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

A 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 (d rho/dT < 0) and a large Wilson ratio of R-W = 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.