Thermal expansion in Prussian Blue analogs M3[Cr(CN)6]2.nH2O (M = Mn Fe, Co, Ni)

Thermal expansion in Prussian Blue Analogs (PBAs) M-3[Cr(CN)(6)](2).nH(2)O (M = Mn, Fe, Co, Ni; n = 10-16) was studied using powder X-ray diffraction (XRD) as a function of temperature in the range 123-298 K. Standard chemical precipitation was used to prepare the materials and they were characterized using standard characterization techniques XRD, X-ray fluorescence (XRF), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. All materials were found to crystallize in the cubic structure with space group Fm (3) over barm. Strong compositional dependence of thermal expansion is found in this series of PBAs. While Mn-3[Cr(CN)(6)](2).12H(2)O and Ni-3[Cr(CN)(6)](2).16H(2)O show positive thermal expansion (PTE) behavior the other two PBAs, Fe-3[Cr(CN)(6)](2).10H(2)O and Co-3[Cr(CN)(6)](2).14H(2)O, show strong negative thermal expansion (NTE) behavior with as large coefficient of thermal expansion (CTE) as -19.7 x 10(-6) K-1 (for M = Fe) in the temperature range 123-223 K. For the PBAs showing NTE, the magnitude of NTE coefficients can be correlated with the trends for M cation size and cell (or lattice) parameter.