Method for obtaining large pseudo plastic deformation of ferroelectric material
阅读说明：本技术 一种使铁电材料获得大伪塑性变形的方法 (Method for obtaining large pseudo plastic deformation of ferroelectric material ) 是由 初宝进 陈攀 于 2020-12-09 设计创作，主要内容包括：本发明提供了一种使铁电材料获得大伪塑性变形的方法,包括：在应力作用下,将铁电材料进行先升温再降温的热处理,所述先升温再降温的热处理的峰值温度高于所述铁电材料的低对称性相到高对称性相的相变温度。本发明提出了一种铁电材料在施加外力下实现大的可恢复的类塑性变形的方法,可操作性强、工艺较为简单,小应力的作用可有效降低陶瓷破裂的风险；产生的伪塑性变形量可完全恢复,可重复利用率较高；填补了小应力应用场合的材料选择；丰富了高温、腐蚀等极端条件下应力缓冲器、驱动器应用结构陶瓷的选择范围,尤其是小应力范围应用的情况。(The invention provides a method for obtaining large pseudo plastic deformation of a ferroelectric material, which comprises the following steps: under the action of stress, the ferroelectric material is subjected to heat treatment of firstly heating and then cooling, and the peak temperature of the heat treatment of firstly heating and then cooling is higher than the phase transition temperature from the low symmetry phase to the high symmetry phase of the ferroelectric material. The invention provides a method for realizing large recoverable plastic-like deformation of a ferroelectric material under the action of an applied external force, which has strong operability and simpler process, and can effectively reduce the risk of ceramic fracture under the action of small stress; the generated pseudo plastic deformation can be completely recovered, and the repeatable utilization rate is high; the material selection of small stress application occasions is filled; the selection range of the stress buffer and the driver applying structural ceramics under extreme conditions of high temperature, corrosion and the like is enriched, and particularly the application condition of a small stress range is enriched.)
1. A method of obtaining a pseudo-plastic deformation of a ferroelectric material, comprising:
under the action of stress, the ferroelectric material is subjected to heat treatment of firstly heating and then cooling, the peak temperature of the heat treatment of firstly heating and then cooling is higher than the phase transition temperature from the low symmetry phase to the high symmetry phase of the ferroelectric material or the phase transition temperature from the ferroelectric phase to the paraelectric phase, and the ferroelectric material obtains pseudo plastic deformation.
2. The method of claim 1, wherein the stress is < 1 GPa.
3. The method of claim 1, wherein the stress is such that the ferroelectric material is strained by < 15%.
4. The method of claim 1, wherein the ferroelectric material is in the form of slabs or columns.
5. The method of claim 1, wherein the obtaining of the pseudo-plastic deformation of the ferroelectric material further comprises:
heating the ferroelectric material with the pseudo plastic deformation to a temperature higher than the phase transition temperature to eliminate the pseudo plastic deformation of the ferroelectric material; the phase transition temperature is the phase transition temperature from a low symmetry phase to a high symmetry phase of the ferroelectric material or the phase transition temperature from a ferroelectric phase to a paraelectric phase.
6. The method of claim 1, wherein the method of applying stress comprises:
the ferroelectric material is placed on a support structure and then stressed.
7. The method of claim 1, wherein the ferroelectric material comprises one or more of a sodium bismuth titanate-based ceramic, a lead zirconate titanate ceramic, and a barium titanate ceramic.
8. The method according to claim 1, wherein the rate of temperature rise is < 500 ℃/min;
the cooling speed is less than 500 ℃/min.
9. The method of claim 1, wherein the reducing temperature is a cooling to room temperature.
10. The method of claim 1, wherein the peak temperature is 30-850 ℃.
Technical Field
The invention belongs to the technical field of functional materials, and particularly relates to a method for obtaining large pseudo plastic deformation of a ferroelectric material.
