Temperature evolution of structural and electrical property for Sr7Mn4O15 at high temperature

Temperature dependence of structural evolution for single phase Sr7Mn4O15 is determined using the in-situ X-ray diffraction with Rietveld refinements in the temperature range of 300-1200 K. It's found that thermal expansion of Sr7Mn4O15 lattice parameters increase linearly with temperature. The structure of face-sharing clusters prefers expansion in the transverse, and corner-sharing clusters prefers the stretch in the longitudinal. Resistance decreases sharply with increasing temperature at high temperature, which means that the Sr7Mn4O15 is a well candidate in applications as negative temperature coefficient thermistor. Based on the fitted atomic parameters given from Rietveld refinements, temperature dependent band gap of Sr7Mn4O15 is estimated with first principle calculation, which exhibits a dramatic reduction from 1.141 eV to 0.349 eV with increasing the temperature.