Synthesis,structural and physical properties of the binary molybdenum chalcogenide phase Mo15Se19 and of the related compounds M2Mo15Se19 and M3Mo15Se19 (M=group 1A metal; Sn,Pb;Cd)

We present the synthesis, structure and physical properties of the binary phase Mo₁₅Se₁₉. This material was synthesized at low temperatures by oxidation of In₂Mo₁₅Se₁₉ or In₃Mo₁₅Se₁₉ by HCl gas. X-ray studies show that Mo₁₅Se₁₉ can exist in two crystallographic forms depending upon the indium phase used as starting material. Both phases contain large open channels and crystallize in a hexagonal unit cell with lattice parameters $\text{a}{}_{\mathrm{h}}\text{= 9.46}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 19.61}\text{A}\text{?}$ when prepared from In₃Mo₁₅Se₁₉ (space group P6₃/m) and $\text{a}{}_{\mathrm{h}}\text{= 9.48}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 58.76}\text{A}\text{?}$ when prepared from In₂Mo₁₅Se₁₉ (space group R3?c). The two structural forms of Mo₁₅Se₁₉ were found to be superconducting at 4.3K. The ease with which indium can be removed from the ternary compounds without disturbing the binary Mo-chalcogenide networks suggested that other metallic elements could be substituted for indium. In fact, several new M₂Mo₁₅Se₁₉ and M₃Mo₁₅Se₁₉ phases were synthesized, where M = group 1A element; Sn, Pb, and Cd. Several of their physical properties are also reported.