Background
The ceramic material has the characteristics of high temperature resistance, corrosion resistance and high elastic modulus, and has unique advantages in high-temperature and corrosive environment applications, such as the application of buffers and drivers under extreme high-temperature and corrosion conditions. For some applications, the amount of deformation under stress is an important indicator, especially for pseudo-plastic deformation, such as in shape memory ceramic applications. Pseudo-plastic deformation describes the behavior of a material to recover from residual deformation left by the material when the external force is removed during subsequent heat treatment. However, during the course of research over the past decades, there have been limited material choices for such applications, mainly focusing on zirconia-based, lanthanum niobate, and other oxide ceramic systems, due to the fact that most ceramicsThe material mainly undergoes elastic deformation under the action of external force and is difficult to generate plastic or pseudo-plastic deformation. The generation of pseudo-plastic deformation of ceramics requires special systems with some special physical mechanisms, such as ZrO with martensitic transformation2Based ceramic, high temperature sintered ZrO2The base ceramic is martensite near room temperature, under the action of external force, the martensite generates irreversible stress-induced orientation, after the stress is removed, the oriented martensite can not be restored to the original state, and the ceramic shows structural change in a residual deformation mode. This residual deformation is maximized in the temperature range below the austenite-martensite transition temperature, and when the ceramic in which the residual deformation exists is heat-treated to its martensite-austenite transition temperature, the residual deformation in the ceramic begins to recover as a result of the martensite to austenite transition occurring in the ceramic, because such materials do not exhibit a phenomenon involving a slip process in conventional plastic deformation and exhibit a memory of the structural state prior to deformation. However, in addition to the above materials, the kinds of ceramics capable of realizing large pseudo plastic deformation are rare in practice.
Ferroelectric materials are a typical functional ceramic material, and the research and application directions of the ferroelectric materials are focused in the application fields of dielectric, piezoelectric, pyroelectric and the like. Some ferroelectric materials have ferroelasticity and can generate plastic or pseudo-plastic deformation under external force, but the deformation amount is generally small, and the research on the pseudo-plastic deformation of the corresponding subway electric materials is very little. The ferroelectric material has a wide variety of materials, the material selection range is large, and if large pseudo plastic deformation can be generated in the ferroelectric material, the functionality of the ferroelectric material can be expanded, for example, the application in the aspect of shape memory materials can be expanded, and meanwhile, the variety of structural ceramic materials is enriched.
Disclosure of Invention
In view of the above, the present invention provides a method for obtaining large pseudo-plastic deformation of a ferroelectric material, which can obtain large pseudo-plastic deformation of the ferroelectric material.
The invention provides a method for obtaining pseudo-plastic deformation of a ferroelectric material, which comprises the following steps:
under the action of stress, the ferroelectric material is subjected to heat treatment of firstly heating and then cooling, the peak temperature of the heat treatment of firstly heating and then cooling is higher than the phase transition temperature from the low symmetry phase to the high symmetry phase of the ferroelectric material or the phase transition temperature from the ferroelectric phase to the paraelectric phase, and the ferroelectric material obtains pseudo plastic deformation.
Preferably, the stress is < 1 GPa.
Preferably, the stress is such that the ferroelectric material has a strain of < 15%.
Preferably, the ferroelectric material is in a shape of a lath or a column.
Preferably, the ferroelectric material after obtaining the pseudo-plastic deformation further comprises:
heating the ferroelectric material with the pseudo plastic deformation to a temperature higher than the phase transition temperature to eliminate the pseudo plastic deformation of the ferroelectric material; the phase transition temperature is the phase transition temperature from a low symmetry phase to a high symmetry phase of the ferroelectric material or the phase transition temperature from a ferroelectric phase to a paraelectric phase.
Preferably, the method for applying stress includes:
the ferroelectric material is placed on a support structure and then stressed.
Preferably, the ferroelectric material comprises one or more of sodium bismuth titanate-based ceramic, lead zirconate titanate ceramic and barium titanate ceramic.
Preferably, the temperature rising speed is less than 500 ℃/min; .
The cooling speed is less than 500 ℃/min.
Preferably, the temperature reduction is to reduce the temperature to room temperature.
Preferably, the peak temperature is 30-850 ℃.
