Lead-free ferroelectric ceramic with high electrostriction coefficient and preparation method thereof

Abstract

The invention discloses a lead-free ferroelectric ceramic with a high electrostriction coefficient and a preparation method thereof, the chemical formula of the lead-free ferroelectric ceramic is Ba (Zr < 0.25 > Ti < 0.75 >) O < 3-x > (Ba < 0.7 > Ca < 0.3 >) TiO3, and x is more than 0.49 and less than 0.51; the preparation method comprises the following steps: 1, selecting raw materials; 2, respectively ball-milling the raw materials, mixing, drying and sieving; 3, pre-sintering treatment; 4, pelletizing after ball milling; 5, pressing a green body; and 6, sintering treatment. The tetragonal phase and orthogonal phase coexisting lead-free ferroelectric ceramic is obtained by doping different contents of tetragonal phase (Ba0. 7Ca0. 3) TiO3 into trilateral phase Ba (Zr0. 25Ti0. 75) O3, the crystal lattice stability is remarkably reduced by utilizing the symmetry of a multiphase coexisting crystal structure, the electrostriction coefficient of the lead-free ferroelectric ceramic is improved, and the lead-free ferroelectric ceramic is suitable for the fields of high-precision drivers, sensors and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic ceramic materials, and in particular relates to a lead-free ferroelectric ceramic with a high electrostrictive coefficient and a preparation method thereof. Background Art

[0002] The electrostrictive effect is a phenomenon in which dielectric materials produce mechanical strain under the action of an external electric field. The magnitude of the strain is proportional to the square of the electric field strength. This characteristic has important application value in the fields of micro-displacement actuators and sensors. However, the electrostrictive coefficient of most dielectric materials is Q 33 The electrostrictive coefficient is generally low, which limits its practical application in high-precision electromechanical systems. In recent years, researchers have been committed to improving the electrostrictive coefficient through methods such as defect doping and multi-field coupling optimization. Q 33 However, the design of high electrostrictive coefficients remains a bottleneck. Existing methods for increasing the electrostrictive coefficient often rely on a labor-intensive trial-and-error method involving doping, which is inefficient and lacks a clear goal. Therefore, a general design method for improving the electrostrictive coefficient is still lacking. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a lead-free ferroelectric ceramic with high electrostrictive coefficient in view of the above-mentioned shortcomings of the prior art. 0.25 Ti 0.75 )O3 doped with different contents of tetragonal phase (Ba 0.7 Ca 0.3 )TiO3 regulates the symmetry of the crystal structure and obtains lead-free electric ceramics with coexistence of tetragonal phase and orthorhombic phase at room temperature. The symmetry of the crystal structure of multi-phase coexistence is used to significantly reduce the lattice stability, improve the electrostriction coefficient of lead-free ferroelectric ceramics, and solve the problem of too low electrostriction coefficient of existing dielectric materials.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a lead-free ferroelectric ceramic with high electrostrictive coefficient, characterized in that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3, and 0.49< x <0.51.

[0005] During the research process of this invention, the modified elastic Gibbs free energy of the ferroelectric system was first derived theoretically. G , whose expression is:

[0006] in, α 、 β and γ is the Landau free energy coefficient, P is the order parameter polarization of the ferroelectric material, s is the elastic compliance, Q represents the electrostrictive coefficient.

[0007] In formula (1), when the system is in a multiphase coexistence state, ; When the system is single-phase, Therefore and Therefore, theoretical deduction shows that compared with single-phase ferroelectric ceramics, multi-phase coexisting ferroelectric ceramics have a larger electrostriction coefficient. Based on this theoretical derivation, the electrostriction coefficient can be improved by designing multi-phase coexisting ferroelectric ceramics.

