Mn0.15V0.3Mo0.7O3, a new compound in the MnV2O6-MoO3 system

摘要

In the past we studied the system MnV2O6 (monoclinic, C2/m, brannerite-type structure)-orthorhombic MoO3, including the Mn Phi = Mn(1-x)Phi(x)V(2-2x)Mo(2x)O(6) solid solutions (Phi = cation vacancy in the original Mn site, X = 100x). Mn Phi's isomorphous with the MnV2O6 matrix appeared to be stable upto X-sat = 42 at room temperature or atmost X-sat = 45 at 520 degrees C. Beyond these limits, Mn Phi(sat) and o-MoO3 were observed to coexist. Now, a new phase Mn0.15V0.3Mo0.7O3 = Mn0.3V0.6Mo1.4O6 (or almost, referred to as the Y phase) has been identified in the MnV2O6-MoO3 system at formal X = 70. It is monoclinic P2/m (P2 or Pm) with a = 11.829(2) Angstrom, b = 3.657(1) Angstrom, c = 10.330(2) Angstrom, beta = 101.54(1)degrees, and V = 437.8(3) Angstrom(3). The Y phase prepared by a citrate precursor method starts to show reasonable (broadened) XRD reflections at 300 degrees C, becomes predominant at 450 degrees C, and decomposes slowly to Mn Phi(sat) and o-MoO3 at higher temperatures (above 450 degrees C). Apparently, due to the parallel course of the solid state reactions, an entirely pure Y phase has never been obtained. Samples with 65 less than or equal to X = 70 always contain some o-MoO3 traces whereas those with 70 = X greater than or equal to 80 are contaminated with Mn Phi(sat). (C) 1998 Academic Press. [References: 11]