Ferroelectric material

Abstract

To provide a new ferroelectric material exhibiting ferroelectricity by a new mechanism.SOLUTION: The ferroelectric material has a combination of crystallographic ferrochiral and ferroaxial order, or a combination of crystallographic antiferrochiral and antiferroaxial order.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to ferroelectric materials. [Background technology]

[0002] In recent years, the use and development of ferroelectric materials has been actively pursued. Ferroelectric materials that have been reported so far include displacement-type ferroelectric materials due to the Jahn-Teller effect (Patent Document 1, Patent Document 2, and Non-Patent Document 1) and magnetically ordered ferroelectric materials (Non-Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-210601 [Patent Document 2] Japanese Patent Publication No. 2023-10186 [Non-patent literature]

[0004] [Non-Patent Document 1] Seshadri, Hill, “Visualizing the Role of Bi 6s “Lone Pairs” in the Off-Center Distortion in Ferromagnetic BiMnO3”, Chem. Mater. 2001, 13, 9, 2892‐2899. [Non-patent document 2] Kimura, Goto, Shintani, Ishizaka, Arima, Tokura, “Magnetic control of ferroelectric polarization”, Nature 2003, 426, 55-58. Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of the above-mentioned displacive ferroelectric materials, the manifestation of ferroelectricity is accompanied by distortion of the crystal lattice. As a result, lattice defects often occur with repeated use, posing a problem in device reliability. In the case of magnetically ordered ferroelectric materials, the ferroelectric polarization is small, which means that when used in memory devices, the polarization is small and readability is an issue. Therefore, there has been a demand for new materials that exhibit ferroelectricity through a new mechanism other than the displacive or magnetically ordered types.

[0006] An object of the present disclosure is to provide a new ferroelectric material that exhibits ferroelectricity through a new mechanism. [Means for solving the problem]

[0007] [1] A combination of crystallographic ferrochiral and ferroaxial order, or a combination of crystallographic antiferrochiral and antiferroaxial order, Ferroelectric materials. [2] The crystal space group at 573K contains any one of 21 helical operations, 31 helical operations, 32 helical operations, 41 helical operations, 42 helical operations, 43 helical operations, 61 helical operations, 62 helical operations, 63 helical operations, 64 helical operations, and 65 helical operations. [1] The ferroelectric material according to [1]. [3] It has both crystallographic antiferrochiral and antiferroaxial order, General formula Sr 1-x-y Ba x Pb y It is represented by M2V2O8, M is at least one metal element selected from Co, Ni, Mg, and Mn; 0≦x+y≦1, The ferroelectric material according to [1] or [2]. [4] If M is Co, then 0≦x<1 and 0 <y<1であるか、0<x<1、かつ、y=0であり、 When M is Ni, 0≦x<1 and 0 <y<1であるか、0<x<0.3、かつ、y=0であり、 When M is Mg, 0≦x<1 and 0 <y<1であるか、0<x<0.85、かつ、y=0であり、 If M is Mn, then 0≦x<1 and 0 <y<1であるか、0<x<1、かつ、0≦y≦1である、 [3] The ferroelectric material according to [3]. [5] It has both crystallographic ferrochiral and ferroaxial order, It is represented by the general formula LnBSiO5, Ln is at least one lanthanide element selected from La, Nd, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; The ferroelectric material according to [1] or [2]. [6] Ln is at least one lanthanide element selected from Pm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; [5] The ferroelectric material according to [5]. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, a new ferroelectric material is provided that exhibits ferroelectricity via a new mechanism. [Brief explanation of the drawings]

[0009] [Figure 1] 1(a) and 1(b) are graphs showing the results of powder neutron diffraction measurements of Sr1-xBaxNi2V2O8 (x=0). [Figure 2] 2(a), 2(b), 2(c), and 2(d) are diagrams showing the crystal structure of Sr1-xBaxNi2V2O8 (x=0). [Figure 3] 3(a) and 3(b) are graphs showing the temperature dependence of the lattice constant of Sr1-xBaxNi2V2O8 (x=0). [Figure 4]Figure 4(a) shows the temperature dependence of the dielectric constant of Sr1-xBaxNi2V2O8, Figure 4(b) shows the temperature dependence of the dielectric constant of Sr1-xBaxMg2V2O8, and Figure 4(c) shows the temperature dependence of the dielectric constant of Sr1-xBaxCo2V2O8. [Figure 5] FIG. 5 is a graph showing the x dependence of the ferroelectric phase transition temperature of the Sr1-xBaxM2V2O8 system. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0011] The ferroelectric material according to this embodiment is a material having both crystallographic ferrochiral order and ferroaxial order, or a material having both antiferrochiral order and antiferroaxial order.

