JPH0678199B2 - Method for producing single crystal of garnet ferrite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a garnet ferrite single crystal used for an optical isolator used for optical communication and an optical CT that is a current or magnetic field sensor using light. To improve the method of manufacturing.

(Prior Art) Conventionally, a flux method and an LPE method (liquid phase epitaxial method) have been widely used as a method for producing a garnet ferrite single crystal.

In the flux method, a raw material containing constituent components of garnet ferrite such as yttrium oxide, rare earth oxides and iron oxide, and a flux of lead oxide, lead fluoride, boron oxide, bismuth oxide, etc. are put in a crucible made of platinum, for example. After uniformly melting, single crystals of garnet ferrite are grown by slow cooling or evaporation of flux.

However, in this method, it takes a long time to grow a single crystal,
In addition, it is inevitable that impurities such as the used flux and crucible are mixed.

Further, the LPE method is a method in which a raw material containing the constituent components of garnet ferrite as described above and a flux are uniformly melted in a crucible, and then a single crystal of garnet ferrite is epitaxially grown using a nonmagnetic garnet single crystal as a substrate. is there.

In this LPE method, although the single crystal growth time is shorter than that in the flux method, the use of flux and crucible is the same, and it is inevitable that impurities are mixed.

When impurities other than trivalent, such as Pb ²⁺ and Pt ^4+, are mixed in the garnet ferrite single crystal among these impurities, the ionic valence of iron ions is changed. Therefore, there is a problem that the optical characteristics of the garnet ferrite single crystal are mainly deteriorated.

Further, in these methods, since a crucible made of a precious metal such as platinum is usually used, there is a problem that the manufacturing cost becomes high when the crucible is enlarged in response to the demand for increasing the size of the single crystal to be grown. .

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above problems, and a garnet ferrite capable of reducing the manufacturing cost by shortening the growth time of a single crystal, mixing of impurities, and the like. It is an object to provide a method for producing a single crystal.

[Structure of the Invention] (Means for Solving the Problems) The method for producing a garnet ferrite single crystal of the present invention is a raw material containing a cation that constitutes a c-site of garnet ferrite or a cation that constitutes an a-site and a d-site. One of the raw materials containing ions is blended in excess of the stoichiometric composition, the raw material powders are mixed, and the raw material powder is fired.

In the method of the present invention, a-site component and d-site component 5
Whether the c-site component is 3.001 to 3.2 mol per mol,
Alternatively, it is desirable to mix the raw materials so that the a-site component and the d-site component are from 5.001 to 5.2 mol with respect to 3 mol of the c-site component.

In the method of the present invention, the c-site component of garnet ferrite is at least 1 selected from Y and rare earth elements.
Species and Ca. When the c-site component is blended in excess, the excess is covered by Ca. As the a-site component and d-site component of garnet ferrite, at least one selected from Sn, Zr, Ti, Ge, Si, V, Sb and Fe, or Sn, Zr, Ti, Ge, Si, V, At least one selected from Sb, at least one selected from Al, Ga, In, Sc and Fe. These a-site component and d-site component are compatible with each other.

(Function) Generally, garnet ferrite is represented by R ₃ Fe ₅ O ₁₂ . This garnet ferrite contains Fe ₂ O ₃
Is dissolved to form (R ₃ Fe _{3u / 4} ) (Fe _{5 + 5u / 4} ) O _{12 + 3u} .

By the way, the composition of a single crystal to be grown by the method of the present invention is represented by a chemical formula: Ca _x R _3-x Fe _5-yz A _y B _z O ₁₂ (I) (where R is Y, a rare earth element At least one selected, A is at least 1 selected from Al, Ga, Sc, In
Species, B is at least one selected from Zr, Sn, Ti, V, Ge, Si, Sb, and the indices x, y, z are determined so as to maintain the overall electrical neutrality). .

Even in a single crystal of this composition, when the c-site component or the a-site component and the d-site component are excessively blended and fired,
It is possible to obtain a single crystal in which the excessively blended components form a solid solution in the composition represented by (I). Then, abnormal grain growth occurs during this firing, and the grain size of the single crystal becomes coarse. Therefore, unlike the case of the conventional flux method or LPE method, it is possible to grow a single crystal without mixing impurities originating from the flux or crucible, and it does not cause deterioration of light absorption characteristics or increase of manufacturing cost. .

As described above, the components to be added in excess are 3 parts of the c-site component for 5 mols of the a-site component and the d-site component.
It is desirable that the amount is 001 to 3.2 mol, or that the a site component and the d site component are 5.001 to 5.2 mol with respect to 3 mol of the c site component. This is shown below in correspondence with the composition formula (I).

Or (However, n is the ionic value of the element B).

