Temperature Dependence of the Optical Absorption Edge of Tungsten Trioxide Single Crystal

Abstract

The optical absorption edge of WO₃ single crystal has been measured with polarized light over the temperature range from −100°C to 900°C. From 0°C to about 700°C, the absorption edge shifts linearly toward red with increasing temperature, the temperature coefficients being −9.0×10⁻⁴ ev/deg for the case of light polarized in the direction parallel to the a-axis(a-polarized light) and −6.5×10⁻⁴ ev/deg for the case of light polarized in the direction parallel to the c-axis(c-polarized light), respectively.
In the vicinity of −50°C, an anomalous shift of the absorption edge takes place. This is attributed to the phase transition. In the low temperature phase, the extinction position is different from that in the high temperature phase. In addition, when the temperature is raised through 740°C, a sudden red shift takes place for the case of a-polarized light, the magnitude being about 0.35 ev, while no anomaly occurs for c-polarized light.