JPS6236323B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing oriented NaNbO ₃ films. NaNbO ₃ has a perovskite structure similar to BaTiO ₃ which exhibits a high dielectric constant, and also exhibits ferroelectricity, making it a promising material as a dielectric voltage material. Generally, a ceramic sintered body is an aggregate of microcrystals, grain boundaries exist, and the crystal axes of each microcrystal are arranged randomly, so that its physical properties indicate the average value of each crystal axis. In oxide dielectric materials,
It is known that crystal orientation increases dielectric constant and piezoelectricity, and mechanical strength increases by reducing crystal grain boundaries. Crystal orientation technology for ceramic materials has recently become an important issue from an industrial perspective. Methods for bringing anisotropy to the electromagnetic properties of sintered ceramic materials include () forming in a magnetic field, () utilizing the topaxial effect, and () hot working by hot pressing. The magnetic material must be a ferrimagnetic material, and in (), a part of the starting material must have significant shape anisotropy. Furthermore, since the method () requires pressurization at high temperatures, it has the disadvantage that it is not suitable for mass production, and furthermore, it is difficult to produce ceramic thin films. In this respect, the present invention is completely different from conventional methods.
This is a NaNbO ₃ film formation method.

The oriented NaNbO ₃ film formation method of the present invention is to completely process NaNbO _{3 or a mixture of NaNbO 3} to which a small amount of a fluxing agent such as boron oxide, borax, sodium silicate, etc. is added in a platinum nozzle at a temperature of 1300 to 1700°C. A ribbon-shaped oriented sodium niobate film is obtained by melting, rolling and ultra-quenching the melt between two quenching plates sandwiched between rubber rollers as shown in Figure 1. . The rapid cooling treatment from a ceramic melt depends on conditions such as material composition, but it either vitrifies it as it is or precipitates a crystalline phase. Even if it crystallizes, it is unlikely to become oriented. The phenomenon of crystal orientation according to the present invention is thought to be related to the fact that unidirectional solidification occurs during the ultra-rapid cooling process of the ceramic melt. That is, the surface portion of the formed film in contact with the two metal quenching plates had a greater quenching effect than the central portion, which created a temperature gradient in the film thickness direction, making unidirectional solidification possible. As a result, it is presumed that crystal orientation occurs in the direction perpendicular to the film formation.

As an example, 4 mol% of boron oxide was added.
By melting NaNbO ₃ powder in a platinum nozzle at 1500°C for 20 minutes and then ultra-quenching it while rolling it with two quenching plates, we were able to obtain an oriented NaNbO ₃ ceramic film with good uniformity. In order to compare the non-oriented NaNbO ₃ synthetic powder and the oriented NaNbO ₃ ultra-quenched film, their X-ray diffraction patterns are shown in FIGS. 2 and 3. Figure 2 was obtained by solid phase reaction.
It is a NaNbO ₃ crystal powder and shows an X-ray diffraction pattern characteristic of a perovskite structure. This crystal is distorted into an orthorhombic crystal at room temperature and can be indexed using a large unit cell, but here we have expressed it using an ordinary unit cell for ease of understanding. Figure 3 shows the X-ray diffraction pattern of an ultra-quenched oriented NaNbO ₃ film, automatically recorded under the same X-ray diffraction conditions as for the synthetic powder. From comparison, it is clear that FIGS. 2 and 3 are NaNbO ₃ films oriented in the {00l} plane.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an ultra-quenching apparatus used in carrying out the present invention. The explanation of each number in the figure is as follows. 1...Platinum nozzle (outer diameter 8 mm, inner diameter 6 mm, length
100mm), 2...Electric furnace (silicon carbide heating element), 3
... Metal plate (stainless steel), 4 ... Rubber roller, 5 ... Wire rope, 6 ... Winding machine, 7 ...
Motor (with clutch and brake). FIG. 2 is an X-ray diffraction pattern of NaNbO ₃ powder, shown for comparison with an oriented sample. FIG. 3 is an X-ray diffraction pattern of the oriented NaNbO ₃ ultra-quenched film obtained according to the present invention. The X-ray diffraction patterns shown in FIGS. 2 and 3 were automatically recorded using copper as an anticathode.

Claims (1)

[Claims] 1. Add a small amount of sodium niobate (NaNbO ₃ ) or a flux such as boron oxide, borax, sodium phosphate, or sodium silicate to it, melt it completely, and pour the ceramic melt between two metal quench plates. A method for producing oriented sodium niobate ceramics in the form of a thin film, which is characterized by dropping the ceramic material onto a substrate, instantaneously rolling it, and ultra-quenching it.