LIGHT SCATTERING NEAR THE SEMICONDUCTOR-METAL PHASE TRANSITION IN VANADIUM DIOXIDE.

The temperature dependence of the optical properties of thin vanadium dioxide single crystals was investigated in the neighborhood of the semiconductor-metal phase transition. It was established that the anomaly observed at the phase transition is due to a light scattering effect. A study of the angular dependence of the scattered light intensity and direct examination of the samples in a polarizing optical microscope, made it possible to identify the optical inhomogeneities responsible for this effect. It was shown that they are caused by the coexistence of the two VO//2 phases near the phase transition, and the light scattering effect is due to the marked difference between the optical constants of the two phases, known as the ″transition″ opalescence. An investigation of the transition in individual nuclei of the new phase showed that the temperature of the phase transition was different in different nuclei. This is adduced to explain the ″spread″ of the phase transition temperature. It is proposed that the formation of nuclei of the new phase is associated with the elastic stress fields which are present near defects.