Ferroelectric material

Abstract

The ferroelectric material has both a crystallographic ferrochiral order and a ferroaxial order or has both a crystallographic antiferrochiral order and an antiferroaxial order.

Description

ferroelectric materials

[0001] The present disclosure relates to ferroelectric materials.

[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).

[0003] JP 2004-210601 A JP 2023-10186 A

[0004] 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. Kimura, Goto, Shintani, Ishizaka, Arima, Tokura, “Magnetic control of ferroelectric polarization”, Nature 2003, 426, 55-58.

[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.

[0007] [1] A ferroelectric material having both crystallographic ferrochiral order and ferroaxial order, or both crystallographic antiferrochiral order and antiferroaxial order. [2] A ferroelectric material having a crystallographic space group of 2 at 573K. １Spiral 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 [3] The ferroelectric material according to [1], which has both a crystallographic antiferrochiral order and an antiferroaxial order, and is represented by the general formula Sr １－ｘ－ｙ Ba ｘ Pb ｙ M ２ V ２ O ８ [4] The ferroelectric material according to [1] or [2], wherein M is at least one metal element selected from Co, Ni, Mg, and Mn, and 0≦x+y≦1. [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. [5] A ferroelectric material according to [3], wherein M has both crystallographic ferrochiral order and ferroaxial order, and is represented by the general formula LnBSiO ５ and 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. [6] The ferroelectric material according to [5], wherein Ln is at least one lanthanoid element selected from Pm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

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

[0009] Figure 1(a) and Figure 1(b) show Sr １－ｘ Ba ｘ Ni ２ V ２ O ８ 2(a), 2(b), 2(c), and 2(d) are graphs showing the results of powder neutron diffraction measurements of Sr (x=0). １－ｘ Ba ｘ Ni ２ V ２ O ８ 3(a) and 3(b) are diagrams showing the crystal structure of Sr １－ｘ Ba ｘ Ni ２ V ２ O ８ 4(a) is a graph showing the temperature change of the lattice constant of Sr (x=0). １－ｘ Ba ｘ Ni ２ V ２ O ８ 4(b) is a graph showing the temperature dependence of the dielectric constant of Sr １－ｘ Ba ｘ Mg ２ V ２ O ８ 4(c) is a graph showing the temperature dependence of the dielectric constant of Sr １－ｘ Ba ｘ Co ２ V ２ O ８ 5 is a graph showing the temperature dependence of the dielectric constant of Sr １－ｘ Ba ｘ M ２ V ２ O ８ 1 is a graph showing the x dependence of the ferroelectric phase transition temperature of the system.

[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 having both crystallographic antiferrochiral order and antiferroaxial order include, for example, ferroelectric materials having the general formula Sr １－ｘ－ｙ Ba ｘ Pb ｙ M ２ V ２ O ８ 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] When M is Co, 0≦x<1 and 0<y<1 may be satisfied. 0<x<1 and y=0 may be satisfied. 0<x≦0.5 and y=0 may be satisfied. When M is Ni, 0≦x<1 and 0<y<1 may be satisfied. 0<x<0.3 and y=0 may be satisfied. 0<x≦0.25 and y=0 may be satisfied. When M is Mg, 0≦x<1 and 0<y<1 may be satisfied. 0<x<0.85 and y=0 may be satisfied. 0<x≦0.5 and y=0 may be satisfied. When M is Mn, 0≦x<1 and 0<y<1 may be satisfied. 0<x<1 and 0≦y≦1 may be satisfied.

[0015] As a ferroelectric material having both crystallographic ferrochiral order and ferroaxial order, for example, a ferroelectric material having the general formula LnBSiO ５Examples of materials include those represented by the formula: 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 are 15 elements with atomic numbers from 57 to 71, i.e., 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, and Gd is used as Ln.

[0016] The ferroelectric material according to this embodiment has a crystal space group of 2 at 573K. 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 For example, the general formula Sr １－ｘ－ｙ Ba ｘ Pb ｙ M ２ V ２ O ８ The material represented by the formula (1) is in the crystalline space group 4 at 573K. １ Contains a spiral chain. General formula: LnBSiO ５ The material represented by the space group P3 １ Since the ferroelectric phase belongs to the crystal space group 3 at 573K, １ Includes spiral manipulation.

[0017] The ferroelectric material according to this embodiment may be single crystal or polycrystalline. The ferroelectric material according to this embodiment may be used in the form of, for example, 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, for example, a Curie point above 300 K and exhibit ferroelectricity in an actual use environment such as room temperature.

[0018] Ferroelectric materials with both crystallographic antiferrochiral and antiferroaxial order are compounds of the general formula Sr １－ｘ－ｙ Ba ｘ Pb ｙ M ２ V ２ O ８ When a material represented by the formula (I) is used, M may be Co or Mg. In this case, the Curie point becomes high.

[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.

[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) SrCO ３ (99.9%), BaCO ３ (99.95%), NiO (99.97%), MgO (99.9%), CoO (99.7%), and V２ O ５ (99.9%) starting powder was used to prepare Sr １－ｘ Ba ｘ M ２ V ２ O ８ Polycrystalline samples of (M = Ni, Mg, Co) (0 ≤ x ≤ 0.6) were synthesized. The thoroughly ground stoichiometric mixtures were sintered in air for 12 hours at 1173 K when M was Ni or Mg, and 1073 K when M was Co. The sintered powders were reground, pressed into pellets, and sintered in air for 12 hours at 1203 K when M was Ni or Mg, and 1103 K when M was Co. The resulting 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 Ni ２ V ２ O ８ The change in the crystal structure was measured by powder neutron diffraction (NPD) using a polycrystalline sample (powder sample) with (x = 0). The NPD measurements were carried out 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 carried out at temperatures from 300 K to approximately 1100 K. Rietveld refinement analysis was carried out using Z-Rietveld software.

