Vibrational modes and structural characteristics of (Ba0.3Sr0.7)[(ZnxMg1−x)1/3Nb2/3]O3 solid solutions

Abstract

(Ba_0.3Sr_0.7)[(Zn_xMg_1−x)_1/3Nb_2/3]O₃ (BSZMN) (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solution ceramics were synthesized by the conventional solid-state sintering technique. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection spectroscopy, short for FTIR) and X-ray diffraction (XRD) were employed to evaluate the correlation between crystal structures and vibration modes of these solid solutions as a function of Mg²⁺ ions replaced by Zn²⁺ ions. It is verified that these ceramics present a phase transition, i.e., the crystal structure changes from hexagonal phase (Pm1, where x ≤ 0.4) to the pseudocubic phase (I4/mcm, where x ≥ 0.8) with increasing Zn²⁺ content. The phase transition is a gradual process, the sample where x = 0.6 is of the transition phase, i.e., at x = 0.6, phase transition begins to appear from hexagonal phase to pseudocubic phase but is not complete. The phase transition is also verified by the FTIR spectra. Tilting of oxygen octahedra is the main reason for the phase transition. The phonon modes of the vibration spectra were assigned, the position and width were determined, and the correlation of phonon vibrations with the microstructure for the different atoms substituted in B′-site was found.