The crystal structure of a new oxide ion conductor NaBi3V2O10 and oxide ion conductivity in Pb2Bi2V2O10

Rietveld refinements using neutron diffraction data have been used to determine the crystal structure of the room temperature polymorph of a new oxide ion conductor, NaBi3V2O10. The cell is isostructural with Pb2Bi2V2O10 and the data refined in spacegroup P1 with cell parameters of a=7.0613(8), b=7.2086(8), c=5.5343(10) Angstrom, alpha=113.328(4), beta=84.4787(14) and gamma=112.249(3)degrees with an R value of 2.19%. The low symmetry of Pb2Bi2V2O10 and NaBi3V2O10 is attributed to structural distortions associated with electron lone pairs on Pb+II and Bi+III. Replacement of Pb+II by Bi+III and Na+I produces a structural phase transition to a higher symmetry polymorph in NaBi3V2O10 at ca. 575 degrees C. ac Impedance measurements show Pb2Bi2V2O10 to be a modest oxide ion conductor with conductivity of ca. 1 mS cm(-1) at 800 degrees C. As a result of the phase transition in NaBi3V2O10 its conductivity is ca. one order of magnitude greater than that of Pb2Bi2V2O10 at 600 degrees C.