Excessive blending of the c-site component or the a-site component and the d-site component within the above range is as follows. That is, when the excess amount of the c-site component or the a-site component and the d-site component is less than 0.001 mol, coarsening of the crystal grain size of the single crystal due to the above-mentioned abnormal grain growth hardly occurs. On the other hand, when the excess amount of the c-site component or the a-site component and the d-site component exceeds 0.2 mol, the amount of different phases existing in the sintered body increases, coarsening of crystal grains does not easily occur, and the different phases are crystallized. It becomes easy to be taken into the grains and its optical characteristics deteriorate.

Further, in the method of the present invention, a single crystal having the same structure as the single crystal to be grown may be inoculated in order to control the orientation and number of the coarsened crystals.

(Example) Hereinafter, the Example of this invention is described. An example in which the c-site component was blended in excess of 3 mols based on 5 mols of the a-site component and the d-site component is shown in Table 1 and the c-site component 3
Table 2 shows examples in which the a-site component and the d-site component were blended in excess of 5 mol per mol. The elements in brackets in the columns of 1 / 2R ₂ O ₃ , 1 / 2A ₂ O ₃ and 1 / nB ₂ O _n in Tables 1 and 2 represent R, A or B, respectively.

Examples 1 to 16 and Comparative Examples 1 and 2 (Table 1) Examples 21 to 36 and Comparative Example 3 (Table 2) First, aiming at the compositions shown in Tables 1 and 2 below,
Y ₂ O ₃ , Gd ₂ O ₃ , CaCO ₃ , FeOOH, ZrO ₂ , V ₂ O ₅ , SnO ₂ , TiO ₂ , G
_{eO 2, SiO 2, Al 2} O 3, Ga 2 O 3, Sc 2 O 3, In 2 O 3 were blended were weighed after 24 hours pulverized and mixed in a wet ball mill, and dried. Next, each of the obtained mixed powders was granulated, and the granulated powder was filled in an alumina crucible and calcined in the air at 1100 ° C. for 4 hours. Subsequently, the calcined body was ground again with a wet ball mill and then dried. The obtained powders had the compositions shown in Table 1 and Table 2, respectively.

Subsequently, an appropriate amount of polyvinyl alcohol aqueous solution was added to each powder and press-molded at a pressure of 1 ton / cm ² to obtain pellets having a diameter of 20 mm and a thickness of 5 mm. Then, each pellet was fired in an oxygen flow at a temperature shown in Tables 1 and 2 for 8 hours to obtain a sintered body.

The density of the obtained sintered body was measured by the Archimedes method, and the relative density (%) to the theoretical density was calculated. The surface of the sintered body was polished and then etched to measure the average particle diameter of the sintered body constituent particles and the maximum crystal particle diameter of the single crystal. The results are shown in Table 1 and Table 2, respectively. The average grain size was determined for crystal grains other than the crystal grains coarsened by abnormal grain growth.

As is clear from Table 1, when the amount of the c-site component is too much as 3.3 mol relative to 5 mol of the a + d-site component (Comparative Example 1) and when the c-site component has a stoichiometric composition of 3.0 mol (comparison In Example 2), the relative density is small and the maximum diameter of the single crystal is also small. The small relative density is
It is considered that this is because pores are present in the sintered body and the densification is not sufficient. In addition, the maximum diameter of the single crystal is small,
It is considered that this is because in Comparative Example 1, the amount of the hetero phase increases due to the excessively blended components, and in Comparative Example 2, abnormal grain growth does not easily occur.

On the other hand, in Examples 1 to 16, the relative density is high and the maximum diameter of the single crystal is large.

Similarly, as is clear from Table 2, when the amount of the a + d site component is excessive (5.3 mol) relative to 3 mol of the c site component (Comparative Example 3), the relative density is small and the maximum diameter of the single crystal is also small. . It is considered that this is due to the same reason as in Comparative Example 1.

On the other hand, in Examples 21 to 36, the relative density was high and the maximum diameter of the single crystal was large.

Example 41 The composition is a molar ratio of 1 / 2Y ₂ O ₃ = 2.94, CaO = 0.10,1 / 2Fe ₂
Predetermined raw materials were mixed so that O ₃ = 4.94 and ZrO ₂ = 0.06, and pellets were molded by the same method as described above. The pellets were fired by changing the firing temperature in the range of 1450 to 1600 ° C to obtain a sintered body. The relative density and average particle size of the obtained sintered body were measured, and the relationship with the firing temperature was investigated. The results are shown in FIG.

From FIG. 1, it can be seen that the garnet ferrite single crystal of this composition is preferably fired in the range of 1480 to 1570 ° C. at which the relative density is close to 100%.

Further, the obtained garnet ferrite single crystal was cut out from the sintered body, subjected to optical polishing treatment, and the absorption coefficient α was measured at a wavelength of 1.3 μm, whereupon α = 0.08 cm ⁻¹ .
In the garnet ferrite single crystal produced by the flux method, considering that α is 0.1 cm ⁻¹ or more even at the best value due to the influence of impurities, the method of the present invention has a large effect of improving the optical characteristics of the garnet ferrite single crystal. I understand.

