Phase relationships, transparency, and conductivity in the cadmium indate-cadmium stannate system

A novel transparent conducting spinel solid solution Cd1+xIn2-2xSnxO4 (0 le ss than or equal to x less than or equal to 0.75 at 1175 degrees C) between cubic CdIn2O4 and orthorhombic Cd2SnO4 has been discovered, The extent of this solid solution is noteworthy given that bulk phase relations determine d in air over the temperature range 800-1175 degrees C demonstrate that cub ic (spinel) Cd2SnO4 is metastable. Reduced samples exhibit exceptional four -point de conductivities exceeding 3500 S/cm (x = 0.70). The maximum optica l gap estimated from diffuse reflectance spectra is similar to 3.0 eV for 0 less than or equal to x less than or equal to 0.15. The optical gap shows negligible change with reduction, possibly because of combined Moss-Burstei n and band-narrowing effects. Abrupt conductivity increases and optical gap decreases at specific compositions, i.e., x = 0.4 and 0.2 respectively, ma y be indicative of a change in cation distribution between tetrahedral and octahedral sites. Room temperature thermopower measurements indicate the ch ange in conductivity across the solution is a consequence of an increase in carrier density and that mobility remains relatively constant.