Hybrid unconventional ferroelectric ceramic material with layered perovskite structure and preparation method thereof

Abstract

The invention discloses a hybrid unconventional ferroelectric ceramic material with a layered perovskite structure and a preparation method thereof, the chemical formula of the ceramic material is Sr < 1 + x > Ln < 2-x > Sc < 2 > O < 7 >, Ln = one or more of Nd, Sm and Eu, 0.0 lt, xlt; and preferably, Sr < 1.05 > Nd < 1.95 > Sc < 2O7 >, Sr < 1.1 > Sm < 1.9 > Sc < 2O7 > and Sr < 1.15 > Eu < 1.85 > Sc < 2O7 > are selected. The preparation method comprises the following steps: (a) proportioning the raw materials of SrCO3, Nd2O3, Sm2O3, Eu2O3 and Sc2O3 according to the chemical formula of Sr1.05Nd1.95Sc2O7, Sr1.1 Sm1.9Sc2O7 and Sr1.15Eu1.85Sc2O7, carrying out ball milling, drying and sieving; (b) calcining the powder prepared in the step (a), performing secondary ball milling, and sieving; and (c) adding an adhesive into the powder prepared in the step (b), tabletting, removing plastic, and sintering to obtain the ceramic material. Under the test conditions of room temperature, the test frequency of 2Hz and the added highest electric field of 400kV / cm, the residual ferroelectric polarization value measured by the Sr1. 05Nd1. 95Sc2O7 ceramic is 0.9-1.1 [mu] C / cm < 2 >, the residual ferroelectric polarization value measured by the Sr1. 1Sm1. 9Sc2O7 ceramic is 2-3 [mu] C / cm < 2 >, and the residual ferroelectric polarization value measured by the Sr1. 15Eu1. 85Sc2O7 ceramic is 0.5-0.75 [mu] C / cm < 2 >.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional ceramic materials, and relates to a ferroelectric ceramic material and a preparation method thereof, in particular to a hybrid unconventional ferroelectric ceramic material with a layered perovskite structure and a preparation method thereof. Background Art

[0002] In the information age, the development of electronic components is being driven towards miniaturization, lightweight, and integration. Information storage components urgently need to improve storage speed, storage density, and reduce storage energy consumption. Scientists have tried to develop various storage medium materials. Ferroelectric materials,凭借 their unique physical properties, such as the reversible flipping of the polarization direction of spontaneous polarization under the action of an external electric field, have become the focus of research in the field of modern information storage technology. These properties make ferroelectric materials show great potential in the development of high-density, non-volatile memories. At present, there have been many research reports on conventional ferroelectric materials. The spontaneous polarization of conventional ferroelectric materials originates from the second-order Jahn-Teller effect. However, cations with empty d orbitals or lone pair electrons are prerequisites for the second-order Jahn-Teller effect, which will greatly limit the types of ferroelectric oxides. Therefore, in order to further enrich the types of ferroelectric materials, hybrid unconventional ferroelectric materials have attracted great interest from researchers. Based on the simple perovskite structure, a series of layered perovskite structure materials can be derived. In recent years, researchers have found that this type of material has a new type of hybrid unconventional ferroelectricity. Hybrid unconventional ferroelectricity originates from the second-order ferroelectric order induced by non-polar modes such as oxygen octahedron distortion, and does not require the second-order Jahn-Teller effect active ions required for conventional ferroelectricity. Exploring ferroelectricity in materials with a layered perovskite structure is of great scientific and practical significance for broadening the research scope of hybrid unconventional ferroelectricity and deepening the understanding of its mechanism. Summary of the Invention

[0003] The reported hybrid unconventional ferroelectric ceramic material system with a layered perovskite structure needs to be further developed. Based on this, the purpose of the present invention is to provide a hybrid unconventional ferroelectric ceramic material with a layered perovskite structure and a preparation method thereof. On the basis of component design, by adjusting the chemical stoichiometric ratio, the generation of a second phase is avoided, and a completely single target component ferroelectric ceramic material is obtained.