[0012] Crystallographic chiral order refers to a state in which chirality (left-right asymmetry) is regularly arranged in the crystals of a substance. Crystallographic ferrochiral order refers to a state in which chirality is arranged in the same direction. Crystallographic antiferrochiral order refers to a state in which chirality is arranged in alternating opposite directions. Crystallographic axial order refers to a state in which axiality (left-right rotational asymmetry) is regularly arranged in the crystals of a substance. Crystallographic ferroaxial order refers to a state in which axiality is arranged in the same direction. Crystallographic antiferroaxial order refers to a state in which axiality is arranged in alternating opposite directions.

[0013] Ferroelectric materials that have both crystallographic antiferrochiral and antiferroaxial order include those with the general formula Sr 1-x-y Ba x Pb yExamples of such materials include those represented by M2V2O8. In this general formula, M is at least one metal element selected from Co, Ni, Mg, and Mn. 0≦x+y≦1. x may satisfy 0≦x≦1, and y may satisfy 0≦y≦1.

[0014] If M is Co, then 0≦x<1 and 0 <y<1であってもよい。0<x<1、かつ、y=0であってもよい。0<x≦0.5、かつ、y=0であってもよい。 When M is Ni, 0≦x<1 and 0 <y<1であってもよい。0<x<0.3、かつ、y=0であってもよい。0<x≦0.25、かつ、y=0であってもよい。 When M is Mg, 0≦x<1 and 0 <y<1であってもよい。0<x<0.85、かつ、y=0であってもよい。0<x≦0.5、かつ、y=0であってもよい。 If M is Mn, then 0≦x<1 and 0 <y<1であってもよい。0<x<1、かつ、0≦y≦1であってもよい。

[0015] An example of a ferroelectric material having both crystallographic ferrochiral and ferroaxial order is a material represented by the general formula LnBSiO5. In this general formula, Ln is at least one lanthanoid element selected from La, Nd, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Lanthanoid elements have atomic numbers from 57 to 71, i.e., the 15 elements from lanthanum to lutetium. Ln may be at least one lanthanoid element selected from Pm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In this case, a lanthanoid element other than La, Ce, Pr, Nd, Sm, or Gd is used as Ln.

[0016] The ferroelectric material according to this embodiment has a crystal space group at 573 K that includes any one of 21 screw interactions, 31 screw interactions, 32 screw interactions, 41 screw interactions, 42 screw interactions, 43 screw interactions, 61 screw interactions, 62 screw interactions, 63 screw interactions, 64 screw interactions, and 65 screw interactions. For example, the ferroelectric material of the general formula Sr1-x-y Ba x Pb y A material represented by M2V2O8 contains 41 screw operations in its crystal space group at 573 K. A material represented by the general formula LnBSiO5 has a ferroelectric phase belonging to the space group P31, and therefore contains 31 screw operations in its crystal space group at 573 K.

[0017] The ferroelectric material according to this embodiment may be single crystal or polycrystalline. The ferroelectric material according to this embodiment may be used, for example, in the form of a bulk, a thin film, particles, or fibers. The ferroelectric material according to this embodiment may be used in a state where a voltage equal to or greater than the coercive field is applied (poling). The ferroelectric material according to this embodiment may have a Curie point exceeding 300 K, for example, and may exhibit ferroelectricity in an actual use environment, such as room temperature.

[0018] Ferroelectric materials with both crystallographic antiferrochiral and antiferroaxial order have been developed using the general formula Sr 1-x-y Ba x Pb y When a material represented by M2V2O8 is used, M may be Co or Mg, in which case the Curie point becomes higher.

[0019] The ferroelectric material according to this embodiment may be a dielectric, a metal, or a semiconductor. In ordinary metals, the spin and momentum of electrons are unrelated, but in special metals with polarity (polar metals), a locked state is realized in which the direction of the spin is determined depending on the direction of electron motion.

[0020] The ferroelectric material according to this embodiment can be applied to various devices, such as nonvolatile memories, wavelength converters, solar cells, capacitors, infrared sensors, igniters, speakers, vibrators, filters, ultrasonic transmitters / receivers, and actuators.