The invention provides a method for realizing large recoverable pseudo-plastic deformation of a ferroelectric material, which comprises the steps of applying a certain external stress on the ferroelectric material, and carrying out heating/cooling heat treatment under the condition of keeping the stress, wherein the peak temperature Tpeak of the heat treatment is higher than the phase transition temperature (Tlow-high, generally the transition temperature between a ferroelectric phase and a paraelectric phase) from a low-symmetry phase to a high-symmetry phase of the corresponding ferroelectric material; after this heat treatment, the ferroelectric material obtains significant pseudo-plastic deformation (which can exceed 0.3%) around room temperature. Meanwhile, if the ferroelectric material is heated to above the phase transition temperature, the large pseudo plastic deformation can be completely recovered, and the method for generating the large pseudo plastic deformation can be applied to various ferroelectric materials.
The invention carries out heat treatment on the ferroelectric material under the action of stress until the phase transition temperature is higher than the phase transition temperature, and then the temperature is reduced to the room temperature, so as to obtain large pseudo plastic deformation in the ferroelectric material, and the invention provides a method for realizing large recoverable plastic deformation of the ferroelectric material under the action of applied external force, which has strong operability and simpler process, and can effectively reduce the risk of ceramic fracture under the action of small stress; the generated pseudo plastic deformation can be completely recovered, and the repeatable utilization rate is high; modulus of elasticity of ZrO2About half of the base ceramic fills the material selection of small stress application occasions; the selection range of the stress buffer and the driver applying structural ceramics under extreme conditions of high temperature, corrosion and the like is enriched, and particularly the application condition of a small stress range is enriched.
Drawings
FIG. 1 shows bismuth sodium titanate-barium titanate (0.96 Na)0.5Bi0.5TiO3-0.04BaTiO3) The vertical displacement at the middle point of the span changes with the temperature when the ferroelectric material is subjected to three-point bending and external force application in the process of heat treatment to different peak temperatures under the action of stress;
FIG. 2(a) shows a bismuth sodium titanate ferroelectric material (Na)0.5Bi0.5TiO3: NBT) photograph of the film after a heat treatment at 350 ℃ under a small stress to return to room temperature;
(b) for bending bismuth sodium titanate (Na)0.5Bi0.5TiO3: NBT) photograph of the ferroelectric material after reheating to 350 ℃ under stress-free action and then returning to room temperature;
FIG. 3 shows a ferroelectric material (Na)0.5Bi0.5TiO3: NBT) deformation size after heat treatment (350 ℃) under the action of small stress and size representation when deformation is recovered after heat treatment under the action of no stress;
FIG. 4 shows a ferroelectric material ((Na)0.5Bi0.5)0.96Ba0.04TiO3: NBT4) Heat treated under Small stress (. about.35)The deformation size after 0 ℃ and the size representation of deformation recovery after heat treatment without stress;
FIG. 5 shows a ferroelectric material ((Na)0.5Bi0.5)0.5Ba0.5TiO3: NBT50) under the action of small stress after heat treatment (350 ℃) and under the action of no stress after heat treatment deformation recovery dimensional characterization;
FIG. 6 is a graph showing the deformation dimension of the soft PZT-5 ferroelectric material after heat treatment (500 ℃) under small stress and the dimension characterization when the deformation is recovered after heat treatment under no stress;
FIG. 7 is a graph showing the deformation dimension of a hard PZT-8 ferroelectric material after heat treatment (-350 deg.C) under small stress and the dimension characterization when the deformation is recovered after heat treatment without stress;
FIG. 8 shows a ferroelectric material (BaTiO)3: BT) under small stress (200 ℃) and after heat treatment under no stress (200 ℃) the deformation size is represented.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other examples, which may be modified or appreciated by those of ordinary skill in the art based on the examples given herein, are intended to be within the scope of the present invention. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention. In the examples, the methods used were all conventional methods unless otherwise specified.
The invention provides a method for obtaining large pseudo plastic deformation of a ferroelectric material, which comprises the following steps:
under the action of stress, the ferroelectric material is subjected to heat treatment of firstly heating and then cooling, the peak temperature of the heat treatment of firstly heating and then cooling is higher than the phase transition temperature from the low symmetry phase to the high symmetry phase of the ferroelectric material or the phase transition temperature from the ferroelectric phase to the paraelectric phase, and the ferroelectric material obtains pseudo plastic deformation.
