Equilibrium phase relationships in the ZnO-In 2 O 3 system were determined between 1100°and 1400°C using solidstate reaction techniques and X-ray diffractometry. In addition to ZnO and In 2 O 3 , nine homologous compounds, Zn k In 2 O k+3 (where k = 3, 4, 5, 6, 7, 9, 11, 13, and 15), were observed. Electrical conductivity and diffuse reflectance of the k = 3, 4, 5, 7 and 11 members were measured before and after annealing at 400°C for 1 h under forming gas (4% H 2 -96% N 2 ). Room-temperature conductivity increased as k decreased, because of increased carrier concentration as well as increased mobility. In general, transparency in the wavelength range of 450-900 nm increased as k increased. Reduction in forming gas resulted in increased conductivity and reduced transparency for all compounds measured. The highest room-temperature conductivity measured, 270 S/cm, was that of reduced Zn 3 In 2 O 6 .

In 2 O 3 exhibits a dramatic increase in solubility of SnO 2 and ZnO when they are cosubstituted into In 2 O 3 . The resultant material, In 2-2x Sn x Zn x O 3-δ with x ) 0-0.4, displays the same order of magnitude conductivity and transparency compared with bulk ITO (tindoped indium oxide). Rapid quenching of In 2-2x Sn x Zn x O 3-δ raises the conductivity and widens the optical bandgap while lowering the optical transmission.

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The electrical conductivity, Hall effect, and thermoelectric coefficient of Zn/Sn-cosubstituted In2O3 (In2 - 2 x Sn x Zn x O3 - δ), undoped In2O3, and indium−tin oxide (ITO) were studied vs cation composition, state of reduction, and measurement temperature (over the range of 4.2−340 K). Carrier contents and mobilities were determined from the Hall coefficient and conductivity in each case. In2 - 2 x Sn x Zn x O3 - δ displays conductivities up to 1 order of magnitude lower than ITO, and the conductivity of the material decreases with increasing cosubstitution, from approximately 860 to 235 S/cm. Reduction of the materials under flowing H2/N2 increases their carrier concentrations and therefore their conductivities. These results are discussed in terms of possible defect and transport models.

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