Thermal Behavior of Alkali Zinc Phosphates

Alkali zinc phosphates Na2ZnP2O7, K2ZnP2O7, LiNaZnP2O7, LiKZnP2O7, NaKZnP2O7, and Li12Zn4(P2O7)5, which can be prepared both by the solid-phase synthesis and through crystallization from a glass, are studied using high-temperature X-ray powder diffraction. The unit cell parameters as functions of the temperature in the range 20–700°C are analyzed, and the linear anisotropic thermal expansion coefficients are determined. The majority of these compounds are characterized by strong anisotropy of thermal expansion. It is found that the LiKZnP2O7 compound exists in two polymorphic modifications, namely, the low-temperature monoclinic modification and the high-temperature orthorhombic modification.