Ferroelectric perovskite-type RbNbO3 and method for manufacturing the same

Abstract

This invention provides a ferroelectric perovskite-type RbNbO3 with a high dielectric constant and a method for producing the same. [Solution] The ferroelectric perovskite-type RbNbO3 of the present invention is characterized by having a relative permittivity of 500 or more at 23°C. The method for producing the ferroelectric perovskite-type RbNbO3 of the present invention comprises a sintering step in which RbNbO3 in the atmospheric pressure phase is heat-treated at a pressure of 3 GPa or more and a temperature T1 of 650°C or more. After the sintering method, it is preferable to include a cooling step in which the obtained sintered product is cooled from temperature T1 to a temperature T2 of 100°C or less at a rate of 200°C / second or more under atmospheric pressure.

Description

Technical Field

[0001] The present invention relates to a ferroelectric perovskite RbNbO3 having a high relative permittivity and a method for producing the same.

Background Art

[0002] For example, a structure in which a pair of external electrodes are disposed on both end faces of a capacitor element in which an internal electrode layer is laminated through a ceramic layer as a dielectric layer so as to be electrically connected to the internal electrode layer exposed on the opposite end faces alternately is provided. Development of multilayer ceramic capacitors that achieve large capacity and high reliability and electronic devices mounted with the same has been actively carried out. Conventionally, as a material used for forming the dielectric layer, a dielectric composition containing a perovskite-type barium titanate (BaTiO3) or a compound in which a part of Ba and Ti is substituted with other atoms (Ca, Sr, Mg, rare earth elements, etc.) has been used.

[0003] As a method for producing a composite oxide powder having a perovskite-type structure represented by the general formula ABO3, for example, Patent Document 1 discloses a solution generation step of heating a hydroxide (barium hydroxide) of an element constituting the A-site component containing crystal water to generate a solution containing the A-site component, and a reaction step of reacting an oxide powder (titanium dioxide) of an element constituting the B-site component composed of predetermined ultrafine particles with the solution to generate a reaction product. A method for producing a composite oxide powder is disclosed.

[0004] Further, as a method for producing a perovskite-type composite oxide represented by the general formula ABO3 (A includes at least Ba and Ca, and B includes at least Ti), Patent Document 2 discloses reacting at least titanium oxide, calcium carbonate, and barium hydroxide in a slurry solution to generate a perovskite-type composite oxide represented by (Ba 1-x Ca x ) m TiO3 (0 <x ≦ 0.125). A method for producing a perovskite-type composite oxide is disclosed, which includes a reaction step of generating the perovskite-type composite oxide.

[0005] Furthermore, RbNbO3 is known as a composite oxide having a perovskite-type structure (Non-Patent Literature 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-252623 [Patent Document 2] Japanese Patent Publication No. 2012-176857 [Non-patent literature]

[0007] [Non-Patent Document 1] Masayuki Fukuda, et. Al, Journal of the Ceramic Society of Japan 131[5] 126-129 (2023) [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a ferroelectric perovskite-type RbNbO3 with a high relative permittivity and a method for producing the same. [Means for solving the problem]

[0009] The present invention is shown below. A ferroelectric perovskite-type RbNbO3 characterized by having a relative permittivity of 500 or more at 1.23℃. 2. A method for producing the ferroelectric perovskite-type RbNbO3 described in item 1 above, A method for producing ferroelectric perovskite-type RbNbO3, characterized by comprising a sintering step of heat-treating RbNbO3 in an atmospheric pressure phase at a pressure of 3 GPa or higher and a temperature T1 of 650°C or higher. 3. A method for producing ferroelectric perovskite-type RbNbO3 according to item 2, further comprising a cooling step of lowering the temperature of the sintered product obtained in the above sintering step from the above temperature T1 to a temperature T2 of 100°C or less at a rate of 200°C / second or more under atmospheric pressure. [Effects of the Invention]

[0010] The ferroelectric perovskite-type RbNbO3 of the present invention has a high relative permittivity of 500 or more at 23°C, and is expected to provide high performance in electronic components (multilayer ceramic capacitors, thin-film capacitors, piezoelectric elements, capacitors, etc.) that incorporate layers formed using this ferroelectric perovskite-type RbNbO3. Furthermore, according to the method for producing ferroelectric perovskite-type RbNbO3 of the present invention, by using, for example, a cubic anvil type high-pressure generator in the sintering process, ferroelectric perovskite-type RbNbO3 having a relative permittivity of 500 or more at 23°C can be efficiently produced. [Brief explanation of the drawing]

[0011] [Figure 1] This is an electron microscope image of the perovskite-type RbNbO3 obtained in Example 1. [Figure 2] This is a powder X-ray diffraction image of the perovskite-type RbNbO3 obtained in Example 1. [Figure 3] This graph shows the relative permittivity of the perovskite-type RbNbO3 obtained in Example 1. [Modes for carrying out the invention]

[0012] The ferroelectric perovskite-type RbNbO3 of the present invention has a relative permittivity of 500 or more at 23°C, preferably 600 or more, and more preferably 700 or more. The relative permittivity can be measured by the method described in [Examples].

[0013] The ferroelectric perovskite-type RbNbO3 of the present invention is a cubic crystal, which may be either a single crystal or a polycrystal. The powder X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays is shown in, for example, FIG. 2, 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. Further, its crystal structure is an orthorhombic crystal having the symmetry of the space group Amm2, and the lattice constants are a = 3.9937(2) Å, b = 5.8217(3) Å, and c = 5.8647(2) Å.