[0004] In the first aspect, the present invention provides a hybrid unconventional ferroelectric ceramic material with a layered perovskite structure. The chemical formula of the ceramic is Sr 1+x Ln 2-x Sc2O7 (Ln = Nd, Sm, Eu; 0.0 < x < 0.2), preferably Sr 1.05 Nd 1.95 Sc2O7, Sr 1.1 Sm 1.9Sc2O7、Sr 1.15 Eu 1.85 Sc2O7.

[0005] In a second aspect, the present invention provides a method for preparing a hybrid unconventional ferroelectric ceramic material having a layered perovskite structure, the preparation method comprising the following steps:

[0006] (1) The raw materials SrCO3, Nd2O3, Sm2O3, Eu2O3 and Sc2O3 are prepared according to the chemical formula Sr 1.05 Nd 1.95 Sc2O7、Sr 1.1 Sm 1.9 Sc2O7 or Sr 1.15 Eu 1.85 Sc2O7 ingredients are ball-milled, dried and sieved.

[0007] (2) calcining the powder obtained in step (1), drying, grinding, granulating and sieving after secondary ball milling to obtain a powder with uniform particles.

[0008] (3) adding a binder to the powder obtained in step (2) and pressing it into a cylindrical green body, and then sintering it after plastic removal to obtain the hybrid unconventional ferroelectric ceramic material with a layered perovskite structure.

[0009] Furthermore, in step (1) and step (2), the ball milling method is wet ball milling, anhydrous ethanol is used as the ball milling medium, the mass ratio of the material, the grinding balls and the anhydrous ethanol during ball milling is 1:2:(0.5-1.5), and the ball milling time is 12-36 hours, preferably 24 hours.

[0010] Furthermore, in step (2), the calcination temperature is 900-1000° C. and the calcination time is 3-9 hours, preferably 1000° C. and 6 hours.

[0011] Furthermore, in step (3), the adhesive is a polyvinyl alcohol aqueous solution (PVA) with a concentration of 8 wt%, and the added amount is 5-15% of the mass of the ceramic powder, preferably 8-12%, and the molding temperature is 500-800°C, 1-3 hours, preferably 600°C, and the time is 2-3 hours.

[0012] Furthermore, in step (3), the sintering is performed by burying the green body in a crucible filled with powder having the same composition as the green body, the sintering temperature is 1450°C to 1550°C, the holding time is 3 to 12 hours, and the heating rate is 5 to 10°C / min.

[0013] The hybrid unconventional ferroelectric ceramic material with a layered perovskite structure obtained by the preparation method of the present invention has excellent ferroelectric properties, and a complete hysteresis loop can be measured at room temperature. Under the test conditions of 2Hz and a maximum applied electric field of 400kV / cm, Sr 1.1 Sm 1.9 The residual polarization value of Sc2O7 ceramics measured is 2~3μC / cm 2 , Sr. 1.05 Nd 1.95 The residual polarization value of Sc2O7 ceramics measured is 0.9~1.1μC / cm 2 , Sr. 1.15 Eu 1.85 The residual polarization value of Sc2O7 ceramics is 0.5~ 0.75μC / cm 2 The present invention can obtain a completely single target component ferroelectric ceramic material without a second phase, further enriching the types of hybrid unconventional ferroelectric materials; the preparation process of the present invention is simple and has good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1a , Figure 1b , Figure 1c They are the Rietveld fitting results of the X-ray diffraction diagrams of the ceramic samples of Examples 1-3 respectively;

[0015] Figure 2 The surface microscopic morphology of Examples 1-3;

[0016] Figure 3a , Figure 3b , Figure 3c They are typical hysteresis loops of the ceramic samples of Examples 1-3 measured at room temperature. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. The specific process parameters and the like in the following examples are only examples in a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​in the following examples. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0018] Example 1: The chemical composition of the ferroelectric ceramic is: Sr 1.1 Sm 1.9 Sc2O7

[0019] (1) Using SrCO3 (99.95%), Sm2O3 (99.99%), and Sc2O3 (99.99%) powders as raw materials, the raw material powders were mixed and weighed according to the corresponding stoichiometric ratio.