[0008] The present invention designs a lead-free ferroelectric ceramic system Ba(Zr 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3, and 0.49< x <0.51, through the rhombohedral Ba(Zr 0.25 Ti 0.75 )O3 doped with different contents of tetragonal phase (Ba 0.7 Ca 0.3 )TiO3( x =0.3, 0.4, 0.45, 0.49, 0.5, 0.6, 0.7……), regulating the symmetry of the crystal structure, and the performance test results show that when x = 0.3, 0.4, 0.45, 0.49, 0.6 and 0.7, the lead-free ferroelectric ceramics exhibit a single-phase crystal structure (tetragonal, orthorhombic or rhombohedral) at room temperature. x When the ratio is less than 0.51, the lead-free ferroelectric ceramics exhibit a multi-phase coexistence crystal structure (tetragonal phase and orthorhombic phase coexistence) at room temperature. Since the multi-phase coexistence crystal structure (tetragonal phase and orthorhombic phase coexistence) significantly reduces the lattice stability, the multi-phase coexistence ferroelectric ceramics have a higher electrostriction coefficient than the single-phase ferroelectric ceramics.

[0009] The above-mentioned high electrostrictive coefficient lead-free ferroelectric ceramic is characterized in that the electrostrictive coefficient of the lead-free ferroelectric ceramic at room temperature is greater than 0.07m 4 / C 2 .

[0010] The above-mentioned high electrostrictive coefficient lead-free ferroelectric ceramic is characterized in that it has the characteristic of coexistence of multiple crystal structure symmetries.

[0011] The above-mentioned high electrostrictive coefficient lead-free ferroelectric ceramic is characterized in that it has the characteristics of coexistence of tetragonal phase and orthorhombic phase symmetry.

[0012] At the same time, the present invention also discloses a method for preparing the above-mentioned lead-free ferroelectric ceramic with high electrostrictive coefficient, characterized in that the method comprises the following steps: Step 1: According to the chemical formula of the target product lead-free ferroelectric ceramic, raw materials BaCO3, BaZrO3, CaCO3 and TiO2 are selected for drying and weighing; the drying temperature is 120°C and the drying time is 8 hours; Step 2: The raw materials BaCO3, BaZrO3, CaCO3 and TiO2 weighed in step 1 are ball-milled separately, and then the ball-milled raw materials are mixed and dried, and the zirconia grinding balls are removed by sieving to obtain a mixed powder; the ball milling uses zirconia grinding balls and anhydrous ethanol as solvent, the ball milling speed is 600 r / min, and the time is 12 hours; Step 3: pre-sintering the mixed powder obtained in step 2, and then cooling the furnace to obtain a pre-sintered blank; the pre-sintering process is performed at a heating rate of 3°C / min, a temperature of 1350°C, and a holding time of 3h; Step 4: ball-milling the pre-sintered blank obtained in step 3 to obtain ball-milled powder, and then granulating the ball-milled powder to obtain ceramic particles; the ball milling speed is 600 r / min, the time is 12 h, and the binder used in the granulation is 5% by mass of polyvinyl alcohol (PVA); Step 5: Pressing the ceramic particles obtained in step 4 into a green body, and then performing a binder removal treatment on the green body, and then furnace cooling; the pressing pressure is 5 MPa, the pressure holding time is 1 min, the debinding treatment is performed at a heating rate of 1 ° C / min, the temperature is 500 ° C, and the holding time is 5 h; Step 6: Sinter the green body after the binder removal treatment in step 5, and then cool it in a furnace to obtain a lead-free ferroelectric ceramic; the sintering treatment is performed at a heating rate of 3°C / min, a temperature of 1450°C, and a holding time of 3h.

[0013] The above method is characterized in that the performance test of the lead-free ferroelectric ceramic obtained in step 6 is performed, comprising the following steps: Step 601: Using a dielectric temperature spectrum testing system to measure the dielectric temperature spectrum of the lead-free ferroelectric ceramic to determine the phase transition temperature of the lead-free ferroelectric ceramic; Step 602: characterize the crystal structure symmetry of the lead-free ferroelectric ceramic at room temperature using an X-ray diffractometer; Step 603: Draw the composition-temperature-structure phase of the lead-free ferroelectric ceramic according to the phase transition temperature in step 601 and the crystal structure symmetry in step 602; Step 604: Test the hysteresis loop and electrostrain curve of the lead-free ferroelectric ceramic at room temperature, and obtain the electrostriction coefficient by fitting.

