Abstract: | 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. |