[0020] (2) The weighed raw materials were placed in a ball milling jar, and the ball milling medium was anhydrous ethanol. The raw materials, zirconium balls and anhydrous ethanol were mixed in a mass ratio of 1:2:1 and then ball milled for 24 hours. After the ball milling was completed, they were dried and passed through a 120-mesh sieve.

[0021] (3) Pour the sieved powder into a crucible and pre-calculate in air at 1000°C for 6 hours to obtain the desired target product. Then, the calcined powder is mixed with the material, zirconium balls and anhydrous ethanol in a mass ratio of 1:2:1 and ball-milled for a second time for 24 hours. After drying, the powder is ground and sieved with a 120-mesh sieve.

[0022] (4) Add 8 wt% PVA as a binder to the obtained mixed powder for granulation. The added amount is 10% of the mass of the ceramic powder. After granulation, the powder is sieved through a 40-mesh sieve and an 80-mesh sieve to obtain a powder with uniform particles. The powder is pressed into a cylindrical body with a diameter of 12 mm and a thickness of about 1.5 mm at a pressure of 100 MPa. The body is then sintered at 600°C for 2 hours to obtain a once-sintered body.

[0023] (5) The primary sintered green body is buried in a crucible filled with powder having the same composition as the green body, the temperature is raised to 1550°C at a rate of 5°C / min and kept at this temperature for 6 hours, the temperature is lowered to 1100°C at a rate of 2°C / min, and the green body is taken out after being cooled to room temperature in the furnace, thereby obtaining the desired dense layered perovskite-like hybrid unconventional ferroelectric ceramic material.

[0024] The ceramic samples prepared in Example 1 were subjected to X-ray diffraction analysis and the results are shown in the attached Figure 1a It can be seen from the figure that the ceramic sample of Example 1 obtained has no impurity phase.

[0025] The sintered surface of the ceramic sample prepared in Example 1 was analyzed by scanning electron microscopy, and the obtained surface morphology is shown in the attached Figure 2 , it can be seen from the figure that the ceramic surface is dense.

[0026] The surface of the ceramic sample prepared in Example 1 was ground, thinned, and gold-sprayed, and then the ferroelectric performance was tested using a ferroelectric tester. The test frequency was 2 Hz, and the maximum electric field applied was 400 kV / cm. The typical hysteresis loop measured at room temperature is shown in the attached figure. Figure 3a .

[0027] Example 2: The chemical composition of the ferroelectric ceramic is: Sr 1.05 Nd 1.95 Sc2O7

[0028] SrCO3 (99.95%), Nd2O3 (99.99%), and Sc2O3 (99.99%) powders were used as raw materials, and the raw material powders were mixed and weighed according to the corresponding stoichiometric ratio. The preparation method of Example 1 was repeated according to the above formula.

[0029] The ceramic samples prepared in Example 2 were subjected to X-ray diffraction analysis and the results are shown in the attached Figure 1b It can be seen from the figure that the ceramic of Example 2 obtained has no impurity phase.

[0030] The sintered surface of the ceramic sample prepared in Example 2 was analyzed by scanning electron microscopy, and the obtained surface morphology is shown in the attached Figure 2 , it can be seen from the figure that the ceramic surface is dense.

[0031] The surface of the ceramic sample prepared in Example 2 was ground, thinned, and gold-sprayed, and then the ferroelectric performance was tested using a ferroelectric tester. The test frequency was 2 Hz, and the maximum electric field applied was 400 kV / cm. The typical hysteresis loop measured at room temperature is shown in the attached figure. Figure 3b .

[0032] Example 3: The chemical composition of the ferroelectric ceramic is: Sr 1.15 Eu 1.85 Sc2O7

[0033] SrCO3 (99.95%), Eu2O3 (99.99%), and Sc2O3 (99.99%) powders were used as raw materials, and the raw material powders were mixed and weighed according to the corresponding stoichiometric ratio. The preparation method of Example 1 was repeated according to the above formula.