[0014] Compared with the prior art, the present invention has the following advantages: 1. The lead-free ferroelectric ceramics of the present invention are formed by the rhombohedral Ba(Zr 0.25 Ti 0.75 )O3 doped with different contents of tetragonal phase (Ba 0.7 Ca 0.3 )TiO3 regulates the crystal structure symmetry and obtains the coexistence of tetragonal and orthorhombic phases of Ba(Zr 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3, using the symmetry of the crystal structure of multi-phase coexistence to significantly reduce the lattice stability and improve the electrostriction coefficient of lead-free ferroelectric ceramics.

[0015] 2. Ba(Zr) designed and prepared by the present invention 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3 lead-free ferroelectric ceramics exhibit excellent electrostriction coefficient ( Q 33 >0.07m 4 / C 2 ), which is significantly higher than other existing ferroelectric ceramic systems, providing a universal design method for improving the electrostriction coefficient of dielectric materials.

[0016] 3. The design method of the present invention for improving the electrostrictive coefficient by utilizing a multi-phase coexisting crystal structure is universal and can be applied to improving the electrostrictive properties of other dielectric materials.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a comparison chart of the dielectric temperature spectra of the lead-free ferroelectric ceramics prepared in Example 1 of the present invention and Comparative Examples 1, 2, and 5.

[0019] Figure 2 The following are comparative diagrams of characteristic X-ray diffraction of lead-free ferroelectric ceramics prepared in Comparative Examples 2, 4 and 5 of the present invention at room temperature.

[0020] Figure 3 The composition-temperature-structure phase diagram of the lead-free ferroelectric ceramics prepared in Example 1 and Comparative Examples 1-6 of the present invention.

[0021] Figure 4 1. A comparison diagram of the hysteresis loop, electrostrain curve and electrostriction coefficient of the lead-free ferroelectric ceramics prepared in Example 1 of the present invention and Comparative Examples 1, 2, 5 and 6.

[0022] Figure 5 This is a comparison chart of the electrostriction coefficients of the lead-free ferroelectric ceramic prepared in Example 1 of the present invention and other existing ferroelectric ceramic systems. DETAILED DESCRIPTION

[0023] Example 1 The chemical formula of the lead-free ferroelectric ceramic of this embodiment is Ba(Zr 0.25 Ti 0.75 )O3-0.5(Ba 0.7 Ca 0.3 )TiO3.

[0024] The preparation method of the lead-free ferroelectric ceramic of this embodiment comprises the following steps: Step 1: Select the raw material BaCO according to the chemical formula composition of the target product lead-free ferroelectric ceramic. 3、 BaZrO3, CaCO3 and TiO2 are dried and weighed; the drying temperature is 120°C and the drying time is 8 hours; Step 2: weigh the raw material BaCO 3、 BaZrO3, CaCO3 and TiO2 were ball-milled separately, and the ball-milled raw materials were then mixed and dried. After sieving to remove the zirconia grinding balls, a mixed powder was obtained. The ball milling used zirconia grinding balls and anhydrous ethanol as solvent at a speed of 600 r / min for 12 hours. Step 3: pre-sintering the mixed powder obtained in step 2, and then cooling the furnace to obtain a pre-sintered blank; the pre-sintering process is performed at a heating rate of 3°C / min, a temperature of 1350°C, and a holding time of 3h; Step 4: ball-milling the pre-sintered blank obtained in step 3 to obtain ball-milled powder, and then granulating the ball-milled powder to obtain ceramic particles; the ball milling speed is 600 r / min, the time is 12 h, and the binder used in the granulation is 5% by mass of polyvinyl alcohol (PVA); Step 5: Pressing the ceramic particles obtained in step 4 into a green body, and then performing a binder removal treatment on the green body, and then furnace cooling; the pressing pressure is 5 MPa, the pressure holding time is 1 min, the debinding treatment is performed at a heating rate of 1 ° C / min, the temperature is 500 ° C, and the holding time is 5 h; Step 6: Sinter the green body after the binder removal treatment in step 5, and then cool it in a furnace to obtain a lead-free ferroelectric ceramic; the sintering treatment is performed at a heating rate of 3°C / min, a temperature of 1450°C, and a holding time of 3h.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.3(Ba 0.7 Ca 0.3 )TiO3.

