Bulk Phase Relations, Conductivity, and Transparency in Novel Bixbyite Transparent Conducting Oxide Solution in the Cadmium‐Indium‐Tin Oxide System

Abstract

A novel transparent conducting bixbyite solid solution In 2−2 x (Cd,Sn) 2 x O 3 (0 < x < 0.34 at 1175°C) has been discovered. Four‐point dc‐conductivity varies widely with x and the [Sn]/[Cd] ratio with a maximum in excess of 1800 S/cm ( x = 0.05, [Sn]/[Cd] = 9) and a minimum too low to be measured ( x = 0.05, [Sn]/[Cd] = 0). The optical gap measured along the line In 2−2 x Cd x Sn x O 3 remains constant near 3 eV while transparency decreases with increasing x possibly because of free carrier absorption. Four‐point dc‐conductivities measured from biphasic samples prepared by varying the [Sn]/[Cd] ratio suggest that the solution extends between the CdO–In 2 O 3 and SnO 2 –In 2 O 3 binaries for small x . As x increases, the solution width decreases and is found to exist only over a small range of [Sn]/[Cd] ratios slightly greater than unity near x = 0.34. Single‐phase bixbyite samples subjected to a reduction anneal showed increased conductivity and slightly higher optical gaps, possibly as a consequence of the Moss–Burstein shift. The ratio of the reduced to as‐fired conductivities for specimens prepared along the line In 2−2 x Cd x Sn x O 3 decreased with increasing x . This suggests that for small x electrons are generated by oxygen vacancies while at larger x the electron population is fixed by a Sn excess (i.e., [Sn]/[Cd] > 1).