In the present invention, the stress is preferably < 1GPa, more preferably 0.1-0.9 GPa, more preferably 0.2-0.8 GPa, more preferably 0.3-0.6 GPa, and most preferably 0.4-0.5 GPa.
In the present invention, the stress is preferably such that the strain of the ferroelectric material is < 15%, more preferably 1 to 12%, more preferably 5 to 10%, and most preferably 6 to 8%.
The ferroelectric material composition is not particularly limited in the present invention, and may be one or more of bismuth sodium titanate-based ceramic, lead zirconate titanate ceramic and barium titanate ceramic, and more specifically may be 0.96Na0.5Bi0.5TiO3-0.04BaTiO3、Na0.5Bi0.5TiO3：NBT、(Na0.5Bi0.5)0.96Ba0.04TiO3：NBT4、(Na0.5Bi0.5)0.5Ba0.5TiO3: NBT50, Soft PZT-5, hard PZT-8, BaTiO3: BT, and the like. The source of the ferroelectric material is not particularly limited in the present invention, and the ferroelectric material can be obtained from the market, or can be obtained by a preparation method of the ferroelectric material well known to those skilled in the art, such as a solid phase reaction method.
The shape and size of the ferroelectric material are not particularly limited by the present invention, and those skilled in the art can select a ferroelectric material with a suitable shape and size according to actual conditions to be processed according to the method provided by the present invention. In the invention, the ferroelectric material is preferably in a shape of a strip or a column, and the length of the strip ferroelectric material is preferably 20-75 mm, more preferably 30-70 mm, more preferably 40-60 mm, and most preferably 45-55 mm; the width is preferably 4-10 mm, more preferably 5-8 mm, and most preferably 6-7 mm; the thickness is preferably 0.4 to 0.8mm, more preferably 0.5 to 0.7mm, and most preferably 0.6 mm. In the invention, the diameter of the columnar ferroelectric material is preferably 4-5 mm, the length is preferably 8-15 mm, and more preferably 10-12 mm.
In the present invention, the stress is preferably applied in a manner including:
the ferroelectric material is placed on a support structure and then stressed.
In the present invention, the ferroelectric material is preferably placed on a fixed support structure.
In the present invention, the method of applying stress more preferably includes:
and applying stress to the ferroelectric material in a three-point bending mode of supporting at two ends and applying force in the middle.
In the present invention, the stress is preferably applied in such a manner that the lath-shaped ferroelectric material is bent and deformed to generate compressive deformation of the columnar ferroelectric material, and the columnar ferroelectric material may be placed on the support structure and then compressed by applying a normal stress.
In the present invention, the heat treatment preferably includes:
and heating the ferroelectric material to the peak temperature, and cooling to room temperature.
In the invention, the temperature rise speed is preferably less than 500 ℃/min, more preferably 5-400 ℃/min, more preferably 10-300 ℃/min, more preferably 50-200 ℃/min, and most preferably 100-150 ℃/min.
In the invention, the cooling speed is preferably less than 500 ℃/min, more preferably 5-400 ℃/min, more preferably 10-300 ℃/min, more preferably 50-200 ℃/min, and most preferably 100-150 ℃/min.
In the invention, the temperature of the room temperature is preferably 20-30 ℃, and more preferably 25 ℃.
In the invention, the peak temperature is preferably higher than the phase change temperature by more than 1 ℃, more preferably 5-300 ℃, more preferably 10-250 ℃, more preferably 50-200 ℃, and most preferably 100-150 ℃.
In the invention, the peak temperature is preferably 30-850 ℃, more preferably 50-800 ℃, more preferably 100-600 ℃, more preferably 200-500 ℃, more preferably 300-400 ℃, and most preferably 350 ℃.
In the present invention, the phase transition temperature from the low symmetry phase to the high symmetry phase of the ferroelectric material is generally the transition temperature from the ferroelectric phase to the paraelectric phase, and the method for obtaining the phase transition temperature is not particularly limited in the present invention, and a method for obtaining the phase transition temperature of the ferroelectric material known to those skilled in the art may be adopted, for example, the method for obtaining the phase transition temperature may be:
testing a dielectric constant-temperature curve of the ferroelectric material, and obtaining phase change temperature from the temperature of the dielectric constant mutation position; or
The ferroelectric material Differential Scanning Calorimetry (DSC) curve is tested, and the phase transition temperature is obtained according to the position of the endothermic/exothermic peak on the curve.
