Ferroelectric perovskite type rbnbo3 and method for manufacturing same

Abstract

Provided are: a ferroelectric perovskite type RbNbO3 which has a high relative dielectric constant; and a method for manufacturing the same. A ferroelectric perovskite type RbNbO3 according to the present invention is characterized by having a relative dielectric constant of 500 or more at 23°C. A method for manufacturing a ferroelectric perovskite type RbNbO3 according to the present invention includes a sintering step for subjecting RbNbO3 in an atmospheric pressure phase to a heat treatment at a temperature T1 of 650°C or higher at a pressure of 3 GPa or higher. It is preferable for the method to include, after the sintering process, a cooling step for lowering the temperature of the obtained sintered material from the temperature T1 to a temperature T2 that is 100°C or lower at a rate of 200°C / second or more at atmospheric pressure.

Description

Ferroelectric perovskite-type RbNbO3 and method for manufacturing the same

[0001] This invention relates to a ferroelectric perovskite-type RbNboO with a high dielectric constant. ３ And the method of manufacturing the same.

[0002] For example, there is active development of multilayer ceramic capacitors that achieve high capacity and reliability, and electronic devices equipped with them, which have a structure in which a pair of external electrodes are arranged alternately on both end faces of a capacitor element in which an internal electrode layer is stacked via a dielectric ceramic layer, so as to be electrically connected to the internal electrode layer exposed on the opposite end face. Conventionally, barium titanate perovskite (BaTiO) has been used as the material for forming the dielectric layer. ３ Dielectric compositions containing compounds in which some of Ba and Ti are substituted with other atoms (Ca, Sr, Mg, rare earth elements, etc.) have been used.

[0003] General formula ABO ３ As a method for producing a composite oxide powder having a perovskite-type structure as shown, for example, Patent Document 1 discloses a method for producing a composite oxide powder characterized by including a dissolution generation step of heating a hydroxide of an element constituting the A-site component (barium hydroxide) containing crystal water to produce a dissolution containing the A-site component, and a reaction step of reacting an oxide powder of an element constituting the B-site component, which consists of predetermined ultrafine particles (titanium dioxide), with the dissolution to produce a reaction compound.

[0004] Also, the general formula ABO ３ Patent Document 2 describes a method for producing a perovskite-type composite oxide represented by (A containing at least Ba and Ca, and B containing at least Ti), which involves reacting at least titanium dioxide, calcium carbonate, and barium hydroxide in a slurry liquid (Ba １－ｘ Ca ｘ ) ｍ TiO ３ A method for producing a perovskite-type composite oxide is disclosed, characterized by including a reaction step that generates a perovskite-type composite oxide represented by (0 < x ≤ 0.125).

[0005] Furthermore, as a complex oxide having a perovskite structure, RbNbO ３ is known (Non-Patent Document 1).

[0006] JP 2003-252623, JP 2012-176857

[0007] Masayuki Fukuda, et. Al, Journal of the Ceramic Society of Japan 131[5] 126-129 (2023)

[0008] An object of the present invention is to provide a ferroelectric perovskite-type RbNbO having a high relative permittivity ３ and a method for producing the same.

[0009] The present invention is as follows. 1. A ferroelectric perovskite-type RbNbO characterized in that the relative permittivity at 23°C is 500 or more ３ . 2. A method for producing the ferroelectric perovskite-type RbNbO according to Item 1 above, comprising a sintering step of heat-treating the RbNbO in the normal pressure phase ３ at a pressure of 3 GPa or more and a temperature T1 of 650°C or more. A method for producing a ferroelectric perovskite-type RbNbO ３ characterized by the above. 3. Further, the ferroelectric perovskite-type RbNbO according to Item 2 above, comprising a cooling step of cooling the sintered product obtained in the sintering step from the temperature T1 to a temperature T2 of 100°C or less at a rate of 200°C / second or more under atmospheric pressure ３ . A method for producing RbNbO ３ of a ferroelectric perovskite type.

[0010] The ferroelectric perovskite-type RbNbO of the present invention ３ has a high relative permittivity of 500 or more at 23°C, and high performance is expected in electronic components (multilayer ceramic capacitors, thin film capacitors, piezoelectric elements, capacitors, etc.) provided with a layer formed using this ferroelectric perovskite-type RbNbO ３ . Further, the ferroelectric perovskite-type RbNbO of the present invention ３According to the manufacturing method, in the sintering process, for example, by using a cubic anvil type high-pressure generator, a ferroelectric perovskite type RbNbO with a relative permittivity of 500 or more at 23°C is produced. ３ It can be manufactured efficiently.

[0011] Perovskite-type RbNboO obtained in Example 1 ３ This is an electron microscope image of the perovskite-type RbNboO obtained in Example 1. ３ This is a powder X-ray diffraction pattern. Perovskite-type RbNbO obtained in Example 1 ３ This is a graph showing the relative permittivity.

[0012] The present invention provides a ferroelectric perovskite-type RbNbo ３ The dielectric constant at 23°C is 500 or higher, preferably 600 or higher, and more preferably 700 or higher. The dielectric constant can be measured by the method described in [Examples].

[0013] The present invention provides a ferroelectric perovskite-type RbNbo ３ The material is a cubic crystal, and may be either a single crystal or a polycrystalline material. The powder X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays is shown in Figure 2, for example, and has diffraction peaks at least at 2θ = 31.1 ± 0.1 deg, 43.8 ± 0.15 deg, 45.4 ± 0.15 deg, and 64.9 ± 0.2 deg. Furthermore, its crystal structure is an orthorhombic crystal with space group Amm2 symmetry, and its lattice constants are a = 3.9937 (2) Å, b = 5.8217 (3) Å, and c = 5.8647 (2) Å.

