Tunable Thermal Expansion from Negative, Zero, to Positive in Cubic Prussian Blue Analogues of GaFe(CN)6

The achievement of controlling thermal expansion is important for open-framework structures. The present work proposes a feasible way to adjust the coefficient of thermal expansion continuously from negative to positive via inserting guest Na+ ions or H2O molecules into a GaFe(CN)6 framework. The guest ions or molecules have an intense dampening effect on the transverse vibrations of CN atoms in the -Ga-N≡C-Fe- linkage, especially for the N atoms. This study demonstrates that electrochemical or redox intercalation of guest ions will be an effective way to tune thermal expansion in those negative thermal expansion open-framework materials induced by low-frequency phonons.