In the present invention, the method for obtaining the pseudo-plastic deformation of the ferroelectric material further comprises:
heating the ferroelectric material with the pseudo plastic deformation to a temperature higher than the phase transition temperature to eliminate the pseudo plastic deformation of the ferroelectric material; the phase transition temperature is the phase transition temperature from a low symmetry phase to a high symmetry phase of the ferroelectric material or the phase transition temperature from a ferroelectric phase to a paraelectric phase.
The ferroelectric material is prepared by using a traditional solid-phase reaction method, the prepared ceramic is heated to a specific temperature, then a certain external force is applied to the ceramic, and the temperature is reduced under the condition of keeping the external force. In the above process, the applied stress may be maintained during both the temperature increase and decrease. After cooling to room temperature, large pseudo-plastic deformations may occur in the ferroelectric material. Wherein the peak temperature of the heat treatment is higher than the low-temperature phase-high-temperature phase (generally ferroelectric phase-paraelectric phase) transition temperature of the corresponding ceramic. Because the ceramic is difficult to deform, a bending deformation mode is generally adopted, the sintered ceramic is cut into a lath-shaped sample after being polished and flattened, the lath-shaped sample is placed on a fixed supporting structure, and then stress is applied.
The mechanism for generating the pseudo-plastic deformation in the ceramic is stress-induced orientation or orientation accompanied with phase transformation, and the orientation or the stress-induced phase transformation of the micro-domain structure needs to reach above critical stress. Due to the characteristics of brittleness and high elastic modulus of the ceramic material, under a certain temperature condition, the risk of cracking of the ceramic material can be obviously increased by increasing the technical route of applying stress to improve the pseudo plastic deformation; and large pseudo-plastic deformation is difficult to generate under small stress. However, the critical stress of structure orientation or stress-induced phase transition is temperature dependent, and the present invention causes large pseudo-plastic deformation at small stress. Under the action of small stress, the ceramic material is subjected to heat treatment above its phase transition temperature. In the process of temperature reduction, the small stress can enable phase change caused by temperature change to be carried out in an orientation mode at the phase change temperature, when the temperature is reduced to be lower than the phase change temperature, the small stress can enable the micro-area structure to continue to be oriented, the temperature is reduced to room temperature, and larger residual deformation can be obtained when the stress is removed.
As shown in figure 1, the invention uses 0.96Na bismuth sodium titanate-based ceramic0.5Bi0.5TiO3-0.04BaTiO3For example, the change of the vertical displacement at the middle point of the span of a strip sample under the action of an external force applied in a three-point bending mode along with the temperature is measured to represent the deformation performance of the strip sample under the action of stress, the phase transition temperature of the strip sample is about 170 ℃, the temperature rise heat treatment is carried out under the same stress action, and when the heat treatment temperature is lower than the phase transition temperature, for example, 140 ℃, only small pseudo plastic deformation is generated (as shown by a line 1 in fig. 1); when the heat treatment is carried out at a temperature higher than the phase transition temperature, such as 201 ℃, large multi-deformation can be obtained, as shown by a line 2 in FIG. 1; then, the deformed ceramic is heated to a temperature above the phase transition temperature, regardless of the presence or absence of external stress, so that the deformation is gradually recovered, and the recovery amount is related to the reached temperature, and when the temperature is above the phase transition temperature, the plastic deformation is basically and completely recovered.
In the invention, the method for obtaining large pseudo plastic deformation in the ferroelectric material by heat treating the ferroelectric material to the temperature higher than the phase transition temperature thereof and then cooling to room temperature under the action of stress has the following advantages: (1) the method for realizing large recoverable plastic-like deformation of the ferroelectric material under the action of applied external force has the advantages of strong operability, simpler process and capability of effectively reducing the risk of ceramic fracture under the action of small stress; (2) the generated pseudo plastic deformation can be completely recovered, and the repeatable utilization rate is high; (3) modulus of elasticity of ZrO2About half of the base ceramic fills the material selection of small stress application occasions; the selection range of the stress buffer and the driver applying structural ceramics under extreme conditions of high temperature, corrosion and the like is enriched, and particularly the application condition of a small stress range is enriched.
