Growth of single crystals of vanadium sulfides and some thermodynamic considerations for the vapor transport process

Abstract

Single crystals of V 5S 8 and V 3S 4 were grown by chemical transport using iodine as a transport agent, by assuming a constant partial pressure of sulfur, P S 2 , within a closed tube system. The composition of both the grown crystals at the cold zone and the residual source material at the hot zone fell near the equilibrium P S 2 -composition isotherms at a P S 2 value above 10 -2 atm . This means that the isotherms seem to be useful in deriving the composition of grown crystals from the known composition of source material, within the P S 2 range between 10 −2 and one atm. At P S 2 lower than 10 −2 atm, non-equilibrium crystallization proceeded. The partial pressures of gaseous species, VI 4, I 2 and I in some sealed tubes were calculated by considering published data, and those of our own indirect estimation. Gaseous VI 4 seems to play an important role for the chemical transport.