Flux method or high temperature solution growth method
This method is similar to growth of CuSO4 from its liquid solution. Where we dissolve CuSO4 in the water solution. We gradually add CuSO4 in the water. At one point we cannot add anymore CuSO4 once the solution becomes saturated. We can heat the solution, and add more amount of CuSO4. Now if we allow the solution to cool down, the extra amount of CuSO4 tries to solidify. And if we allow enough time to cool, they solidify in a crystalline form.
In our case, we are interested in growing metallic single crystals. We need to find a good solvent for metal (water is cannot dissolve metals). But there are metals, which can dissolve another metal. For example, tin (Sn) is a good solvent of many other metals. The melting point of tin is 230 °C. Generally, we take the elements and flux in the ratio (atomic) of 5% : 95%. We take everything in a alumina crucible, then seal in the vacuum inside a quartz tube., and heat up to about 700 - 900 °C (depending on the compound we want to grow single crystal). We hold the melt at highest temperature for several hours for proper homogenization. Then we cool down very slowly, say at a rate of 1 °C/hour, below the melting point of the compound we are growing.
If we cool down to room temperature, the single crystal will be inside the solid tin. In order to separate the crystal from the tin, we need to heat it about 300 °C, and decant the molten tin by using a centrifuge.