Abstract
A series of new rare earth compounds Ln2GeBe2O7 (Ln=Y, La, Pr, Sm, Gd, Dy and Er) have been synthesized. With Cu Kα radiations, 1701 powder X-ray diffraction data were collected for each of these compounds by a step scan method with a step interval of 0.05° in 2θ, and the structure analysis of the compounds was carried out by the powder pattern fitting method. Atomic coordinates and isotropic temperature factors were determined by using the least-squares program PFLS-M. The crystals have tetragonal melilite structures composed of layers of GeO4 and BeO4 tetrahedra parallel to (001) and rare earth ions connecting the layers along the c-axis. The c-value decreased with decrease in the ionic radius of the rare earth ions between the layers, showing a typical lanthanoid contraction. The a-axis which is parallel to layers also contacted, since the size of the Be2O7 double pyramids became smaller with decreasing ionic radius of the rare earth ions. Comparing eight-fold coordination sites at interlayers in the present compounds with other melilites, the former was less distorted than the latter. Though the rare earth compounds usually show the magnetic transitions at low temperatures, the present compounds showed paramagnetism down to 4.8K.
