Mixed valency in the high-temperature phases of transition metal molybdates, AMoO4 (A=Fe, Co, Ni)

Abstract

Transition metal molybdates of the formula AMoO4 where A=Fe, Co or Ni exhibit a first-order phase transition between 670K-970K. An investigation of the lowtemperature (lt) and high-temperature (ht) phases by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, magnetic susceptibility and other physical methods shows that the phase transition is associated with a valence change of the type A2++Mo6+αA3++Mo5+ in the cases of iron and cobalt molybdates. © 1986 Indian Academy of Sciences.