Soft Chemistry Routes for the Synthesis of Sr_0.02La_0.98Nb_0.6Ta_0.4O₄ Proton Conductor

Abstract

Niobates and tantalates of rare-earth compounds are high temperature proton conductor (HTCP) oxides that are gaining attention as possible stable electrolyte materials for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). Sr 0.02 La 0.98 Nb 0.6 Ta 0.4 O 4 was synthesized by auto-combustion and co-precipitation routes, and by solid state reaction for sake of comparison, expecting an improvement in conductivity for the wet chemistry routes over the conventional solid state reaction method. Single phase materials were obtained at 1100°C by autocombustion and by co-precipitation. The synthesized powders were characterized by X-ray diffraction (XRD) and dilatometric analyses. Dense electrolytes were obtained by pressing the calcined powders into cylindrical pellets and then sintering at 1600°C for 10 h. The pellets were observed by scanning electron microscopy (SEM). Electrical conductivity of the sintered pellets was measured as a function of the temperature by electrochemical impedance spectroscopy (EIS) measurements. Proton conductivity of 2.2×10 -4 S cm -1 was obtained in wet argon atmosphere at 800°C for the sample produced via auto-combustion.