The δ → ε → γ LiV2O5 "high temperature" phase transitions evidenced by synchrotron X-ray powder diffraction analysis

The structural evolution and the temperature ranges of stability for the delta, epsilon, and gamma phases of the lithium vanadium oxide bronze LiV2O5 are evidenced by use of synchrotron X-ray powder diffraction in the temperature range 100-250 degrees C. It is shown that delta-LiV2O5 is stable below 120 degrees C and that the complete transformation to the high temperature form gamma-LiV2O5 is achieved above 220 degrees C, In the temperature range 120-220 degrees C epsilon-LiV2O5 is the stable polymorph, The temperature dependence of the cell parameters for the phase delta- and gamma-LiV2O5 are measured and the crystal structure of epsilon-LiV2O5 has been determined using the Rietveld method. It crystallizes in the orthorhombic system and at 140 degrees C the cell parameters are a = 11.3552(6) Angstrom, b = 3.5732(2) Angstrom and c = 4.6548(3) Angstrom. Arguments supporting the choice of the space group Pmmn, as for another bronze alpha' NaV2O5, are given. (C) 1999 Academic Press.