Gallium phosphide is a typical III–V compound semiconductor and is also an important electronic material. The synthesis and single crystal growth of this compound by melt methods is rendered very difficult because of the large phosphorus vapour pressure. A high pressure vessel with internal heating and a quartz reactor was first developed for the direct synthesis of gallium phosphide. The crystal growth was carried out in a second high pressure chamber rated for 100 bars gas pressure and equipped with the paraphernalia for crystal growth. Single crystals of gallium phosphide were grown from the polycrystalline starting material by the vertical Bridgman method and the vapour pressure problem was overcome by encapsulating the melt in a column of molten boric oxide. Both boron nitride and silica were employed as crucibles, and with the former, single crystal rods of 8–10 mm diameter and 10–15 mm length were obtained.

Studies on the single crystal growth of YBa₂Cu₃O_7−x show that the growth conditions have not been optimised yet and they vary in many ways. Here we report the growth of single crystals of YBCO in the size range 0·5–1·2 mm from nonstoichiometric melts. We have made systematic variations in the flux composition (constituting CuO and BaCO₃) in order to arrive at an optimum composition for consistently getting single crystals of size 0·5–1·2 mm. The tetragonal phase was confirmed by X-ray diffraction and single crystallinity by the Laue technique. Superconductivity was confirmed in oxygenannealed crystals.