[0026] Comparative Example 2 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.4(Ba 0.7 Ca 0.3 )TiO3.

[0027] Comparative Example 3 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.45(Ba 0.7 Ca 0.3 )TiO3.

[0028] Comparative Example 4 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.49(Ba 0.7 Ca 0.3 )TiO3.

[0029] Comparative Example 5 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.6(Ba 0.7 Ca 0.3 )TiO3.

[0030] Comparative Example 6 The difference between this comparative example and Example 1 is that the chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3-0.7(Ba 0.7 Ca 0.3 )TiO3.

[0031] The performance test of the lead-free ferroelectric ceramics prepared in Example 1 and Comparative Examples 1 to 6 of the present invention comprises the following steps: Step 601: Using a dielectric temperature spectrum testing system to measure the dielectric temperature spectrum of the lead-free ferroelectric ceramic to determine the phase transition temperature of the lead-free ferroelectric ceramic; Step 602: characterize the crystal structure symmetry of the lead-free ferroelectric ceramic at room temperature using an X-ray diffractometer; Step 603: Draw the composition-temperature-structure phase of the lead-free ferroelectric ceramic according to the phase transition temperature in step 601 and the crystal structure symmetry in step 602; Step 604: Test the hysteresis loop and electrostrain curve of the lead-free ferroelectric ceramic at room temperature, and obtain the electrostriction coefficient by fitting.

[0032] Figure 1 The dielectric temperature spectrum comparison diagram of the lead-free ferroelectric ceramics prepared in Example 1 of the present invention and Comparative Examples 1, 2, and 5 is shown in FIG. Figure 1 It can be seen that the lead-free ferroelectric ceramic prepared in Example 1 undergoes ferroelectric-ferroelectric phase transition at room temperature, while the lead-free ferroelectric ceramics prepared in Comparative Examples 1, 2 and 5 do not undergo ferroelectric-ferroelectric phase transition at room temperature.

[0033] Figure 2 The characteristic X-ray diffraction comparison diagram of the lead-free ferroelectric ceramics prepared in Comparative Examples 2, 4 and 5 of the present invention at room temperature is shown in FIG. Figure 2 It can be seen that the lead-free ferroelectric ceramic prepared in Comparative Example 5 exhibits a tetragonal crystal structure at room temperature, the lead-free ferroelectric ceramic prepared in Comparative Example 4 exhibits an orthorhombic crystal structure at room temperature, and the lead-free ferroelectric ceramic prepared in Comparative Example 2 exhibits a rhombohedral crystal structure at room temperature.

[0034] Figure 3 The composition-temperature-structure phase diagram of the lead-free ferroelectric ceramics prepared in Example 1 and Comparative Examples 1 to 6 of the present invention is shown in FIG. Figure 3 It can be seen that the Ba(Zr 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3 system in x =0.5 component (0.49< x <0.51) are all close to the crystal structure of multiphase coexistence.

[0035] Figure 4 The hysteresis loop, electrostrain curve and electrostriction coefficient comparison diagram of the lead-free ferroelectric ceramics prepared in Example 1 of the present invention and Comparative Examples 1, 2, 5 and 6 are shown in FIG. Figure 4 It can be seen that compared with the single-phase crystal structure ( x =0.3, 0.4, 0.6, 0.7), multi-phase coexistence crystal structure (0.49<x <0.51) has a larger electrostrictive coefficient.