[0025] Figure 1(a) and Figure 1(b) show Sr １－ｘ Ba ｘ M ２ V ２ O ８ 1(a) and 1(b) are graphs showing the results of powder neutron diffraction measurements of (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 Fig. 1(a) and Fig. 1(b), the horizontal axis represents the lattice spacing d, and the vertical axis represents the intensity.

[0026] 2(a), 2(b), 2(c), and 2(d) show the results of Sr １－ｘ Baｘ Ni ２ V ２ O ８ 2(a) shows the crystal structure when viewed from the c-axis direction. FIG. 2(b) shows the crystal structure when viewed from the a-axis direction. For simplicity, V atoms and O atoms are omitted from FIG. 2(b). The crystal structures in FIG. 2(a) and FIG. 2(b) show the I4 １ It has the pattern of the cd structural model.

[0027] FIG. 2(c) is a diagram showing the crystal structure as viewed from the c-axis direction. FIG. 2(d) is a diagram showing the crystal structure as viewed from the a-axis direction. For simplicity, V atoms and O atoms are omitted from FIG. 2(d). The crystal structures in FIG. 2(c) and FIG. 2(d) are I4 atoms, which exhibit paramagnetism. １ 2(a), 2(b), 2(c), and 2(d), the atomic displacements are shown enlarged by three times for clarity.

[0028] The measurement results at 573 K in Fig. 1(a) show the ferroelectricity I4 １ The pattern of the cd structure model fits well. The measurement results at 773 K in Fig. 1(b) show the paramagnetic I4 １ / acd structural model fitted well.

[0029] Figures 3(a) and 3(b) show the Sr ions obtained from the Rietveld refinement of the collected NPD patterns. １－ｘ Ba ｘ Ni ２ V ２ O ８ 3A and 3B are graphs showing the temperature change of the lattice constant a and c, respectively, for (x=0).

[0030] As shown in Figures 3(a) and 3(b), the lattice constants a and c increased monotonically with increasing temperature. An anomaly was observed in the temperature dependence of the lattice constant c at approximately 685 K. 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 Figs. 2(c) and 2(d)). These displacement patterns of the helical chains are in good agreement with the lattice parameter changes in Figs. 3(a) and 3(b), and are consistent with the SrNi alloy. ２ V ２ O ８ It was shown that the ferroelectric structure was generated by the combination of the structural chirality and the axial vector in the ferroelectric phase.

[0032] (Example 2) Sr １－ｘ Ba ｘ Mg ２ V ２ O ８ All the steps were the same as in Example 1 except that a polycrystalline sample (x = 0) was used. ２＋ Unlike non-magnetic Mg, which does not have d electrons ２＋ Ion-incorporated SrMg ２ V ２ O ８ A similar ferroelectric phase transition (Tc=930K) was observed for .

[0033] (Example 3) Sr １－ｘ Ba ｘ Co ２ V ２ O ８ All the steps were the same as in Example 1 except that a polycrystalline sample (x = 0) was used. ２＋ Co, which has the same number of d electrons as ２＋ Ion-incorporated SrCo ２ V ２ O８ A similar ferroelectric phase transition (Tc=920K) was observed for .

[0034] Example 4: Sr alloys with different Ba contents (i.e., different x values) １－ｘ Ba ｘ M ２ V ２ O ８ The 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 samples 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] FIG. 4(a) shows Sr １－ｘ Ba ｘ Ni ２ V ２ O ８ 4(a) shows the temperature dependence of the dielectric constant of Sr １－ｘ Ba ｘ Mg ２ V ２ O ８ 4(b) shows the temperature dependence of the dielectric constant of Sr. １－ｘ Ba ｘ Co ２ V ２ O ８ 4(c) is a graph showing the temperature dependence of the dielectric constant of the dielectric constant of the dielectric film when 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') shows a peak at temperatures below 300 K. The peak temperature of the dielectric constant is independent of frequency. These results indicate a ferroelectric phase transition below 300 K.

[0037] FIG. １－ｘ Baｘ M ２ V ２ O ８ 1 is a graph showing the x dependence of the ferroelectric phase transition temperature of the system determined by NPD measurement and dielectric constant measurement. Data at x=0 is determined by NPD measurement, and the other data is 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 M ２ V ２ O ８ The relationship between Tc and x in the system has a constant slope regardless of the elements that make up the helical chain (screw 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 Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Build resilient infrastructure, promote inclusive and sustainable industrialization, innovate and foster innovation."

Claims

1. Ferroelectric materials that have both ferrochiral and ferroaxial crystallographic order, or both antiferrochiral and antiferroaxial crystallographic order.

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 The ferroelectric material of claim 1 , comprising any one of a spiral operation.

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

4. The ferroelectric material according to claim 3, wherein 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.

5. It has both crystallographic ferrochiral and ferroaxial order and has the general formula LnBSiO ５ 3. The ferroelectric material according to claim 1, wherein 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.

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

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