Synthesis and Crystallography of New Monoclinic Compounds, Bi_(3.24)Ln_2W_(0.76)O_(10.14), Based on a Pseudo-fcc Subcell in the Systems Bi_2O_3-Ln_2O_3-WO_3 (Ln=La, Pr, Nd)

摘要

New compounds, Bi_(3.24)Ln_2W_(0.76)O_(10.14), have been found in the systems Bi_2O_3-Ln_2O_3-WO_3 (Ln=La, Pr, and Nd). They crystallize apparently in the orthorhombic symmetry, e.g., with a =6,9694 A, b=4,0242 A, c=9.3335 A, and Z=1. Moreover, the crystal lattice is regarded as orthohexagonal and forms a superstructure based on a pseudo-fcc subcell with a=5.6A. The cation configuration, however, has proved that the true symmetry is monoclinic with beta=90 deg. All new compounds undergo two reversible polymorphic transitions at about 980 deg C and at 1097-1210 deg C depending on Ln. the electrical conductivity of them exhibited lower values of about 10~(-4) S cm~(-1) at 500 deg C.