Experimental access to elastic and thermodynamic properties of RbMnFe(CN)(6).

We use spectroscopic ellipsometry to study the elastic and thermodynamic properties of the structural first-order transition of the cooperative Jahn-Teller solid, RbMn[Fe(CN)(6)]. While the analysis of the thermal dependence of the dielectric constant revealed a remarkable energy shift in the metal-to-ligand charge transfer band, that of the refractive index allowed to evaluate the volumetric thermal expansion coefficient in the two phases through the Gladstone-Dale relation. The access to the elastic properties of the solid is obtained with the reflectivity under pressure measurements, from which we estimated the bulk modulus values in the low-and high-temperature phases as B-LT=30(+/- 3) GPa and B-HT=23(+/- 2) GPa, respectively. Assuming the system is isotropic, the corresponding Debye temperature values have been found to be theta(LT)(D)(SE) similar or equal to 360(+/- 25) K and theta(HT)(D)(SE) similar or equal to 290(+/- 20) K, in good agreement with those derived from independent Mossbauer spectrometry investigations which led to theta(LT)(D)(Moss) similar or equal to 332(+/- 7) K and theta(HT)(D)(Moss) similar or equal to 280(+/- 11) K. Moreover, we have been able to extract from the SE data, the entropy change at the transition, Delta S approximate to 64 J K-1 mol(-1), which has been also found in good agreement with the value, Delta S approximate to 60 +/- 5 JK(-1) mol(-1), derived from calorimetric experiments performed in this work. (C) 2011 American Institute of Physics. [doi:10.1063/1.3528239]