Temperature‐dependent Raman scattering studies of Na2MoO4

The mode assignment of the cubic phase of anhydrous Na₂MoO₄ was carried out on the basis of lattice dynamic calculation using the classical rigid‐ion model. Temperature‐dependent studies indicate that this crystal remains in the cubic structure in the 15–773 K range and undergoes a phase transition at around 783 K. The behavior of the Raman modes indicates that this transition is strongly first‐order in nature and the phase above 773 K may have an orthorhombic symmetry. This transition is connected with tilting and/or rotations of the MoO₄ tetrahedra, which lead to a disorder at the MoO₄ sites. Our results give also evidence that the Mo O bond lengths decrease in the high‐temperature phase. Copyright © 2008 John Wiley & Sons, Ltd.