Mechanism of Sm₂MoO₆ phase formation from a mechanically activated oxide mixture

Abstract

The mechanism of phase formation from (1) the initial and (2) the mechanically activated mixture of Sm2O3 + + MoO3 oxides has been studied by DSC in an oxygen atmosphere. It is shown that different mechanisms of samarium oxymolybdate synthesis are realised in these two cases. As a result of the mechanochemical action at room temperature, a nano-sized mixture of Sm2(MoO4)3 and Sm2O3 was obtained. Upon heating, the first stage is the crystallisation of Sm2(MoO4)3, whose interaction with Sm2O3 in the second stage at 900 °C leads to the synthesis of oxymolybdate Sm2MoO6 with the scheelite structure, and this structure type is stable up to 1400 °C. The kinetic experiment in a DSC cell shows only an apparent similarity of the phase formation mechanism with a decrease of the main exoeffects by 70 °C for a mechanically activated mixture of oxides. At the same time, the study of the mechanism of phase formation by isothermal exposure at different temperatures reveals the main advantages of ceramic synthesis from an activated oxide mixture: partially mechanosynthesis of the intermediate compound Sm2(MoO4)3 takes place at room temperature; the high degree of interaction between the mechanically activated oxides allows single phase ceramics to be synthesised in a single step over a wide temperature range. The total conductivity of Sm2MoO6 with a scheelite structure, which turned out to be p-type (1 · 10−6 S/cm at 600 °C), was studied.