Determinación del factor F libre de retroceso Mössbauer de las ortoferritas de tierras raras ReFeO3 (Rare-earth=La, Pr, Nd, Sm) sintetizadas por el método de auto-combustión.

The rare-earth orthoferrites compounds REFeO_3 (Ln= La, Pr, Nd, Sm) were synthesized by self-combustion method (glycine-nitrate process). Their phases were characterized by X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Their thermal stability was studied with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mössbauer spectra of Fe57 without an extern field show similar hyperfine interactions for equivalent crystallographic Fe(III)6 sites. The chromic behavior of these compounds was studied by measurements of diffuse reflectance under photo, thermal and electric stimulus. Using the CIELab coordinates to calculate &ñ8710;E a thermochromic effect is appreciable for the human eye in the three different ranges of temperature measured. Applying Kubelka-Munk equation was obtained the absorbance spectra and with linear adjustment the optical gaps were calculated.