First principles calculation of a large variation in dielectric tensor through the spin crossover in the CsFe[Cr(CN)6] Prussian blue analogue

The dielectric response of spin-crossover (SCO) materials is a key property facilitating their use in next-generation information processing technologies. Solid state hybrid density functional theory calculations show that the temperature-induced and strongly hysteretic SCO transition in the Cs+Fe2+[Cr3+(CN-)(6)] Prussian blue analogue (PBA) is associated with a large change (Delta) in both the static, Delta epsilon(0)(HS - LS), and high frequency, Delta epsilon(infinity)(HS - LS) dielectric constants. The SCO-induced variation in CsFe[Cr(CN)(6)] is significantly greater than the experimental Delta epsilon values observed previously in other SCO materials. The phonon contribution, Delta epsilon(phon)(HS - LS), determined within a lattice dynamics approach, dominates over the clamped nuclei term, Delta epsilon(infinity)(HS - LS), and is in turn dominated by the low-frequency translational motions of Cs+ cations within the cubic voids of the Fe[Cr(CN)(6)](-) framework. The Cs+ translational modes couple strongly to the large unit cell volume change occurring through the SCO transition. PBAs and associated metal-organic frameworks emerge as a potentially fruitful class of materials in which to search for SCO transitions associated with large changes in dielectric response and other macroscopic properties. (C) 2014 AIP Publishing LLC.