Synthesis of binary and multinary metal sulphides by precipitation and their characterisation

• CuS, In2S3, CuInS2 and CuGaS2 are synthesised by precipitation using Na2S.
• Powders acquire crystallinity on heat treatment at or above 473 K.
• Formation of ternary sulphides is accompanied with the evolution of SO2.
• Powders have >90% phase purity with no significant Na contamination.
• Band gap of CuS, In2S3, CuInS2 and CuGaS2 is ∼2, 2.3, 1.3 and 2.4 eV respectively.

CuS, In2S3, CuInS2 and CuGaS2 semiconductors have been synthesised in powder form by precipitation reaction using Na2S·3H2O as a precipitating agent. Precipitated at about 313 K in aqueous medium, the powders of CuS crystallise in covellite (hexagonal) phase and those of In2S3, CuInS2 and CuGaS2 in tetragonal phase on heat treatment in argon atmosphere. The formation of CuS or In2S3 takes place due to the reaction between the metal and bisulphide ions in aqueous phase while that of CuInS2 or CuGaS2 involves solid state reaction between CuS and In2S3 or GaxSy during heat treatment and is accompanied with the evolution of SO2 gas. The powders are nearly monophasic, exhibit nanometric morphology and bear their respective stoichiometric compositions. The direct band gaps of CuS, In2S3, CuInS2 and CuGaS2 measure 2.06, 2.3, 1.34 and 2.38 eV respectively. The method is simple and is extended to the synthesis of CuIn0.8Ga0.2S2 as well.

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