Synthesis and Properties of Sr1−XLaXMo5O8(0≤x≤1): A New Class of Oxides with Metallic Properties

Single crystal and oriented polycrystal specimens of the solid solution between SrMo5O8and LaMo5O8have been prepared by fused salt electrolysis. The La/Sr ratios of the solid solution members formed are highly sensitive to the melt composition. Both end members of this series are semiconducting at room temperature, with the La compound displaying complex low-temperature behavior. On the other hand the solid solutions become metallic over the range 300–20 K when a few atom % of either La or Sr are present. Detailed structural investigations by single crystal X-ray and powder neutron diffraction at ambient and low temperatures failed to reveal any changes in the Mo–Mo or Mo–O network that would account for the observed anomalies in the electronic properties. The composition-controlled semiconductor-to-metal transition can be explained on the basis of a simple qualitative band model.