Abstract

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The potential solid electrolytes, MgZr4P6O24 and MgHf4P6O24 were prepared using modified novel sol-gel method. Structural and electrical properties of the solid electrolytes were determined. TGA-DSC analyses indicated that the pure dried xerogel powders, when calcined at 900 oC converts to pure single phase MgZr4P6O24 and MgHf4P6O24 nanopowders with excellent crystallinity. Pellets of 13 mm diameter and 3.8 mm thickness made by uniaxial compression were respectively sintered at 1300 oC. Powder XRD analyses indicated that crystalline phase of MgZr4P6O24 and MgHf4P6O24 nanoparticles exhibit monoclinic structure with crystallite size of approx. 39 mm and 42 mm, respectively. The sintered pellets were stable from 1000 oC to 1300 oC, with MgHf4P6O24 solid electrolyte showing no trace of coexistent second phase at higher temperatures. Relative density analyses of sintered MgZr4P6O24 and MgHf4P6O24 pellets yield optimum density of approx. 99% and 98% at 1300 oC, respectively, which are in perfect agreement with SEM-EDS analyses of the sintered pellets. Using impedance spectroscopy, the bulk ionic conductivity of the platinum-cured sintered MgZr4P6O24 and MgHf4P6O24 pellets were determined as 7.23 x 10-3 Scm-1 at 725 oC and 4.52 x 10-4 Scm-1 at 747 oC, respectively. Activation energy of MgZr4P6O24 (Ea = 0.84±0.04eV) and gHf4P6O24 (Ea = 0.74±0.02eV) solid electrolytes indicating MgZr4P6O24 solid electrolyte as possessing improved Mg2+-ion conducting mobile species at high temperatures. However, both solid electrolytes find suitable applications in electrochemical devices.

Keywords: Sol-gel synthesis, Solid electrolyte, MgZr4(1-x)Hf4xP6O24, Structural analysis, Electrical Properties, Electrochemical devices