting plane.

5. The method for preparing a hard piezoelectric ceramic based on a highly oriented precipitated phase according to claim 4, characterized in that, plating electrodes on the cutting plane by plasma sputtering.

6. The method for preparing a hard piezoelectric ceramic based on a highly oriented precipitated phase according to claim 1, characterized in that, The chemical formula of the LNN piezoelectric ceramic is Li 0.18 Na 0.82 NbO3.

7. A hard piezoelectric ceramic based on a high degree of orientation of precipitates, characterized in that, The hard piezoelectric ceramic based on high orientation degree precipitated phase is prepared by any one of the preparation methods of claims 1-6.

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