Neutron diffraction studies of cubic tungsten bronzes

Abstract

Powder neutron diffraction studies of Li 0.36WO 3, Na 0.73WO 3 and La 0.14WO 3 show them to be isostructural with cubic D 0.53WO 3. Apart from La 0.14WO 3, all have distorted perovskite structures described by a body centered unit cell ( Im3) containing eight formula weights. The distortion, which decreases in the order D ∼ Li > Na creates two crystallographically inequivalent A sites: 12 coordinate (0,0,0) and 4 coordinate ( 1 2 , 1 2 ,0) . Although precise occupation numbers of these sites could not be determined directly, it is probable that the lithium atoms are ordered into the 4 coordinate sites. La 0.14WO 3 has the simple perovskite structure with a random distribution of lanthanum atoms over the 12 coordinate A sites. Comparative features of the cubic tungsten bronze structures are discussed.