Forcing substitution of tantalum by copper in 1T-TaS 2 : synthesis, structure and electronic properties of 1T-Cu x Ta 1− x S 2

Abstract We investigated the compound 1T-Cu x Ta 1− x S 2 with respect to its synthesis, homogeneity range, structure and electronic properties. The average structure of 1T-Cu x Ta 1− x S 2 resembles that of the high-temperature phase of the layered transition metal dichalcogenide 1T-TaS 2 in which tantalum is partially substituted by copper. 1T-Cu x Ta 1− x S 2 readily decomposes at elevated temperatures and can only be prepared and stabilized by a sufficiently high amount of sulfur excess. XPS and NEXAFS measurements reveal that copper has the oxidation state +I in 1T-Cu x Ta 1− x S 2 , which is supported by quantum chemical calculations. The disorder introduced by copper doping causes an Anderson-type localization of the conduction electrons as manifested by a strong increase of the electrical resistivity and a Curie-type paramagnetism at low temperatures as in other doped systems 1T- M x Ta 1− x S 2 with higher valent metals. Quantum chemical calculations support this interpretation.