Thermal Expansion of Tetragonal Phase of VO₂

Abstract

Accurate lattice parameters of the tetragonal phase of VO₂ have been determined as a function of temperature by X-ray powder method in the temperature range 78°C to 415°C. Both the lattice parameters are found to increase with increasing temperature, the relative increase in the ‘c’ parameter being greater than that in the ‘a’ parameter. Using the data the coefficients of thermal expansion, α_|| and α_⊥, have been calculated by a graphical method. Temperature dependence of the coefficients are represented by the following equations:
α_||=29.638×10⁻⁶−2.930×10⁻⁸t+2.576×10−¹¹t²
α_⊥=5.828×10⁻⁶−7.091×10⁻⁹t+6.946×10−¹²t²,
where t is in °C.