Preparation of praseodymium-doped La9.33(SiO4)6O2 apatite-type solid electrolytes and analysis of the conductivity mechanism

Abstract

In order to improve the electrical conductivity of lanthanum silicate oxide electrolyte (LSO), La9.33Pr x Si6O26+1.5x (LPSO) solid electrolyte powder doped with praseodymium was synthesized at 600 °C by urea-nitrate combustion method with lanthanum oxide (La2O3) and Praseodymium nitrate hexahydrate (Pr(NO3)3·6H2O) as raw materials. It is shown that the Pr-doped LSO still have the typical apatite structure and occupy the LaII cation vacancy at the 6h position. Optimal sintering temperature is 1550 °C. La9.33Pr0.5Si6O26.75 reaches the highest conductivity (4.80×10−4 S·cm−1 at 600 ºC). The main factor that Pr-doped improves the performance of LSO is that Pr-doped that introduced more interstitial oxygen ions Oi* and increased lattice volume, so improved the transport efficiency of interstitial oxygen. The secondary factor is the decrease in the concentration of cation vacancy after Pr-doped, which reduced the negative defect stacking centers. Thereby, decreases space drag of interstitial oxygen transport which increases conductivity of LSO. The praseodymium doped to enhancement LSO conductivity mechanism that interstitial oxygen concentration-cation vacancies concentration-lattice volume composite enhancement mechanism was proposed.