Structural Properties and Thermal Stability of Bi8Pb5O17Fast Ion Conducting Phases

Samples with Bi8Pb5O17stoichiometry were synthesized by ceramic techniques at temperatures ranging from 200 to 640°C. Their structural properties and relative stabilities were investigated using X-ray and electron diffraction, differential scanning calorimetry, and Raman spectroscopy. The tetragonal2phase is described by an incommensurately modulated structure, whose modulation depends on the firing temperature. Heat treatments in the 200–300°C range lead to the formation of a new tetragonal phase,, which is converted back to2above 300°C. The intermediatephase can be obtained without the previous formation of2, and its X-ray powder diffraction pattern is indexed using a triclinic cell. The present data suggest that the2phase is the low-temperature polymorph of this composition.