The present invention providesThe method for obtaining large pseudo-plastic deformation by heat treating the ferroelectric material to the phase transition temperature of the ferroelectric material under the action of the holding stress and then cooling the ferroelectric material to the room temperature is a general method for obtaining large pseudo-plastic deformation amount in the ferroelectric material, and bismuth sodium titanate-barium titanate ((1-x) Na)0.5Bi0.5TiO3-x BaTiO3: NBT100x) based ceramic, lead zirconate titanate (PbTi)xZr1- xO3: PZT) based ceramics to illustrate the feasibility of this approach.
EXAMPLE 1 bismuth sodium titanate Na0.5Bi0.5TiO3(NBT) ceramics
The NBT ceramic samples were prepared by conventional solid phase synthesis: according to the stoichiometric proportion of Bi2O3，Na2CO3，TiO2(analytically pure, national drug group), adding alcohol, ball milling for 12 hours, drying, and keeping the temperature at 850 ℃ for 2 hours to synthesize NBT initial powder. Then adding the synthesized powder into alcohol, ball-milling for 12 hours again, drying, adding a binder (5% polyvinyl alcohol (PVA) aqueous solution) accounting for 10% of the weight of the powder, and pressing into a blank by a uniaxial compression method. Burning off the binder in the blank at a high temperature of 800 ℃, and then putting the blank into a muffle furnace to be sintered at a temperature of 1140 ℃ for 2 hours. The sintered ceramic was surface-polished so that both end faces thereof were parallel, and then cut into a slab-like sample (dimensions 75mm × 6.6mm × 0.85 mm).
The sample is fixed by a three-point bending mode of supporting at two ends and applying force in the middle, and the phase transition temperature of the material is about 301 ℃. And (3) carrying out heat treatment of firstly heating and then cooling with the peak temperature of 350 ℃, wherein the stress action is kept in the process of cooling. The ceramic after heat treatment under stress produced significant bending deformation, and figure 2(a) shows a photograph of a bent real object, and the deformation was substantially recovered by subsequent heat treatment under no stress (heating to 301 ℃ or higher), as shown in figure 2 (b).
The bending deformation at room temperature can be measured by:
before bending deformation or after bending recovery, the ceramic is in a straight configuration, and when the ceramic is placed on a flat plate, the distance change from each point on the middle line of the upper surface along the length direction to the flat plate is small. After bending, the test plate is placed on a marble base plate, the convex side faces upwards, and the height from each point of the upper surface of the strip sample of the test plate, which is equidistant along the middle line of the length direction, to the base plate is measured, and the change of the height reflects the bending condition of the sample. The dimensional changes tested in the bent state and in the state after bend recovery are shown in fig. 3, and recoverable pseudo-plastic deformations produced in the ceramic can be characterized by such tests.
The ceramic prepared in example 1 was cut into a columnar sample (8 mm. times.4 mm in size), and the columnar sample was compressed by applying pressure in the thickness direction, and the phase transition temperature of this material was about 301 ℃. And (3) carrying out heat treatment of firstly heating and then cooling with the peak temperature of 350 ℃, and keeping the effect of stress in the cooling process. After heat treatment under stress, the ceramic produced significant compressive deformation (0.22%) near room temperature, and after subsequent heat treatment under stress (heating to over 301 ℃), the deformation was substantially recovered. The compression set at room temperature and its recovery can be measured by directly testing the thickness dimensional change.
EXAMPLE 2 bismuth sodium titanate-barium titanate (1-x) Na0.5Bi0.5TiO3-xBaTiO3: NBT100x ceramic, x ═ 0.04, 0.5
NBT4 and NBT50 ceramic samples were prepared by conventional solid phase synthesis methods as in example 1. The sintered ceramic was surface-polished so that both end surfaces thereof were parallel, and then cut into a slab sample (the size of NBT4 ceramic was about 75 mm. times.8 mm. times.0.87 mm, and the size of NBT50 ceramic was about 75 mm. times.6.5 mm. times.1.0 mm).
