Effect of divalent dopants on crystal structure and electrical properties of LaAlO 3 perovskite

Abstract

Oxide ion solid electrolytes are materials which exhibit high oxide ion conductivity. In this study, inexpensive perovskite-type oxide, LaAlO 3 was doped with various types of divalent cations. The objective was to investigate the effect of dopants on the crystal structure and conductivity of LaAlO 3. As a result, the solubility of Ca ion into the La cation sublattice was found to be 5 mol% and the solubility of Sr ion could reach 20 mol%. However, only less than 1 mol% Ba ion could be dissolved. In this study, Mg ion was substituted for Al ion in the B-site. The solubility of Mg ion was about 3 mol%. With double doping for A and B parent cations, the addition of Ca, Sr, Ba ion tend to enhance the solubility of Mg ion from 3 to 10 mol%. Although the addition of Mg ion increased the solubility of Ca ion, the solubility of Sr and Ba ion was suppressed. The concentration of oxygen vacancy increases with the increasing amount of divalent cation dopants, within their solubility limits. However, the second phases were found to be stoichiometric compounds without oxygen defects. Thus, the conductivity of second phases was significantly lowered. In the LaAlO 3 perovskite systems, the activation energies for ionic conduction were also significantly influenced by the addition of dopants. The activation energy for singly and doubly doped samples, were about 89–108 and 90–126 kJ/mol, respectively, which is lower than that for undoped LaAlO 3 (∼127 kJ/mol).