Estudo do espectro de Fônons das Perovskitas A2NiB''O6 (A = Sr, Ba; B'' = W, Mo) em função da temperatura

Abstract

In recent years, the scientific community dedicated to the study in the field of condensed matter physics has been dedicated to the study of materials of the perovskite oxide type due to its recognized technological potential. The study of its structural and vibrational properties have been made by several techniques, such as X-ray Diffraction and Neutrons and Raman and Infrared spectroscopies, which are very sensitive to the structural changes of these materials. This work presents a study of the behavior of the phonons as a function of temperature, in the range of 10 K to 300 K, of the double perovskites A2NiB

′′O6 (A = Sr, Ba and B

′′ = W, Nb), by means of Raman spectroscopy technique. It is known that, at room temperature, Strontium-containing compounds crystallize into a tetragonal structure with I4/m space group and those containing Barium crystallize into a cubic structure with space group Fm3̅m. Based on this, the Raman spectra at room temperature were interpreted by means of the factor group analysis in terms of the respective space groups, where for the first time the unfolding of the doubly (Eg) and triple (T2g) degenerated phonons for the tetragonal structure, which presents slight distortion with respect to the cubic one. The Raman spectra as a function of temperature presented strong evidence of spin-phonon coupling when analyzed in the temperature range in which the magnetic order of these perovskites occurs (T = 70 K for Ba2NiWO6, T = 50 K for Ba2NiMoO6, T = 59 K for Sr2NiWO6 and T = 81 K for Sr2NiMoO6).