Electrical Properties of Lanthanum Silicate Apatite Electrolytes Prepared by na Innovative Chemical Route

Abstract

This work reports the synthesis of apatite-type lanthanum silicate powders with nominal composition La10Si6O27 by an innovative chemical route which combines co-precipitation and sol-gel approaches. The herein proposed synthetic procedure is advantageous in reducing energy consumption and processing time, key elements to decrease the total manufacturing cost. The as-prepared powder was calcined between 500 and 900 °C. Structure of the calcined powders, characterized by X-ray diffraction (XRD) and Rietveld refinement, indicated the formation of apatite crystalline lanthanum silicate with minor amount of L2O3 at 900 °C. The apatite powder was further analyzed by scanning electron microscopy (SEM). The effect of sintering temperature, ranging from 1400 to 1450 °C, on the electrical properties was investigated by impedance spectroscopy. Electrical measurements were recorded in the 400 – 800 °C temperature range. The lanthanum silicate electrolyte sintered at 1450 °C exhibited total electrical conductivity (σ700 ºC = 2.12 x 10-3 S.cm-1) comparable with samples from literature prepared by sol-gel and freeze drying methods and sintered at 1500 °C. The results in the present study demonstrate that the co-precipitation method combined with a sol-gel approach is a promising alternative route to synthesize lanthanum silicate powders.