[0014] Ferroelectric perovskite-type RbNboO in the present invention ３ The manufacturing method involves producing an atmospheric pressure phase RbNbO that is stable at atmospheric pressure, has the same chemical composition but a different crystal structure, and is not a ferroelectric. ３ Preferably, the process includes a sintering step in which the material is heat-treated at a pressure of 3 GPa or higher and a temperature T1 of 650°C or higher, and after this sintering step, a cooling step is further provided in which the obtained sintered material is cooled from the above temperature T1 to a temperature T2 of 100°C or lower at a rate of 200°C / second or higher under atmospheric pressure.

[0015] RbNboO, the atmospheric pressure phase used in the sintering process ３ This can be obtained by conventionally known methods. In the present invention, this atmospheric pressure phase RbNbO ３ The material is subjected to heat treatment at high temperature under high pressure conditions. The pressure is 3 GPa or higher, preferably 3.5 GPa or higher, and more preferably 4 GPa or higher. Such high pressure can be generated by a high-pressure generator such as a multi-anvil type including a cubic anvil type, or a belt type. The heat treatment temperature T1 is 650°C or higher, preferably 700°C or higher, and more preferably 900°C or higher. The upper limit is 1100°C. The heat treatment in the sintering process may be performed while keeping the temperature T1 constant, or while increasing the temperature to satisfy 650°C or higher.

[0016] Atmospheric pressure phase RbNbO in the sintering process ３ The heat treatment time is usually between 10 and 60 minutes, but is not particularly limited and is set as appropriate to control the structure, particle shape, etc.

[0017] In the present invention, after heat treatment in the sintering process, the product (sintered material) is returned to room temperature and atmospheric pressure, thereby producing a ferroelectric perovskite-type RbNbO with a high dielectric constant. ３ This can be achieved. Furthermore, the present invention preferably includes a cooling step in which the product (sintered material) is cooled from temperature T1 to a temperature T2 of 100°C or less at a rate of 200°C / second or more, at atmospheric pressure, rather than being allowed to cool naturally from temperature T1 over time. Temperature T2 is preferably 80°C or less, more preferably 50°C or less. The cooling rate is 200°C / second or more, preferably 250°C / second or more. The upper limit is usually 300°C / second.

[0018] Ferroelectric perovskite-type RbNboO obtained by the manufacturing method of the present invention ３ Because it is highly stable in the atmosphere and at room temperature (23°C to 25°C), it is easy to handle, and is a ferroelectric perovskite type RbNbO ３ It is suitable for manufacturing products such as electronic components (multilayer ceramic capacitors, thin-film capacitors, piezoelectric elements, capacitors, etc.) that have a layer containing this material.

[0019] The embodiments of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way to these examples.

[0020] Example 1: Rb with a purity of 99% that has been preheated to 300°C in air to remove adhering moisture. ２ CO ３ Powder and 99.99% pure Nb ２ O ５ The powders were weighed and mixed in a glove box, based on a molar ratio of 1:1, with an excess of 1-5% Rb elements relative to Nb elements. The resulting mixed powder was then heated (sintered) in a box-type electric furnace in air at 800°C for 10 hours to obtain the atmospheric pressure phase RbNbO ３ The atmospheric pressure phase RbNboO was obtained. ３ It was stored in the glove compartment. Next, in the glove compartment, approximately 0.5 grams of atmospheric pressure phase RbNbO ３ The material was packed into a gold cell and heat-treated for 12 minutes at a temperature of 950°C and a pressure of 4 GPa using a cubic anvil type high-temperature, high-pressure synthesis apparatus. Afterward, it was cooled to 900°C over 1 hour, and then rapidly cooled to room temperature (cooling rate of 200°C / second) to obtain cubic crystals. Figure 1 shows an image taken with a JEOL scanning electron microscope "JED-6000" (product name). Furthermore, an X-ray diffraction pattern of this crystal was obtained using a Rigaku X-ray diffractometer "SmartLAB" (product name) using Cu-Kα rays, and Figure 2 shows that it is a perovskite type RbNbO ３ It was found that... Then, through analysis using the Rietveld method and single-crystal X-ray diffraction patterns, the perovskite-type RbNbO was obtained. ３ It was found to be an orthorhombic crystal with symmetry of space group Amm2, and its lattice constants were a = 3.9937(2) Å, b = 5.8217(3) Å, and c = 5.8647(2) Å.

[0021] Furthermore, perovskite-type RbNboO ３ The relative permittivity of the crystal was measured at a temperature of 23°C and a frequency range of 0.01 to 1,000,000 Hz using an LCR meter such as one manufactured by Agilent. Specifically, perovskite-type RbNbO was measured using abrasive paper. ３The crystal surface was polished, then gold for electrodes was deposited on both sides using a sputtering apparatus. Silver wires were attached to these electrodes using Dotite, and the dielectric constant was measured by connecting to an LCR meter. In the case of single crystals, the entire surface of the sample was directly covered with Dotite without polishing, and the dielectric constant was measured by attaching silver wires to it while changing the frequency, obtaining the graph in Figure 3. From Figure 3, the obtained perovskite-type RbNbO ３ This indicates that it is a ferroelectric material with a relative permittivity of 500 or more.

[0022] The present invention provides a ferroelectric perovskite-type RbNbo ３ It is suitable as a raw material for manufacturing multilayer ceramic capacitors, thin-film capacitors, piezoelectric elements, capacitors, etc.

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