High‐Pressure Synthesis of Fully Occupied Tetragonal and Cubic Tungsten Bronze Oxides

Abstract

AbstractA high‐pressure reaction yielded the fully occupied tetragonal tungsten bronze K3W5O15 (K0.6WO3). The terminal phase shows an unusual transport property featuring slightly negative temperature‐dependence in resistivity (dρ/dT<0) and a large Wilson ratio of RW=3.2. Such anomalous metallic behavior possibly arises from the low‐dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze KxWO3‐K0.6−yBayWO3 phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO3 phase was also identified as a line phase—in marked contrast to NaxWO3 and LixWO3 with varying quantities of x (<1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended.