Raman Spectroscopy of (Ba_1-xSr_x)(Mg_1/3Nb_2/3)O₃Solid Solutions from Microwave-Hydrothermal Powders

Microwave-hydrothermal synthesis was employed to produce crystalline, single-phase Ba(Mg 1/3 Nb 2/3 )O 3 and Sr(Mg 1/3 Nb 2/3 )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 (Ba 1- x Sr x )(Mg 1/3 Nb 2/3 )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 to monoclinic . Lorentzian lines were used to fit the spectra obtained at low temperatures, which present 35 bands for the Sr(Mg 1/ 3 Nb 2/3 )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.