[0014] The manufacturing method of the ferroelectric perovskite-type RbNbO3 in the present invention is stable at normal pressure, has the same chemical composition but different crystal structures, and is not a ferroelectric RbNbO3 of the normal pressure phase. It includes a sintering process of heat-treating the RbNbO3 of the normal pressure phase at a pressure of 3 GPa or more and a temperature T1 of 650 °C or more. After this sintering process, it is preferable to further include a cooling process of cooling the obtained sintered product 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.

[0015] The RbNbO3 of the normal pressure phase used in the sintering process can be obtained by a conventionally known method. In the present invention, this RbNbO3 of the normal pressure phase is heat-treated at a high temperature under high-pressure conditions. The pressure is 3 GPa or more, preferably 3.5 GPa or more, and more preferably 4 GPa or more. Such a high pressure can be generated by a multi-anvil type including a cubic anvil type and a belt type, etc., high-pressure generating devices. Also, the heat treatment temperature T1 is 650 °C or more, preferably 700 °C or more, and more preferably 900 °C or more. 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 while satisfying 650 °C or more.

[0016] The heat treatment time of the RbNbO3 of the normal pressure phase in the sintering process is usually 10 minutes or more and 60 minutes or less, but is not particularly limited, and is appropriately set for controlling the structure particle shape, etc.

[0017] In the present invention, after the heat treatment in the sintering process, by returning the product (sintered body) to normal temperature and normal pressure, a ferroelectric perovskite-type RbNbO3 having a high relative permittivity can be obtained. Incidentally, in the present invention, rather than allowing the product (sintered body) to cool naturally from temperature T1 over time, it is preferable to include a cooling step of cooling the product from temperature T1 to a temperature T2 of 100 °C or less at a rate of 200 °C / second or more as the atmospheric pressure. The temperature T2 is preferably 80 °C or less, more preferably 50 °C or less. Also, the cooling rate is 200 °C / second or more, preferably 250 °C / second or more. Incidentally, the upper limit is usually 300 °C / second.

[0018] The ferroelectric perovskite-type RbNbO3 obtained by the production method of the present invention has high stability at normal temperature (23 °C to 25 °C) in the atmosphere, so it is easy to handle and is suitable for the production of products such as electronic components (multilayer ceramic capacitors, thin film capacitors, piezoelectric elements, capacitors, etc.) including a layer containing ferroelectric perovskite-type RbNbO3.

Examples

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

[0020] Example 1 In advance, 99% pure Rb2CO3 powder heated to 300 °C in the atmosphere to remove adsorbed moisture and 99.99% pure Nb2O5 powder were weighed and mixed in a glove box based on a molar ratio of 1:1 and such that the amount of Rb element was 1 to 5% in excess with respect to the Nb element. Then, the obtained mixed powder was heated (sintered) at 800 °C for 10 hours in a box-type electric furnace in the atmosphere to obtain RbNbO3 in the normal pressure phase. The obtained RbNbO3 in the normal pressure phase was stored in a glove box. Next, approximately 0.5 grams of atmospheric pressure phase RbNbO3 was packed into a gold cell in a glove box, and heat treatment was performed 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. After that, 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, when an X-ray diffraction pattern of this crystal was obtained using a Rigaku X-ray diffractometer "SmartLAB" (product name) using Cu-Kα rays, it was found to be perovskite-type RbNbO3, as shown in Figure 2. Furthermore, analysis using the Rietveld method and single-crystal X-ray diffraction revealed that the obtained perovskite-type RbNbO3 is an orthorhombic crystal with space group Amm2 symmetry, and that its lattice constants are a=3.9937(2)Å, b=5.8217(3)Å, and c=5.8647(2)Å.

[0021] Furthermore, the relative permittivity of the perovskite-type RbNbO3 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 manufactured by Agilent or similar. Specifically, the surface of the perovskite-type RbNbO3 crystal was polished using abrasive paper, and then gold for electrodes was deposited on both sides using a sputtering apparatus. Silver wires were attached to these electrodes using Dotite and connected to an LCR meter to measure the relative permittivity. In the case of single crystals, the entire surface of the sample was directly covered with Dotite without polishing, and the relative permittivity was measured while changing the frequency with silver wires attached, obtaining the graph shown in Figure 3. From Figure 3, it can be seen that the obtained perovskite-type RbNbO3 is a ferroelectric with a relative permittivity of 500 or more. [Industrial applicability]

[0022] The ferroelectric perovskite-type RbNbO3 of the present invention is suitable as a raw material for manufacturing multilayer ceramic capacitors, thin-film capacitors, piezoelectric elements, capacitors, etc.

Claims

【Request Item 1】 A ferroelectric perovskite-type RbNbO characterized by having a relative permittivity of 500 or more at 23°C. ３ . 【Request Item 2】 The ferroelectric perovskite-type RbNboO described in claim 1 ３ A method for manufacturing, RbNbO in atmospheric pressure phase ３ A ferroelectric perovskite-type RbNbO is characterized by comprising a sintering process in which the material is heat-treated at a pressure of 3 GPa or higher and a temperature T1 of 650°C or higher. ３ A method for manufacturing this product. 【Request Item 3】 Furthermore, the ferroelectric perovskite-type RbNbO according to claim 2 further comprises a cooling step of lowering the temperature of the sintered material 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 manufacturing this product.

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