| 摘要 |
Electrically conducting (P-type) cubic BN is prepared by heating BN, e.g. hexagonal or cubic, with at least 0.001% by weight of beryllium, in the presence of a catalyst, e.g. 0.1-1%, at a temperature of at least 1200 DEG C., preferably 1500-2100 DEG C., and a pressure of at least 50,000 atm., preferably 60,000-100,000 atm. The Be may be present as a compound decomposable during the heating to Be, e.g. chloride, bromide, iodide, carbonate, nitrate, stearate, nitride, sulphate or oxide. The catalyst may be an alkali metal, alkaline earth metal, Pb, Sb, Sn or nitrides of the foregoing, e.g. Li3N or Mg3N2, and may be mixed as a powder with the BN and Be, or may be a tube containing same. The mixture of powdered BN, Be and catalyst is heated under pressure in a Ta, C or a Ti tube encased in a C tube encased in a compressible ceramic, pyrophyllite, tube which is placed in the apparatus of Specification 860,499. On completion of reaction the BN is obtained by dissolving the matrix in HCl or aqua regia and isolating by hand or using bromoform. The cubic BN formed has a specific resistance of less than 1012 ohm/cm., e.g. 5x103 to 5 x 106 ohm/cm., and is suitable for use as semi-conductors e.g. transistors, rectifiers, thermometers, electroluminescent bodies or a high-temperature catalyst. Specification 860,499 is referred to. |
