Correlation of crystal structure, dielectric properties and lattice vibration spectra of (Ba1−xSrx)(Zn1/3Nb2/3)O3 solid solutions

Abstract

(Ba_1−xSr_x)(Zn_1/3Nb_2/3)O₃ (BSZN) (x = 0.0, 0.50, 0.60, 0.65, 0.70, 1.0) solid solutions were synthesized by a conventional solid-state sintering technique. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection spectroscopy, FTIR) and X-ray diffraction (XRD) were employed to evaluate the crystal structures and phonon modes of these solid solutions. Dielectric constants (ε_r) and temperature coefficient of capacitances (τ_c) were examined to reveal the correlation of the dielectric properties and the crystal structures. The results show that with the increase in Sr²⁺ content, the lattice structures of ceramics turn gradually from disordered cubic structure to ordered structure because antiphase tilting of the oxygen octahedra occurs where x ≥ 0.65, which is the main reason for the phase transitions and variation of crystal structure. The appearance of the phase transitions is associated with variation of the symmetry structure, from cubic (Pmm, where x = 0) to pseudocubic (I4/mcm, where 0.65 ≤ x < 1.0) and then to hexagonal (Pml, where x = 1.0). New phonon modes appear at around 250 cm⁻¹ in Raman spectra where x ≥ 0.65, and there is also a different phonon mode appearing at 156 cm⁻¹ in the FTIR spectra at the same x range. The appearance of the new phonon modes is the characteristic of ceramics whose oxygen octahedra have tilted with Sr²⁺ concentration where x ≥ 0.65. The Raman shifts are related to the rigidity of the oxygen octahedra, while the widths of peaks are correlated with τ_c. The FTIR spectra were subjected to the Kramers–Kronig analysis, and the imaginary part of the dielectric constant was analyzed in detail.