Structural model for thermal expansion in MZr2P3O12 (M=Li,Na, K,Rb, Cs)

A structural model is proposed to describe the highly anisotropic thermal expansion in the sodium zirconium phosphate NaZr₂P₃O₁₂ structure as a result of the thermal motion of the polyhedra in the structure. In the proposed model the rotations of the phosphate tetrahedra are coupled to the rotation of the zirconium octahedra. Of the two versions considered, the first one allows angular distortions to occur only in the ZrO₆ octahedra; the second one permits all polyhedra to be distorted.