Crystal structure and thermal properties of the LixNa1–xKZnP2O7 solid solutions and its relation to the MM′ZnP2O7 diphosphate family

Abstract New solid solutions of Li x Na 1 –x KZnP 2 O 7, belonging to the MM’ ZnP 2 O 7 structural family ( M  = Li + , Na + , Zn 2+ ; M’  = Na + , K + ), were prepared and phase equilibria along the LiKZnP 2 O 7 –NaKZnP 2 O 7 section were reported. These solid solutions were investigated single-crystal X-ray diffraction, high-temperature X-ray powder diffraction (HTXRD), differential scanning calorimetry, and impedance spectroscopy. A miscibility gap was found within the range of 0.8  x x Na 1 –x KZnP 2 O 7 solid solutions is revealed: increasing the radius of the metal by 0.01 A leads to the same deformations of the crystal structure as increasing the temperature by 31 °C. The Li/Na↔Zn cation exchange lead to an increase in conductivity above 300 °C. The alkali mixed effect in activation energy occurs for Li x Na 1– x KZnP 2 O 7 solid solutions near x  = 0.5. The phase with the 2 a ×2 b × c superstructure ordering was observed as a result of the solid solution melting.