Thermodynamic stability of Na2ZrO3 using the solid electrolyte galvanic cell technique

The sodium potential in the test electrode (a) Pt,O2,Na2ZrO3,ZrO2 was measured by using the emf technique employing Na-β″-alumina as the solid electrolyte in conjunction with (b) Pt,O2,Al2O3,NaAl11O17, (c) Pt,O2,Na2MoO4,Na2Mo2O7 and (d) Pt,Na2CO3,CO2,O2 as the reference electrodes over the ranges 880–1045, 700–800 and 850–940 K, respectively. The emf results between electrodes (b) and (c) were utilized for internal consistency checks. From the results on cells formed between (a) and (b) and those on (a) and (c), the standard Gibbs energy of formation, ΔfGo (kJ/mol) of Na2ZrO3 was determined to be −1699.4+0.3652T (K) valid over the temperature range 700–1045 K. The break in the emf data at 1045 K was corroborated by independent TG/DTA measurements carried out on Na2ZrO3 which exhibited an endotherm at 1055 K indicative of a phase transition in Na2ZrO3.