Example 42 The composition is a molar ratio of 1 / 2Y ₂ O ₃ = 2.94, CaO = 0.06,1 / 2Fe ₂
Predetermined raw materials were blended so that O ₃ = 4.94 and ZrO ₂ = 0.10, and pellets were molded by the same method as described above. The pellets were fired by changing the firing temperature in the range of 1400 to 1550 ° C to obtain a sintered body. The relative density and average particle size of the obtained sintered body were measured, and the relationship with the firing temperature was investigated. The results are shown in FIG.

It can be seen from FIG. 2 that the garnet ferrite single crystal of this composition is preferably fired in the range of 1420 to 1530 ° C. at which the relative density is close to 100%.

Further, the obtained single crystal was cut out from the sintered body, subjected to optical polishing treatment, and then the absorption coefficient α was measured at a wavelength of 1.3 μm. As a result, α = 0.08 cm ⁻¹ . From these results, it can be seen that the method of the present invention has a great effect of improving the optical characteristics of the garnet ferrite single crystal.

As can be seen from Examples 41 and 42, the firing temperature at which the average particle size shows a peak varies depending on the composition, so it is desirable to determine an appropriate firing temperature according to the composition.

Example 43 2 × 2 × 2 mm prepared by the flux method in the center of the raw material powder in a molding die, in which the same raw materials as those in the above-mentioned Example 41 were blended.
Pellets were molded by press molding in the state where ³ Y ₃ Fe ₅ O ₁₂ single crystal (hereinafter referred to as YIG single crystal) was embedded. The YIG single crystal was embedded so that its (110) plane was parallel to the surface of the pellet.

When the pellets were fired at 1500 ° C, the embedded YI
Grain coarsening occurred around the entire pellet centering on the G single crystal, and a garnet ferrite single crystal with a maximum diameter of about 18 mm could be obtained. Also, by X-ray diffraction,
The orientation of the obtained garnet ferrite single crystal is (110).
Was confirmed.

Example 44 The same raw material as in Example 42 above was blended, and the same as in Example 43.
A pellet in which a YIG single crystal was embedded was formed.

When the pellets were fired at 1500 ° C, the embedded YI
Grain coarsening occurred around the entire pellet centering on the G single crystal, and a garnet ferrite single crystal with a maximum diameter of about 18 mm could be obtained. Also, by X-ray diffraction,
The orientation of the obtained garnet ferrite single crystal is (110).
Was confirmed.

Example 45 The same raw material as in Example 41 was blended to form pellets, which were then fired at 1300 ° C. to obtain a sintered body. Each of the sintered body and the YIG single crystal produced by the flux method was mirror-polished, and then both polished surfaces were bonded with an acid.

When this was fired at 1500 ° C., the entire pellet was a single crystal.

Example 46 The same raw materials as in Example 42 were mixed to form pellets, which were then fired at 1300 ° C. to obtain a sintered body. Each of the sintered body and the YIG single crystal produced by the flux method was mirror-polished, and then both polished surfaces were bonded with an acid.

When this was fired at 1500 ° C., the entire pellet was a single crystal.

From the results of Examples 43 to 46, it is understood that it is desirable to inoculate a single crystal having the same structure as the garnet ferrite single crystal to be grown at the time of firing the raw material.

[Advantages of the Invention] As described in detail above, according to the method of the present invention, it is possible to produce a garnet ferrite single crystal which is excellent in optical characteristics without inclusion of impurities without increasing the production cost.
Its industrial value is great.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the firing temperature and the relative density and average particle size of the garnet ferrite sintered body in one embodiment of the present invention, and FIG. 2 is the firing temperature in another embodiment of the present invention. FIG. 3 is a characteristic diagram showing the relationship between the relative density and the average particle size of a garnet ferrite sintered body.

Claims (3)

[Claims] 1. A raw material powder is prepared by blending one of a raw material containing a cation constituting a c-site of garnet ferrite or a raw material containing a cation constituting an a-site and a d-site in excess of a stoichiometric composition. A method for producing a garnet ferrite single crystal, which comprises mixing and firing the raw material powder. 2. The c-site component is 3.001 to 3.2 mol per 5 mol of the a-site component and d-site component, or the a-site component and the d-site component are 5.001 to 5.2 mol per 3 mol of the c-site component. The method for producing a garnet ferrite single crystal according to claim 1, wherein the raw materials are mixed so that 3. The c-site component of garnet ferrite is Y,
It is at least one selected from rare earth elements and Ca, and the a-site component and the d-site component are Sn, Zr, Ti, Ge, Si,
At least one selected from V and Sb and Fe, or Sn, Zr,
At least one selected from Ti, Ge, Si, V, Sb, Al, Ga, I
The garnet ferrite single crystal according to claim 1 or 2, wherein at least one selected from n and Sc and Fe, and the a site component and the d site component are compatible with each other. Manufacturing method.