JPS5815472B2 - crystal growth equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a crystal growth apparatus.

More specifically, a cylindrical crucible is provided in an electric furnace, a seed crystal and a crystal raw material are filled in the crucible, and the crucible is moved through the electric furnace to melt and then solidify the crystal raw material to grow a single crystal; This paper relates to improvements in equipment for growing single crystals using the so-called Bridgman method.

Single crystal growth using the Bridgman method requires (1) easy humidity control;

(2) It should be easy to operate.

For example, Mn
It is used for many large single crystal growths, such as the synthesis of -2n ferrite.

However, a fundamental drawback of this method is that it is difficult to grow a solid solution single crystal with a homogeneous composition.

For example, to explain the conceptual complete solid solution A-B binary system shown in Figure 1, in order to obtain a crystal with the desired composition P, crystal precipitation must always occur in a melt of composition Q. It is necessary to continue from the beginning.

That is, it is necessary to apply a single crystal growth method generally called a traveling solvent method, and the narrower the width of the melt zone formed at this time, the better.

However, conventional single crystal growth equipment using the Bridgman method heats the crucible from outside, and often requires the use of a good thermal conductor such as platinum or graphite as the crucible material, which limits the width of the melting zone. is thick (and it is difficult to maintain this width constant).

Therefore, among the grown crystals, the composition of the initial growth part and the final growth part changes significantly from the desired composition,
Furthermore, the proportion of the composition deviating from the target composition is large, and this tendency is exacerbated as the crystal diameter becomes larger, which is a major drawback in growing solid solution single crystals of high quality and homogeneous composition.

On the other hand, if a strong temperature gradient is applied to the electric furnace in order to narrow the width of the melting zone, the grown crystals will be exposed to the steep temperature gradient for a long time, resulting in thermal strain and cracking. There is.

The present invention eliminates these drawbacks and provides an apparatus capable of easily growing high-quality, large-sized solid solution single crystals of homogeneous composition.

The crystal synthesis apparatus of the present invention will be explained with reference to the drawings.

FIG. 2 is a longitudinal sectional view of the crystal growth apparatus of the present invention.

In the figure, 1 is an electric furnace, 2 is a furnace heater, 3 is a furnace core tube, 4 is a crucible, 5 is an auxiliary heater, 6 is a mesh heater, 7 is a lead wire of the mesh heater, 8 is a crystal raw material introduction pipe, 9 each indicates a seed crystal.

First, a seed crystal 9 with a target composition is placed in the thin part at the bottom of the crucible 4, and a seed crystal 9 with a target composition is placed on top of the seed crystal 9, and a seed crystal 9 with a composition coexisting in equilibrium with the crystal with the target composition is set, for example, in the case shown in Fig. 1, the target composition is set as P. At this time, a powder with a composition Q that coexists in equilibrium with this is put in, then a mesh heater 6 is set, and on top of this a powder blended to the desired composition or a rod-shaped product made by sintering it is placed. The crucible 4 is set at a predetermined position in the electric furnace 1.

The electric furnace 1 may be of any type as long as it can provide a predetermined temperature (for example, in the case of a single crystal with a P composition shown in FIG. 1, it may be one that can stably obtain a temperature T1 of at least a small amount).

Platinum, graphite, etc. are used as the crucible, and the crucible may be determined in consideration of reactivity with the target composition substance and economical efficiency.

The tip of the crucible is slender (with a seed crystal 9 placed at the tip).
It is desirable that the design be such that it is possible to do so.

Although it is most desirable that the shape is cylindrical from the viewpoint of heat uniformity, other shapes such as square or hexagonal shapes are also possible.

The mesh heater 6 has the function of raising the temperature of the crystal raw material near the heater to a predetermined temperature and allowing the melt to pass through. Open mesh or braided heater wires are used.

The crucible 4 set as described above is held at a predetermined position in the electric furnace 1, and the power of the electric furnace 1 is turned on to raise the temperature until the temperature of the crucible 4 is about 50°C higher than the temperature T2 in Fig. 1. Maintain constant low temperature.

At this time, make sure that the top and bottom of the crucible 4 are evenly heated.

Next, an electric current is passed through the auxiliary heater 5 provided at the lower part of the crucible 4 and the lead wire 7 of the mesh heater 6, and the temperature from the vicinity of the mesh heater 6 to the upper part of the seed crystal 9 is set to T2+α (however, α is 50°C). ) so that it is about 3
The temperature is maintained for 0 minutes, and when the system becomes steady, the mesh heater 6 is gradually raised.

In this way, the crystal raw material is melted from the upper part of the mesh heater 6, and the crystals are precipitated from the lower part.

At this time, if vibration is applied to the mesh heater 6 from the outside,
The molten liquid near the mesh heater 6 is stirred, diffusion within the molten liquid is promoted, and so-called cell growth is prevented from occurring, so there is an advantage that the growth rate can be increased.

Cell growth is a phenomenon that is commonly observed when a crystal with a composition different from that of a solution is precipitated, such as the solid solution single crystal that is the main object of the present invention, and is a phenomenon that is commonly observed in the precipitation of a solid phase. If the accompanying solvent is not diffused in time, the shape of the interface between the crystal and the solution will be disturbed, significantly degrading the quality of the grown crystal.

In order to prevent this cell growth from occurring, it is usually sufficient to make the growth rate extremely slow, but this not only takes time for growth but also significantly increases costs.

Once the mesh heater 6 has risen to the top of the crucible and melted all the crystal raw materials, the temperature is gradually lowered and at the same time the mesh heater 6 is removed, the temperature of the electric furnace 1 is gradually lowered to room temperature, and the crucible is taken out. Obtain crystals.

The crystal raw material may be sintered in advance and held in the crucible, but the powdered material is passed into the crucible 4 through the crystal raw material introduction pipe 8 provided at the top in an amount corresponding to the rise of the mesh heater, that is, the crystal growth. may be supplied to

The crystal growth apparatus of the present invention is maintained in a soaking zone in an electric furnace,
A mesh heater melts only the area near the heater, and the melted area is moved to melt and precipitate the crystal raw material, so it is easy to obtain crystals with a homogeneous composition, and because the temperature gradient is small, there is little thermal distortion. It has the excellent effect of efficiently growing high-quality large single crystals.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the composition of crystal precipitation from a solid solution in an AB binary system and temperature, and FIG. 2 is a longitudinal sectional view of the crystal growth apparatus of the present invention. 1: electric furnace, 2: furnace heater, 3: furnace core tube, 4 nil pot, 5: auxiliary heater, 6: mesh heater, 7: lead wire of mesh heater, 8: crystal raw material introduction tube.

Claims (1)

[Claims] 1. A cylindrical crucible is provided in an electric furnace, and seed crystals and crystal raw materials are filled in the crucible and moved through the electric furnace to melt and then solidify the crystal raw materials to form a single crystal. A crystal growth apparatus characterized in that a movable mesh heater is provided in a crystal raw material of a crucible. 2. The crystal growth apparatus according to claim 1, wherein the heater can be vibrated from the outside. 3. In an apparatus for growing a single crystal by providing a cylindrical crucible in an electric furnace, filling the crucible with seed crystals and crystal raw materials, and moving the crucible through the electric furnace to melt and then solidify the crystal raw materials, A crystal growth apparatus characterized in that a movable mesh heater is provided in the crystal raw material, and an auxiliary heater for preheating is provided at the lowest part of the crucible.