Charge Density Wave and Crystal Structure of K_xWO_3 ( x=0.20 and 0.22) Prepared by Hybrid Microwave Method

Potassium tungsten bronzes K_xWO_3 ( x=0.20 and 0.22) with the coexistence of charge density wave (CDW) and superconductivity (SC) were prepared from K_2WO_4, WO_3 and W powders using a hybrid microwave method. The structure refinement confirmed that all samples had a pure hexagonal phase with the space group of P6_3 / mcm . The distortion degree of W–O octahedron declines with x and is independent of synthesis condition for the same x (=0.20). The CDW transition is studied as a function of residual resistivity ratio. By increasing the crystallinity of sample, this transition can be suppressed, which is probably attributed to the interaction between CDW and defects in crystallites. The CDW transition temperature increases with x , which may be related to the decline of the distortion degree of W–O octahedron. The competition between CDW and SC is observed according to the resistivity and magnetization measurements.