Synthesis, Characterization and Structure-Property Relationship of Alkali Metal Tungsten Bronzes

Abstract

Series of LixWO3 (x = 0.1-0.6) bronzes have been synthesized by solid state synthesis method. Samples with a composition of x = 0.1 (Li0.1WO3) crystallize as perovskite-type tungsten bronze showing orthorhombic symmetry (Pcnb), whereas for x = 0.4-0.6 single phases of cubic symmetry (Im-3) were found. A mixture of two phase products (Pcnb and Im-3) are observed for x = 0.2 and 0.3. Polycrystalline samples of Li0.4WO3 bronzes produced at 973 K for 168 h using a pressure of 10-7 MPa resulted in pure phases showing Im-3 symmetry while using a pressure greater than 10-7 MPa always led to mixed phases showing Im-3 and Pm-3m symmetry. Polycrystalline samples of tantalum and vanadium substituted hexagonal tungsten bronzes of potassium or rubidium (HTB´s) with nominal compositions of A0.3(W1-yTay)O3 (A = K or Rb, y = 0-0.3), A0.3(W1-yVy)O3 (A = K or Rb, y = 0-0.18), and K0.3(W1-yTay/2Vy/2)O3 (y = 0-0.3) were synthesized by solid state reactions at 10-7 MPa and 1073 K. The K-HTB series samples crystallize in space group P6322 while Rb-HTB could be described in space group P63/mcm.