New monoclinic compounds, Bi(3.24)Ln(2)W(0.76)O(10.14), having a pseudo-orthohexagonal cell based on a pseudo-fcc subcell in the systems Bi2O3-Ln(2)O(3)-WO3 (Ln=La, Pr, and Nd)

摘要

New compounds, Bi(3.24)Ln(2)W(0.76)O(10.14), have been found in the systems Bi2O3-Ln(2)O(3)-WO3 (Ln = La, Pr, and Nd). They crystallize ostensibly in the orthorhombic (or orthohexagonal) symmetry, e.g. with a = 6.9694(1) Angstrom, b = 4.0242(1) Angstrom, c = 9.3335(1) Angstrom, and Z = 1 for Ln = La. At the same time, the lattice forms a superstructure based on a pseudo-fcc subcell with a' approximate to 5.6 Angstrom, 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 approximate to90degrees. All new compounds undergo two reversible polymorphic transitions at about 980degreesC and at 1097-1210degreesC depending on Ln. Their electrical conductivity exhibited lower values (about 10(-4) S cm(-1) at 500degreesC) despite the pseudo-fcc subcell in relation to the delta-Bi2O3 type which is the well-known good oxide-ion conductor. (C) 2002 Elsevier Science (USA). All rights reserved. [References: 15]