Fixing a sample by using a three-point bending mode of supporting at two ends and applying force in the middle, then carrying out heat treatment of firstly heating and then cooling with the peak value higher than the phase transition temperature of the corresponding component ceramic, and applying holding force in the heat treatment process.
The NBT4 and NBT50 ceramics may have a phase transition temperature of 160 ℃ and 203 ℃ and a heat treatment peak temperature of 350 ℃. Under the action of stress, NBT4 and NBT50 ceramics respectively undergo heat treatment of raising temperature and then reducing temperature with the peak value of 350 ℃, and then obtain obvious bending deformation near room temperature.
The test was carried out according to the method of example 1, the test results being shown in the height variations from the points equally spaced on the line on the upper surface of the ceramic to the base plate as tested in fig. 4 and 5, and after a subsequent heat treatment under stress-free conditions (heating to above the transformation temperature), the deformation was substantially recovered, as shown in fig. 4 and 5.
EXAMPLE 3 PZT-based lead zirconate titanate ceramics
PZT-based ceramic sample: soft doped PZT-5 and hard doped PZT-8 ceramics are commercially available ceramics. The purchased PZT ceramics were surface-polished so that both end faces thereof were parallel, and then cut into slab-like samples (the dimensions of PZT-5 and PZT-8 ceramics were 60 mm. times.10 mm. times.1 mm).
Fixing a sample by using a three-point bending mode of supporting at two ends and applying force in the middle, then carrying out heat treatment of firstly heating and then cooling with the peak value higher than the phase transition temperature of the corresponding component ceramic, and applying holding force in the heat treatment process.
For PZT-5 and PZT-8 ceramics, the phase transition temperature is 170 ℃ and 300 ℃, the peak temperature of the heat treatment is 500 ℃, and after the PZT-5 and PZT-8 ceramics are subjected to the heat treatment with the peak temperature of 500 ℃ under the action of stress, obvious bending deformation is obtained near room temperature.
The measurements were carried out according to the method of example 1, and the results are shown in FIGS. 6 and 7 as the height variations from equally spaced points on the line on the upper surface of the ceramic to the flat plate of the substrate. After subsequent heat treatment (heating to above the transformation temperature) under no stress, the deformation is substantially recovered, as shown in fig. 6 and 7.
Example 4 barium titanate BT ceramic.
BaTiO3(BT) ceramic samples were prepared by conventional solid phase synthesis methods as in example 1. The ferroelectric-paraelectric phase transition temperature of the BT ceramic is about 130 ℃. The sintered ceramic was surface-polished so that both end faces thereof were parallel, and then cut into a slab-like sample (size 25mm × 6mm × 0.9 mm).
Fixing the sample by using a three-point bending mode of supporting at two ends and applying force in the middle, then carrying out heat treatment of firstly raising the temperature and then lowering the temperature at the peak value of 200 ℃, and applying holding force in the heat treatment process.
After the BT ceramic is subjected to heat treatment at the peak value of 200 ℃ under the action of stress, obvious bending deformation is obtained near room temperature. The results of the measurements according to the test method of example 1 are shown in fig. 8 as the height change from the points equally spaced on the line on the upper surface of the ceramic to the flat plate of the substrate. After subsequent heat treatment (heating to above the transformation temperature) under stress-free conditions, the deformation substantially recovers, as shown in fig. 8.
The invention provides a method for realizing large recoverable pseudo-plastic deformation of a ferroelectric material, which comprises the steps of applying a certain external stress on the ferroelectric material, and carrying out heating/cooling heat treatment under the condition of keeping the stress, wherein the peak temperature Tpeak of the heat treatment is higher than the phase transition temperature (Tlow-high, generally the transition temperature between a ferroelectric phase and a paraelectric phase) from a low-symmetry phase to a high-symmetry phase of the corresponding ferroelectric material; after this heat treatment, the ferroelectric material obtains significant pseudo-plastic deformation (which can exceed 0.3%) around room temperature. Meanwhile, if the ferroelectric material is heated to above the phase transition temperature, the large pseudo plastic deformation can be completely recovered, and the method for generating the large pseudo plastic deformation can be applied to various ferroelectric materials.
While only the preferred embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.