Synthesis, characterization and time dependent phase transformation of Li0.4WO3 bronze

Abstract

Abstract Lithium tungsten bronzes with a nominal composition of Li0.4WO3 were synthesized by solid state reactions in silica tubes at 973 K and various low pressures. Samples were characterized using X-ray single crystal and powder diffraction, and neutron powder diffraction. The air pressure inside the sealed quartz tubes played roles for the formation of Li0.4WO3 phases with different symmetries. Whereas using a pressure of 10–7 MPa a pure body centered cubic (Im 3 ¯ $\bar 3$ ) tungsten bronze was formed, at higher pressures (>10–7 MPa) a mixture of Im 3 ¯ $\bar 3$ and primitive cubic (Pm 3 ¯ $\bar 3$ m) perovskite tungsten bronzes were observed with pressure dependent phase fractions. While keeping the synthesized samples under open atmospheric conditions the Im 3 ¯ $\bar 3$ phase gradually transformed into a tetragonal perovskite (P4/nmm) tungsten bronze. The slow cubic into tetragonal phase transformation has been explained in terms of the mobility of lithium within two different crystallographic sites.