JPH034520B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing ferroelectric single crystals used in piezoelectric and pyroelectric materials, and in particular, to
In the process of growing a PbTiO ₃ single crystal from a PbTiO _{3 -} based melt, a new strong crystal, expressed as (Pb _{1-x Mg} The present invention relates to a method for manufacturing a dielectric single crystal. (Prior art) In recent years, PbTiO ₃ is a ferroelectric material with a perovskite structure and has a high Kyrie temperature of 490°C.
It is attracting attention as a material for pyroelectric infrared detectors due to its large pyroelectric coefficient (dpr/dT) and figure of merit (dpr/dT) (1/ε) compared to other ferroelectric materials (e.g., BaTiO ₃ ). It is done. (Problem to be solved by the invention) However, so far, the pure PbTiO ₃ crystals that have been produced are extremely brittle and have many vacancies and crystal defects, and they have almost no electrical power. The reality is that the various constants have not yet been measured, and according to the few reports, the resistivity at room temperature is only about 10 ⁶ Ωcm. Therefore, for the purpose of improving this resistivity, for example, when adding impurities such as trivalent metal oxides, the resistivity improves, but on the other hand, it deteriorates other electrical properties and the final There was a problem that the pyroelectric coefficient and figure of merit of the material were reduced.
Furthermore, since the PbTiO ₃ crystal produced by the conventional method has many twin crystal structures, it is possible to
It also had the drawback that it could not be easily converted into a single domain even if treated with a strong electric field of about cm. (Means for solving the problems) The present invention was invented in view of the above-mentioned problems. A new ferroelectric single crystal (Pb _1-x Mg _x )TiO ₃ (0<x
≦0.5). The configuration of the present invention will be explained below. That is, the gist of the present invention is as follows:
In the process of growing PbTiO ₃ single crystal from PbO-PbTiO ₃ system melt, by using magnesia single crystal as a crucible material for growing ferroelectric single crystal,
General formula in which part of Pb is replaced with Mg (Pb _1-x Mg _x )
A method for producing a ferroelectric single crystal, characterized by growing a single crystal represented by TiO ₃ (0<x≦0.5). Here, in the production method of the present invention described above, the reason why it is used as a growth crucible material for magnesia single crystals is that in the process of gradually growing crystals from a high-temperature PbO-PbTiO ₃ system melt, Mg is eluted from the crucible material. This is to replace part of the Pb in the PbTiO ₃ single crystal with Mg. The result is improved resistivity of the grown crystal as well as other electrical properties, ultimately significantly increasing the material's pyroelectric performance. The growth method is preferably a flux method or a flux pulling method, but in particular, when the flux method is used, a magnesia single crystal thin plate with a thickness of about 1 to 2 mm is placed above or below the starting material powder in the crucible. By placing , the specific gravity of the melt in the melt state is about 8.0, and the specific gravity of the magnesia single crystal thin plate is about 3.585, so 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 thin plate is pushed up to the top of the melt.
The volatilization of PbO vapor is significantly suppressed, and larger single crystals of better quality can be obtained in high yield. In addition to preventing the volatilization of PbO vapor, this magnesia single crystal thin plate will be used as an important source of Mg in the crystal growth process, similar to the crucible material. Furthermore, in the above growth means, the amount of Mg eluted, that is, the amount of Mg that replaces a part of the Pb of the PbTiO ₃ single crystal and forms a solid solution, is controlled by the holding temperature and holding time, which are the crystal growth conditions.
As a result, the desired amount of Mg was dissolved in solid solution (Pb _1-x Mg _x )
A TiO ₃ (0<x≦0.5) single crystal is obtained. however,
As shown in Figure 2, a scanning micrograph of a crystal with a composition of X=0 shows that it is a porous and fragile crystal.
When X exceeds 0.5, the crystal with the composition has many bubbles and foreign phases interposed inside, and is an opaque crystal. (Example) 50 g of PbO-PbTiO ₃ -based compound adjusted to PbO:PbTiO ₃ = 80:20 (mol%) was placed in a magnesia single crystal crucible (purity 99.99% or more, dimensions: inner diameter 40 x height
50mm, outer diameter 60mm x height 60mm), and on top of that, a magnesia single crystal thin plate (purity of 99.99% or more,
Dimensions: 39 mm diameter x 1.7 mm thickness) was placed and the lid was placed.
This was placed in a denser alumina crucible (99.5% purity or higher, dimensions: outer diameter 78 mm x height 125 mm), loaded into an electric furnace, and then heated from room temperature to 1100 °C at a rate of 200 °C/hour. After holding that temperature for 10 hours,
It was slowly cooled to room temperature at a rate of 10°C/hour. To take out the grown crystals, the entire crucible was immersed in 2N-HNO ₃ and the flux was completely removed by stirring while heating the crucible. A scanning micrograph of the obtained crystal is shown in Figure 1, and atomic absorption analysis and fluorescence
The chemical composition of the crystals determined by line analysis is shown in Table 1.

