ELECTRONIC-PROPERTIES OF BETA-VANADIUM BRONZES LIXNAYV2O5 ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.37) OBTAINED BY THE SOL-GEL PROCESS(Y)

Vanadium bronzes beta-LixNayV2O5 (0.23 less than or equal to x + y les s than or equal to 0.37) have been synthesized by the sol-gel process. These compounds exhibit the monoclinic structure of compounds of the same composition prepared by solid state reaction, but they are obtain ed as thin layers with a highly preferred orientation. Studies of thes e compounds by magnetic susceptibility, electron paramagnetic resonanc e, and electrical conductivity measurements are presented. It is demon strated from magnetic susceptibility and EPR linewidth that the bipola ron model describes accurately the electronic properties of the lithiu m and mixed lithium/sodium bronzes synthesized by the sol-gel process. De-conductivity measurements between 15 and 300 K show that the bronz e conductivities are anisotropic and depend on the nature of the excha nged ion. More complete study on Li0.23V2O5, including ac-conductivity and impedance measurements from 10 Hz to 10 GHz, gives a good correla tion between all the experimental techniques described in this paper. (C) 1995 Academic Press, Inc.