Raman spectroscopy of (Ba1-xSrx)(Mg1/3Nb2/3)O3 solid solutions from microwave-hydrothermal powders

Microwave-hydrothermal synthesis was employed to produce crystalline, single-phase Ba(Mg1/3Nb2/3)O-3 and Sr(Mg1/3Nb2/3)O-3 powders for the first time. The ceramics were mixed and fired at high temperatures to achieve ordered solid solutions. X-ray diffraction and Raman spectroscopy were employed to evaluate the crystal structure and phonon modes of chemically substituted (Ba1-xSrx)(Mg1/3Nb2/3)O-3 (x = 0.0, 0.3, 0.5, 0.7, 0.9, 1.0) microwave ceramics. It was verified that these materials present a phase transition for Sr-rich samples (x >= 0.7), from trigonal D-3d(3) to monoclinic C-2h(3). Lorentzian lines were used to fit the spectra obtained at low temperatures, which present 35 bands for the Sr(Mg1/3Nb2/3)O-3 ceramic. The position and width of the phonon modes were determined and correlated to the ionic radii, mass, and tolerance factors for the different atoms substituted in the A-site.