[Table] As is clear from Table 1, it can be confirmed that the obtained crystal is a (Pb _0.978 Mg _0.022 TiO ₃ single crystal.) Next, the grown crystal was polished to a size of 2.0 x 2.0 x 1.0 mm. After processing, it was placed in an electric furnace and cooled in an electric field at a temperature range from 600°C to room temperature.The applied electric field at this time was 100V/cm, and the grown crystal was easily made into a single domain.This was used as the measurement sample. The 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] Furthermore, from the temperature characteristics of the dielectric constant, the measurement sample has a Curie temperature Tc = 489℃ and a Currie-Weiss temperature To =
It was an excellent ferroelectric single crystal with a temperature of 465°C and a Curie constant c=2.1×10 ⁵ °C. In addition, although the example uses the flux method as the growth method, crystals grown by the flux pulling method are also expressed as (Pb _1-x Mg _x )TiO ₃ (0<x≦0.5). It goes without saying that a ferroelectric single crystal that is made of ferroelectric material exhibits excellent characteristics as described above. (Effects of the Invention) As explained above, according to the manufacturing method of the present invention, in the process of growing a PbTiO ₃ single crystal from a PbO-PbTiO ₃ system melt, a part of Pb is replaced with Mg (Pb _{1 -x} Mg _x ) TiO ₃ (0<x≦0.5) single crystals have the advantage of being relatively easy to obtain on an industrial scale. Also obtained (Pb _1-x Mg _x )
TiO ₃ (0<x≦0.5) single crystal has excellent workability during cutting and polishing compared to conventional porous and brittle PbTiO ₃ crystals.
The machining accuracy is extremely high, allowing for easy precision machining down to around 0.5 mm. Furthermore, it can be easily made into a single domain by weak electric field treatment, and the resistivity and other electrical properties can be significantly improved with almost no drop in the Curie temperature, so it can be applied to various types of sensors that take advantage of its excellent pyroelectricity. There is expected.

[Brief explanation of the drawing]

FIG. 1 shows a scanning electron micrograph of a (Pb _0.978 Mg _0.022 ) TiO ₃ single crystal produced by the production method of the present invention, and FIG.
A scanning electron micrograph of a _PbTiO3 crystal is shown.

Claims (1)

[Claims] 1. In the process of growing a PbTiO ₃ single crystal from a PbO-PbTiO ₃ system melt, by using a magnesia single crystal as a crucible material for growing a ferroelectric single crystal, a part of Pb can be replaced with Mg. A method for producing a ferroelectric single crystal, which comprises growing a single crystal represented by the substituted general formula: (Pb _1-x Mg _x )TiO ₃ (0<x≦0.5). 2. A method for producing a ferroelectric single crystal according to claim 1, characterized in that crystal growth from a PbO-PbTiO ₃ melt is carried out by a flux method or a flux pulling method. 3 In the method described in claim 1, when growing crystals by the flux method, by placing a magnesia single crystal thin plate above or below the starting material in the crucible, PbO in the melt state can be grown.
A method for producing a ferroelectric single crystal characterized by suppressing volatilization of vapor.