X-ray diffraction studies of lattice properties in CeX (X = P and As and Yb4As3)

X-ray diffraction experiments were performed in order to study the lattice properties of the low-carrier-density strongly correlated electron systems CeX (X = P and As) and Yb4As3. The lattice constants of CeP and CeAs take minima at 120 and 90 K, respectively, These results are explained by the model in which each crystal-field state is supposed to have its own effective ionic radius. The cell angle of Yb4As3 shows the first-order-like increase from 90.0 degrees to 90.7 degrees accompanied with the charge ordering at T-C = 288 K. It gradually increases to 90.8 degrees with decreasing temperature and is almost independent of temperature below 200 K. The temperature dependence of the cell angle is discussed in connection with the process of the charge ordering. (C) 1998 Elsevier Science B.V. All rights reserved.