A reappraisal of fast ion conduction in Ta, Ga, and Al-substituted Aurivillius phases

Abstract

Oxygen ion conduction in the Aurivillius phases Bi 2Sr 2(Nb or Ta) 2(Ga or Al)O 11.5 has been evaluated in detail. High-temperature X-ray diffraction studies, coupled with differential scanning calorimetry, electron microscopy, and conductivity measurements were used to clearly demonstrate that Bi 2Sr 2(Nb x Ta 1− x ) 2(Ga y Al 1− y )O 11.5 with x = 0, 1 and y = 0, 0.5, and 1 form only multiphase specimens. The origin of the previously observed fast ion conduction is a result of interconnected Bi 2O 3 grains that undergo a high-temperature phase transformation to the δ-Bi 2O 3 polymorph. The Aurivillius phase component of the multiphase specimens does not demonstrate any type of order–disorder transformation, however, the phase transformations of the Bi 2O 3 are clearly observed using high-temperature diffraction and calorimetry.