Tunable Thermal Expansion from Negative, Zero, to Positive in Cubic Prussian Blue Analogues of GaFe(CN) 6
The control of thermal expansion of open framework Prussian blue analogues is vital but remains challenging. The present work proposes an effective method to control the thermal expansion, in which guest ions (Na + ) and molecules (H 2 O) can adjust the coeffecient of thermal expansion from strong negative, to near zero, to positive in GaFe(CN) 6 Prussian blue analogues. Direct experimental evidence by high resolution synchrotron X-ray diffraction and X-ray absorption fine structure shows that the guest ions or molecules have intense dampening effect on the transverse vibrations of -Ga–N≡C–Fe– linkage responsible for NTE, especially for N atoms. The role of guests in controlling thermal expansion is attributed to the strong interaction of local environment – steric dampening. Furthermore, the present study demonstrates that electrochemical or redox intercalation of guest ions can be a general and effective method for controlling thermal expansion for those open framework materials with negative thermal expansion driven by low Frequency phonons.