[0021] The present invention is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present invention. [Example]

[0022] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0023] (Synthesis example) Starting powders of SrCO3 (99.9%), BaCO3 (99.95%), NiO (99.97%), MgO (99.9%), CoO (99.7%), and V2O5 (99.9%) were used to synthesize Sr by a solid-state reaction method. 1-x Ba x Polycrystalline samples of M2V2O8 (M = Ni, Mg, Co) (0 ≤ x ≤ 0.6) were synthesized. The thoroughly ground stoichiometric mixtures were calcined in air for 12 h at 1173 K when M was Ni or Mg, and 1073 K when M was Co. The calcined powders were reground, pressed into pellets, and sintered in air for 12 h at 1203 K when M was Ni or Mg, and 1103 K when M was Co. The polycrystalline samples were confirmed to be single-phase by powder X-ray diffraction.

[0024] Example 1 Among the samples obtained in the synthesis example, Sr 1-x Ba x The crystal structure of a polycrystalline Ni2V2O8 (x = 0) powder sample was analyzed by powder neutron diffraction (NPD). The NPD measurements were performed using a high-resolution powder diffractometer (BL08, SuperHRPD) at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The polycrystalline sample was placed in a V-Ni cell, and measurements were performed at temperatures from 300 K to approximately 1100 K. Rietveld refinement analysis was performed using the Z-Rietveld software.

[0025] Figure 1(a) and Figure 1(b) show the Sr 1-x Ba x1(a) and 1(b) are graphs showing the results of powder neutron diffraction measurements of M2V2O8 (M=Ni) (x=0). FIG. 1(a) is a graph showing the results of measurements at 573 K. FIG. 1(b) is a graph showing the results of measurements at 773 K. In FIGS. 1(a) and 1(b), the horizontal axis represents the lattice spacing d, and the vertical axis represents the intensity.

[0026] Figures 2(a), 2(b), 2(c), and 2(d) show the Sr 1-x Ba x 2(a) and 2(b) are diagrams showing the crystal structure of Ni2V2O8 (x=0). FIG. 2(a) shows the crystal structure as viewed from the c-axis direction. FIG. 2(b) shows the crystal structure as viewed from the a-axis direction. For simplicity, V and O atoms are omitted from FIG. 2(b). The crystal structures in FIG. 2(a) and 2(b) have the I41cd structure model pattern, which indicates ferroelectricity.

[0027] Figure 2(c) shows the crystal structure as viewed from the c-axis direction. Figure 2(d) shows the crystal structure as viewed from the a-axis direction. For simplicity, V and O atoms are omitted from Figure 2(d). The crystal structures in Figures 2(c) and 2(d) have the I41 / acd structure model pattern, which indicates paramagnetism. In Figures 2(a), 2(b), 2(c), and 2(d), the atomic displacements are shown enlarged three times for clarity.

[0028] The measurement results at 573 K in Figure 1(a) fit well with the I41cd structure model pattern, which indicates ferroelectricity, in Figure 2(b). The measurement results at 773 K in Figure 1(b) fit well with the I41 / acd structure model, which indicates paramagnetism, in Figure 2(d).

[0029] Figures 3(a) and 3(b) show the Sr concentration distribution obtained from the Rietveld refinement of the collected NPD patterns. 1-x Ba x 3A and 3B are graphs showing the temperature dependence of the lattice constant a and c, respectively, of Ni2V2O8 (x=0).

[0030] As shown in Figures 3(a) and 3(b), the lattice constants a and c increased monotonically with increasing temperature. At approximately 685 K, an anomaly was observed in the temperature dependence of the lattice constant c. This lattice anomaly is due to the ferroelectric phase transition. The ferroelectric phase transition temperature Tc is approximately 685 K (Tc ~ 685 K). In other words, Figures 2(a) and 2(b) show the crystal structure at a temperature (573 K) lower than the ferroelectric phase transition temperature Tc. Figures 2(c) and 2(d) show the crystal structure at a temperature (773 K) higher than the ferroelectric phase transition temperature Tc.

[0031] In the low-temperature phase, adjacent helical chains alternately rotate in opposite directions (see Fig. 2(a)), accompanied by uniform translational motion parallel to the c-axis, resulting in rotational distortion (see Fig. 2(b)). Conversely, in the high-temperature phase, the rotational distortion and translational displacement simultaneously disappear (see Fig. 2(c) and Fig. 2(d)). These displacement patterns of the helical chains are in good agreement with the changes in the lattice constants in Fig. 3(a) and Fig. 3(b), indicating that the ferroelectric structure emerges through the combination of the structural chirality and axial vector in SrNi2V2O8.

[0032] Example 2 Sr 1-x Ba x All the procedures were the same as in Example 1, except that a polycrystalline sample of Mg2V2O8 (x = 0) was used. 2+ Unlike non-magnetic Mg, which does not have d electrons 2+ A similar ferroelectric phase transition (Tc=930K) was also observed for SrMg2V2O8 incorporating ions.

