JPS63144198A - Ferroelectric single crystal - Google Patents

Abstract

PURPOSE:To obtain a readily and precisely machinable ferroelectric single crystal, having excellent processability in cutting and grinding and readily dividable into single domains, by partially substituting Pb in a PbTiO3 single crystal with Mg. CONSTITUTION:The aimed ferroelectric single crystal, obtained by partially substituting Pb in a PbTiO3 single crystal with Mg and having a composition expressed by the formula (0<x<=0.5). This ferroelectric single crystal is produced by preparing a melt of a PbO-PbTiO3 based blend using a crucible made of, e.g. magnesia single crystal, and growing a single crystal by a flux or flux pulling up method. The ferroelectric single crystal can be readily divided into single domains by weak electric field treatment and the single crystal in the single domains has improved electric characteristics, e.g. resistivity, etc. and can be applied to various sensors utilizing excellent pyroelectricity thereof.

Description

[Detailed description of the invention] (Industrial application field) The present invention replaces a part of Pb in a P b T t O3 single crystal with Mg (P b +−x M g x)
The present invention relates to a novel ferroelectric single crystal represented by T i O3 (0x≦0.5).

(Prior art) Recently, PbTi0. is a ferroelectric material with a perovskite structure, has a high Curie temperature of 490°C, and has a pyroelectric coefficient (a
pr /dT) and figure of merit (apr /dT) (
1/ε), it is an industrial material that is beginning to attract attention as a material for pyroelectric infrared detectors.

(Problems to be Solved by the Invention) However, pure P produced by known flux methods, pulling methods, flux raising methods, sputtering methods, etc.
b T i Oy single crystals are extremely brittle (and have many vacancies and crystal defects, and the reality is that their electrical constants have not been measured in most cases. According to a reported example, the resistivity at room temperature is lOhΩ・c11
Only about 1 was obtained. In addition, for the purpose of improving this resistivity, for example, if impurities such as trivalent metal oxides are added, the resistivity will improve, but other electrical properties will deteriorate and the final material will become pyroelectric. It had the disadvantage of lowering the coefficient and figure of merit. Furthermore, since the P b T i O:l crystal produced by the conventional method has many twin structures, the number varies from V/cra to 50KV/
There was also a drawback that it could not be easily converted into a single domain even if strong electric waste treatment of about cm was applied.

(Means for Solving the Problems) The present invention was invented in view of the above-mentioned points. A completely new ferroelectric single crystal (P b+-x Mgx )T i 03 (0<
x≦0.5).

The configuration of the present invention will be explained below.

That is, the gist of the present invention is that P b
General formula (P b+-x Mgx ) in which a part of Pb in the T i O:l single crystal is replaced with Mg T i O:
1 (0<x≦0.5).

Next, to explain the means for obtaining such a ferroelectric single crystal, pbOP b T using magnesia single crystal (purity of 99.99% or more) as a ferroelectric single crystal growth crucible material and PbO as a flux is used. A desired ferroelectric single crystal can be obtained by growing a crystal from an iO3-based melt by a flux method or a flux pulling method. Here, the reason why magnesia single crystal is used as a crucible material is that during the process of gradually growing crystals from a high-temperature PbOPbTi0z melt, Mg is eluted from the crucible material and a part of the Pb in the PbTiO3 single crystal is replaced with Mg. As a result, the resistivity of the grown crystal is improved as well as other electrical properties, and ultimately the pyroelectric performance of the material is greatly enhanced.

Further, according to the above-mentioned ferroelectric single crystal growth method, the amount of Mg eluted, that is, PbTi0. The amount of Mg that replaces a part of the single crystal Pb and forms a solid solution is controlled by the holding temperature and holding time, which are the crystal growth conditions.
1T in solid solution (P bl-XMgx ) T i 0
3 (0<x≦0.5) single crystal is obtained. However, as shown in the scanning micrograph in Figure 2, a crystal with a composition of X = 0 becomes a porous and fragile crystal, and
If the composition exceeds , the crystal with the composition will have many bubbles and different phases interposed inside, and will become an opaque crystal, so it is necessary to satisfy the condition of Q<x≦0.5.

In addition, especially when the flux method is adopted as the growth method, it is preferable to place a magnesia single crystal thin plate with a thickness of about 1 to 2 ms above or below the starting raw material powder in the crucible. , the specific gravity of the melt in the melt state is approximately 8.0. Since the specific gravity of the magnesia single crystal thin plate is approximately 3.585, the thin plate is pushed up to the top surface of the melt due to the difference in specific gravity, and as a result, the volatilization of PBO vapor in the high temperature section is significantly suppressed, resulting in a high yield of high quality large single crystals. There are benefits to be gained. In addition to preventing the volatilization of PBO vapor, this magnesia single crystal thin plate is used as an important source of Mg in the crystal growth process, similar to a crucible material.

