The rich crystal chemistry of the AMM′(PO4)2 morphotropic series: NaZnAl(PO4)2, the first Na representative with a new structure type

A novel phosphate, sodium zinc aluminium bis(phosphate), NaZnAl(PO₄)₂, was obtained under mild‐temperature hydrothermal conditions at 553 K. The crystal structure has been studied using single‐crystal X‐ray experimental data. The pseudo‐hexagonal phase NaZnAl(PO₄)₂ crystallizes in the monoclinic space group P2₁/c. Its unique crystal structure is based on a three‐dimensional (3D) framework built by Zn‐, Al‐ and P‐centred tetrahedra sharing vertices. Channels parallel to the 101] and 01] directions are limited by six‐ and eight‐membered windows, and incorporate Na atoms. The new compound is discussed as a member of the morphotropic series AMM′PO₄, where A = Na, K, Rb or NH₄, M = Cu, Ni, Co, Fe, Zn or Mg and M′ = Fe, Al or Ga. The title compound is the first Na representative within the series and is characterized by a 3D architecture of tetrahedra populated in an ordered manner by Zn²⁺, Al³⁺ and P⁵⁺ ions.