Synthesis,Characterization, and Chemical Vapor Transport of Solid Solutions in the MgMoO4‐NiMoO4 System

Two solid solution series exist in the system MgMoO₄‐NiMoO₄. The α‐Ni_1–yMg_yMoO₄ solution series, isostructural to α‐NiMoO₄, is thermodynamically stable at ambient conditions for compositions between 0 % and about 75 % magnesium content. The solution series β‐Mg_1–xNi_xMoO₄, isostructural to MgMoO₄ and the high temperature β modification of NiMoO₄, is thermodynamically stable at ambient conditions for compositions with < 25 % nickel content. A complete solid solution series β‐Mg_1–xNi_xMoO₄ exists at higher temperatures (> 823 K). The transition temperature for the α → β transition decreases with increasing magnesium content. The coexistence of both polymorphs at room temperature in samples with a wide range of composition is a result of the kinetic inhibition of the phase transition β → α. The chemical vapor transport of β‐Mg_1–xNi_xMoO₄ solid solutions with chlorine was investigated. Crystals with a nickel content up to 25 % were synthesized in temperature gradients 1273 K → 1223 K or 1273 K → 1173 K. Deposited nickel richer crystals are destroyed during cooling down to room temperature due to the phase transition. The observed distinctive nickel enrichment during the transport process is in good agreement with predictions by thermodynamic modeling.