Effects of sulphur content on superconductivity and intercalation in transition metal disulphides

Abstract

THE nearly two-dimensional character of the group IVB and VB transition metal dichalcogenides intercalated with organic molecules¹ makes the superconducting metals logical choices for the study of superconductivity in two dimensions. Many anisotropic semiconductors could be used as electronic devices. But scientific investigation has been restricted partly by the quality of available crystals. A number of complexes are metastable at room temperature, and others deintercalate below 150° C. Many intercalation compounds become greatly exfoliated so that measurements of single crystals become quite difficult. Other crystals exhibit little or no registry between adjacent layers. In one case—TaS₂ (pyridine)_½—two phases of intercalated material have been detected. We have found that the addition of sulphur to the intercalate both orders and thermally stabilises the resulting complex. The removal of sulphur by the intercalate increases disorder and thermal instability.