[0033] Example 3 Sr 1-x Ba x All the procedures were the same as in Example 1, except that a polycrystalline sample of Co2V2O8 (x = 0) was used. 2+ Co has the same number of d electrons as 2+ A similar ferroelectric phase transition (Tc=920K) was also observed for SrCo2V2O8 incorporating ions.

[0034] Example 4 Sr with different Ba contents (i.e., different values ​​of x)1-x Ba x The M2V2O8 system was synthesized and its dielectric properties were measured. For dielectric constant measurements, pellet samples were polished to a thickness of approximately 500 μm. Silver paste was applied to both sides of the polished pellet sample and used as electrodes. The dielectric constant and pyroelectric current were measured using an LCR meter (Agilent E4980A) and an electrometer (Keithley Model 6517A), respectively. The dielectric constant was measured by applying an AC voltage of 10 kHz to the sample.

[0035] Figure 4(a) shows the Sr 1-x Ba x 4(a) shows the temperature dependence of the dielectric constant of Ni2V2O8. The cases of x=0.2, 0.25, 0.3, 0.35, and 0.4 are shown in Fig. 4(a). Fig. 4(b) shows the temperature dependence of the dielectric constant of Sr 1-x Ba x 4(b) shows the temperature dependence of the dielectric constant of Mg2V2O8 for x = 0.4, 0.45, and 0.5. FIG. 4(c) shows the temperature dependence of the dielectric constant of Sr 1-x Ba x 4(c) is a graph showing the temperature dependence of the dielectric constant of Co2V2O8, where x = 0.5, 0.53, and 0.56.

[0036] In all of the Ba-substituted samples shown in Figures 4(a), 4(b), and 4(c), the real part of the dielectric constant (ε') peaks at temperatures below 300 K. The dielectric constant peak temperature is independent of frequency. These results indicate a ferroelectric phase transition below 300 K.

[0037] Figure 5 shows the Sr 1-x Ba x 1 is a graph showing the x dependence of the ferroelectric phase transition temperature of the M2V2O8 system determined by NPD measurement and dielectric constant measurement. Data at x=0 are determined by NPD measurement, and the other data are determined by dielectric constant measurement.

[0038] As shown in Figure 5, Tc decreases linearly with increasing x, whether M is Ni, Mg, or Co. In particular, the Tc obtained by NPD at x = 0 is in perfect agreement with the value linearly extrapolated from the data points of the dielectric measurements. This confirms that the dielectric anomaly is a direct result of the ferroelectric phase transition. Interestingly, in the case of Sr 1-x Ba x The relationship between Tc and x in the M2V2O8 system has a constant slope regardless of the elements that make up the helical chain, which supports the idea that ferroelectricity is manifested by the combination of antiferrochiral and antiferroaxial order, regardless of the components.

[0039] [Additional remarks] The ferroelectric material disclosed herein exhibits ferroelectricity through a new mechanism and can improve device reliability, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Industry, innovation and infrastructure"

Claims

1. A combination of crystallographic ferrochiral and ferroaxial order, or a combination of crystallographic antiferrochiral and antiferroaxial order, Ferroelectric materials.

2. At 573K, the crystal space group is 2 １ Spiral operation, 3 １ Spiral operation, 3 ２ Spiral operation, 4 １ Spiral operation, 4 ２ Spiral operation, 4 ３ Spiral operation, 6 １ Spiral operation, 6 ２ Spiral operation, 6 ３ Spiral operation, 6 ４ Spiral operation, and 6 ５ including one of the spiral operations, The ferroelectric material of claim 1 .

3. It has both crystallographic antiferrochiral and antiferroaxial order, General formula Sr １－ｘ－ｙ Ba ｘ Pb ｙ M ２ V ２ O ８ is expressed as M is at least one metal element selected from Co, Ni, Mg, and Mn; 0≦x+y≦1, The ferroelectric material according to claim 1 or 2.

4. When M is Co, 0≦x<1 and 0<y<1, or 0<x<1 and y=0; When M is Ni, 0≦x<1 and 0<y<1, or 0<x<0.3 and y=0; when M is Mg, 0≦x<1 and 0<y<1, or 0<x<0.85 and y=0; When M is Mn, 0≦x<1 and 0<y<1, or 0<x<1 and 0≦y≦1. The ferroelectric material of claim 3 .

5. It has both crystallographic ferrochiral and ferroaxial order, General formula LnBSiO ５ is expressed as Ln is at least one lanthanoid element selected from La, Nd, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; The ferroelectric material according to claim 1 or 2.

6. Ln is at least one lanthanoid element selected from Pm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; The ferroelectric material according to claim 5 .

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