[0036] Figure 5 This is a comparison of the electrostrictive coefficients of the lead-free ferroelectric ceramic prepared in Example 1 of the present invention and other existing electroceramic systems. Figure 5 It can be seen that the electrostrictive coefficient of the lead-free ferroelectric ceramic at room temperature is 0.072m 4 / C 2 , significantly higher than other existing ferroelectric ceramic systems.

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A lead-free ferroelectric ceramic with a high electrostrictive coefficient, characterized in that: The chemical formula of the lead-free ferroelectric ceramic is Ba(Zr 0.25 Ti 0.75 )O3- x (Ba 0.7 Ca 0.3 )TiO3, and 0.49< x <0.

51.

2. The high electrostrictive coefficient lead-free ferroelectric ceramic according to claim 1, characterized in that: The electrostriction coefficient of the lead-free ferroelectric ceramic at room temperature is greater than 0.07m 4 / C 2 .

3. The high electrostrictive coefficient lead-free ferroelectric ceramic according to claim 1, characterized in that: The high electrostrictive coefficient lead-free ferroelectric ceramic has the characteristic of coexistence of multiple crystal structure symmetries.

4. A high electrostrictive coefficient lead-free ferroelectric ceramic according to claim 3, characterized in that: The high electrostrictive coefficient lead-free ferroelectric ceramic has the characteristics of coexistence of tetragonal phase and orthorhombic phase symmetry.

5. A method for preparing the high electrostrictive coefficient lead-free ferroelectric ceramic according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1: According to the chemical formula of the target product lead-free ferroelectric ceramic, raw materials BaCO3, BaZrO3, CaCO3 and TiO2 are selected for drying and weighing; the drying temperature is 120°C and the drying time is 8 hours; Step 2: The raw materials BaCO3, BaZrO3, CaCO3 and TiO2 weighed in step 1 are ball-milled separately, and then the ball-milled raw materials are mixed and dried, and the zirconia grinding balls are removed by sieving to obtain a mixed powder; the ball milling uses zirconia grinding balls and anhydrous ethanol as solvent, the ball milling speed is 600 r / min, and the time is 12 hours; Step 3: pre-sintering the mixed powder obtained in step 2, and then cooling the furnace to obtain a pre-sintered blank; the pre-sintering process is performed at a heating rate of 3°C / min, a temperature of 1350°C, and a holding time of 3h; Step 4: ball-milling the pre-sintered blank obtained in step 3 to obtain ball-milled powder, and then granulating the ball-milled powder to obtain ceramic particles; the ball milling speed is 600 r / min, the time is 12 h, and the binder used in the granulation is 5% by mass of polyvinyl alcohol (PVA); Step 5: Pressing the ceramic particles obtained in step 4 into a green body, and then performing a binder removal treatment on the green body, and then furnace cooling; the pressing pressure is 5 MPa, the pressure holding time is 1 min, the debinding treatment is performed at a heating rate of 1 ° C / min, the temperature is 500 ° C, and the holding time is 5 h; Step 6: Sinter the green body after the binder removal treatment in step 5, and then cool it in a furnace to obtain a lead-free ferroelectric ceramic; the sintering treatment is performed at a heating rate of 3°C / min, a temperature of 1450°C, and a holding time of 3h.

6. The method according to claim 5, characterized in that The performance test of the lead-free ferroelectric ceramic obtained in step 6 comprises the following steps: Step 601: Using a dielectric temperature spectrum testing system to measure the dielectric temperature spectrum of the lead-free ferroelectric ceramic to determine the phase transition temperature of the lead-free ferroelectric ceramic; Step 602: characterize the crystal structure symmetry of the lead-free ferroelectric ceramic at room temperature using an X-ray diffractometer; Step 603: Draw the composition-temperature-structure phase of the lead-free ferroelectric ceramic according to the phase transition temperature in step 601 and the crystal structure symmetry in step 602; Step 604: Test the hysteresis loop and electrostrain curve of the lead-free ferroelectric ceramic at room temperature, and obtain the electrostriction coefficient by fitting.

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