Crystal Structure and Ionic Conductivity of a Layered Perovskite, AgLaNb 2O 7

Abstract

A layered perovskite compound, AgLaNb 2O 7, was newly prepared by an ion-exchange reaction. The compound showed an irreversible phase transition at 330°C. The crystal structures of low-temperature and high-temperature phases were determined by the Rietveld analysis for the X-ray powder diffraction patterns. The unit cell is tetragonal with a = 7.7757(4) Å, c = 42.587(2) Å, and Z = 16 with I 4 1/ acd space group for the β-phase (low-temperature phase), and tetragonal with a = 3.8996(9) Å, c = 21.688(5) Å, and Z = 2 with I4/ mmm space group for the α-phase (high-temperature phase). The main structural difference between the two phases is due to the arrangement of silver ions located in the interlayer of the perovskite layers. The ionic conductivity attributed to the interlayer silver ions was observed, but its magnitude was rather small, ∼10 -5 S cm -1 at 25°C. An abrupt decrease in the ionic conductivity was observed at the phase transition temperature. This behavior is discussed on the basis of the crystal structures of the two phases.