A Thermodynamic Investigation of Cubic Sodium Tungsten Bronze, Na[sub x]WO[sub 3]

Abstract

The partial molar free energy of solution of sodium in cubic sodium tungsten bronze, NaxW03, has been measured in the composition range from x = 0.45 to x = 0.8 and at temperatures between 500° and 800°C. An electrochemical cell using Pyrex as a sodium ion conducting solid electrolyte has been employed. The standard state for sodium is chosen such that the activity of sodium is unity for the composition NaW03. Using this standard state, the partial molar free energy of solution of sodium is ‘16.6 kcal/g atom of sodium in Nao.45W03 and ‘6.1 kcal/g atom of sodium in Na0.8WO3 at 700°C. The thermodynamic factor β In αNa/β In x has been calculated from the variation of the cell emf with composition. The thermodynamic factor is combined with values for the chemical diffusivity of sodium to evaluate the partial sodium ion conductivity in cubic Nao.78WO3. © 1974, The Electrochemical Society, Inc. All rights reserved.