(Example) Example 1 Using a PbOPbTi0z MgCOx-based compound, the general formula was determined by the flux method for five types of melt compositions of (P b
01-X Mgx ) Xv represented by T i 03
Raised L. In addition, since PBO is used as the flux, PbO:PbTi0° = 80:20 (mol %), the above five mixed powders are placed in a platinum crucible, loaded into an electric furnace, and then heated from room temperature to 20 to 100℃
The temperature was raised at 0°C/hour. After maintaining that temperature for 10 hours, it was slowly cooled to room temperature at a rate of 20° C./hour.

To take out the grown crystal, the entire crucible was immersed in ZN HNOs, and the crucible was heated and stirred to completely remove the flux. The chemical composition of the obtained crystals was determined by atomic absorption spectrometry to be almost the same as that of the starting formulation. Furthermore, as shown in the scanning micrograph in Figure 2, the crystal with the X=O composition is a porous and fragile crystal, and the crystal with the X=0.6 composition has many bubbles and foreign substances inside. Many phases were present, and good quality crystals could not be obtained.

On the other hand, the crystals with the respective compositions of X=0.02, 0.1, and 0.5 were highly transparent ferroelectric single crystals. By the way, the first scanning micrograph of the X-0,022 composition crystal is
As shown in the figure, it was a highly transparent ferroelectric single crystal.

Example 2 A P b OP b Ti O3-based compound adjusted to PbO:PbTfO3 = 80:20 (mol%) was placed in a magnesia single crystal (purity 99.99% or higher) crucible (dimensions: inner diameter 40 x height 50 After loading it into an electric furnace, heat it for 1 hour from room temperature to 1,100°C.
The temperature was raised at a rate of 50°C/hour. After maintaining that temperature for 15 hours, it was slowly cooled to room temperature at a rate of 10°C/hour. Next, the crystals were taken out in the same manner as in Example 1, and the chemical composition of the crystals was determined by atomic absorption spectrometry and fluorescent X-ray analysis. The results are shown in Table 1.

Table 1 Chemical composition of ferroelectric single crystal As is clear from Table 1 above, the obtained crystal was (P
bo, wvz Mgo, axs) It was confirmed that it was a T i 03 single crystal.

Next, the grown crystal is 2.6X2.6Xl,,3
After polishing to the dragon dimensions, it was placed in an electric furnace and cooled in an electric field at a temperature ranging from 600°C to room temperature.

The applied electric field at this time was 100 V/crrr, and the grown crystal was easily made into a single domain. Using this as a measurement sample, dielectric constant (ε), dielectric loss (tan δ), resistivity (ρ), and pyroelectric coefficient (dpr/dT) were measured. The measurement results are shown in Table 2.

Table 2 (Pbo, qvz Mgo, ozs) TiOs
Single Pi crystal (Dn constant) Furthermore, from the temperature characteristics of the dielectric constant, the measurement sample has a Curie temperature T = 489°C, a Curie-Weiss temperature -465°C, a Curie constant C-2, I XIO”C
It turned out to be an excellent ferroelectric single crystal that can

In addition, in Examples 1 and 2, an example was given in which flux property was used as a method for growing a single crystal, but other means such as a pulling method, a flux pulling method, or a sputtering method may also be used as a means for this growing method. No problem, in short, the obtained crystal is (Pb+-xMgx)T
It goes without saying that a ferroelectric single crystal represented by iO* (0x≦0.5) exhibits excellent characteristics as described above.

(Effects of the Invention) As explained above, the ferroelectric single crystal general formula (P b+-x Mgx ) T i 03 (
The single crystal represented by 0<x≦0.5) is a known pure Pb
Ti0. Compared to single crystals, it has excellent workability when cutting and polishing, and has the advantage of being easily precision-processed to about IXIXQ, 5X, for example. In addition, it is easily made into a single domain by weak electric field treatment, and twins are completely removed.

Furthermore, monodomained (Pb, -IMgx)T
i 03 (0<X≦0.5) Single crystal is pure P b
T i 03! Compared to Li crystals, resistivity and other electrical properties can be significantly improved with almost no drop in the Curie temperature, and it is expected that it will be applied to various sensors that utilize its excellent pyroelectric properties. Its value as an industrial material is extremely large.

[Brief explanation of the drawing]

Figure 1 shows a scanning electron micrograph of (P bo, wsMgo, .z) TiQ, single crystal, and Figure 2 shows P
b Shows a scanning electron micrograph of a T i O3 crystal.

Claims (1)

[Claims] General formula (Pb_1_-_xMg_x) TiO_3(
0<x≦0.5).