On the origin of the anomalous electrical resistivity of LnMo5O8 (Ln = trivalent rare earth)

Electronic structures of AMo(5)O(8) (A = rare earth, alkaline earth) and the solid solution Sr1-xLaxMo5O8 (x=0-1) were examined using the extended Huckel tight binding method. AMo(5)O(8) phases with divalent A cations (A = Sr, Ca, Eu) are normal semiconductors with small band gap. The Fermi surfaces of Sr1-xLaxMo5O8 (0.0 < x less than or equal to 1.0) and LnMo(5)O(8) (Ln = trivalent rare earth) do not exhibit any nesting. In the electronic structures of LnMo(5)O(8) (Ln = trivalent rare earth) phases, the Fermi level is dominated by the d-orbitals of the Mo(2) atoms of their Mo lo clusters. With decreasing x from 1.0 in Sr1-xLaxMo5O8, the dominance of the Mo(2) atoms at the Fermi level sharply diminishes. Based on this observation, we proposed a probable reason for the weakly semiconducting state above 180 K and the metallic state below 180 K in LnMo(5)O(8) (Ln = trivalent rare earth). (C) 1998 Elsevier Science Ltd. All rights reserved.