New monoclinic compounds, Bi3.24Ln2W0.76O10.14, having a pseudo-orthohexagonal cell based on a pseudo-fcc subcell in the systems Bi2O3-Ln2O3 -WO3 (Ln=La, Pr, and Nd)

New compounds, Bi3.24Ln2W0.76O10.14, have been found in the systems Bi2O3 -Ln2O3-WO3 (Ln=La, Pr, and Nd). They crystallize ostensibly in the orthorhombic (or orthohexagonal) symmetry, e.g. with , and Z=1 for Ln=La. At the same time, the lattice forms a superstructure based on a pseudo-fcc subcell with , where the transformation matrix is (1/2,1/2,-1)/(-1/2,1/2,0)/(1,1,1). However, the cation configuration has proved that the true symmetry is monoclinic (C2/m) with BETA~90°. All new compounds undergo two reversible polymorphic transitions at about 980°C and at 1097-1210° C depending on Ln. Their electrical conductivity exhibited lower values (about 10-4 Scm-1 at 500°C) despite the pseudo-fcc subcell in relation to the DELTA-Bi2O3 type which is the wellknown good oxide-ion conductor.