Variation of Defect Structure of Interstitial-Type Oxide Ion Conductors Due to Milling and Its Effects on the Low-Temperature Heat Capacity

Abstract

This review describes the defect contribution of La-doped PbWO₄ oxide ion conductors in terms of low-temperature heat capacity by comparing the sets of samples prepared by sintering and mechanical alloying (MA) methods. The heat capacities of the sintered samples with oxide ion interstitials are slightly larger than those of MA samples with essentially no interstitials around 100 K, because of the excitation of oxide ion motion as well as the lattice distortion caused by the presence of the interstitials. In addition, the variations of defect structure and heat capacity value due to milling the sintered samples are studied; oxide ion interstitials disappear rapidly during the milling process while the vacancy formation at all the general site accompanied by the softening of lattice proceed gradually. Precise heat capacity data with the help of powder density and neutron diffraction results reveal some meaningful aspects of the defect and conduction properties of the oxide ion conductors.