Growth of iron niobium sulfide single crystals by chemical transport with iodine

Abstract

Single crystals of the intercalation compounds of the Fe-Nb-S system were grown in a sealed evacuated silica tube by the chemical transport method using iodine as a transporting agent. The respective compositions of x S and y S, x R and y R, x G and y G, in the starting material (Fe x SNb y SS 2), the residual material (Fe x RNb y RS 2) and the grown crystal (Fe x GNb y GS 2) were determined by microthermogravimetry of air oxidation of the samples as well as by a wet chemical analysis of the oxidized samples. When the iron content x G was larger than 0.18 some compounds with a stoichiometric ratio Nb/S = 1 2 (Fe x GNbS 2) were obtained; however, when x G was smaller than 0.18, crystals with compositions y G > 1 were always formed. It was found that irrespective of the niobium content y S, the iron content ( x G ≦ 0.25) of the single crystal could be controlled by that of the starting material, since the compositional relationship x S = x G approximately held, until the value of x S exceeded 0.25. However, when x S > 0.25 then x S > x G, and x G could be determined by the total metal concentration ( x S + y S).