Average and Local Structure of Apatite-Type Germanates and Implications for Oxide Ion Conductivity.

摘要: Materials with the apatite structure have a range of important applications in which their function is influenced by details local structure. Here, we describe an average and structural study to probe origins high-temperature oxide ion mobility La10(GeO4)6O3 La8Bi2(GeO4)6O3 oxygen-excess materials, using low-conductivity interstitial oxide-free La8Sr2(GeO4)6O2 as benchmark. For La10 La8Bi2, locate oxygen, Oint, responsible for conductivity Rietveld refinement relate P63/m P1 phase transitions on cooling oxygen ordering. Local studies neutron total scattering reveal that well-ordered GeO5 square pyramidal groups form at low temperature, but Oint becomes significantly more disordered high-conductivity, structures, transition trigonal-bipyramid-like geometry. We higher Bi materials presence several sites similar energy structure, correlates its less-distorted low-temperature