[0034] The ceramic samples prepared in Example 3 were subjected to X-ray diffraction analysis and the results are shown in the attached Figure 1c It can be seen from the figure that the ceramic of Example 3 obtained has no impurity phase.

[0035] The sintered surface of the ceramic sample prepared in Example 3 was analyzed by scanning electron microscopy, and the obtained surface morphology is shown in the attached Figure 2 , it can be seen from the figure that the ceramic surface is dense.

[0036] The surface of the ceramic sample prepared in Example 3 was ground, thinned, and gold-sprayed, and then the ferroelectric performance was tested using a ferroelectric tester. The test frequency was 2 Hz, and the maximum electric field applied was 400 kV / cm. The typical hysteresis loop measured at room temperature is shown in the attached figure. Figure 3c .

[0037] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A hybrid unconventional ferroelectric ceramic material having a layered perovskite structure, characterized in that: The chemical formula of the ceramic material is Sr 1+x Ln 2-x Sc2O7, where Ln is one or more of Sm, Nd, Eu, 0 <x<0.2。 2. The hybrid unconventional ferroelectric ceramic material having a layered perovskite structure according to claim 1, characterized in that: The ceramic material is preferably a strontium-neodymium scandate-based ferroelectric ceramic material Sr 1.05 Nd 1.95 Sc2O7, SrSrScanate based ferroelectric ceramic materials 1.1 Sm 1.9 Sc2O7, Sr(III)-E(III)-Scandate-based ferroelectric ceramic materials 1.15 Eu 1.85 Sc2O7.

3. The hybrid unconventional ferroelectric ceramic material having a layered perovskite structure according to claim 1, characterized in that: The ceramic material has a Sr 1.05 Nd 1.95 The residual ferroelectric polarization value of Sc2O7 ceramics measured is 0.9~1.1μC / cm 2 , Sr. 1.1 Sm 1.9 The residual ferroelectric polarization value of Sc2O7 ceramics measured is 2~3μC / cm 2 , Sr. 1.15 Eu 1.85 The residual ferroelectric polarization value of Sc2O7 ceramics measured is 0.5~0.75μC / cm 2 .

4. A method for preparing a hybrid unconventional ferroelectric ceramic material having a layered perovskite structure as claimed in claim 2, characterized in that: The following steps are involved: (1) The raw materials SrCO3, Nd2O3, Sm2O3, Eu2O3 and Sc2O3 were respectively prepared according to the chemical formula Sr 1.05 Nd 1.95 Sc2O7、Sr 1.1 Sm 1.9 Sc2O7、Sr 1.15 Eu 1.85 Sc2O7 ingredients, ball milled, dried and sieved; (2) calcining the powder obtained in step (1), ball-milling it for a second time, drying it and sieving it; (3) Adding a binder to the powder obtained in step (2) to form a tablet, and then sintering the tablet to obtain the ceramic material.

5. The preparation method according to claim 4, characterized in that: In step (1), the ball milling method is wet ball milling, anhydrous ethanol is used as the ball milling medium, the mass ratio of the material, the grinding ball and the anhydrous ethanol is 1:2: (0.5-1.5), and the ball milling time is 12-36 hours.

6. The preparation method according to claim 4, characterized in that: In step (2), the calcination temperature is 900-1100° C. and the calcination time is 3-9 hours.

7. The preparation method according to claim 4, characterized in that: In step (3), the adhesive is a polyvinyl alcohol aqueous solution with a concentration of 8wt%, the added amount is 5-15% of the mass of the ceramic powder, the plastic discharge temperature is 500-800°C, and the time is 1-3 hours.

8. The preparation method according to claim 4, characterized in that: In step (3), the sintering temperature is 1450°C to 1550°C, the time is 3 to 12 hours, and the heating rate is 5 to 10°C / min.

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