Structural and ferroelectric phase evolution in [KNbO3]1−x[BaNi1/2Nb1/2O3−δ]x (x=0,0.1)

Abstract

The phase transition evolution for ${[{\mathrm{KNbO}}_{3}]}_{1\ensuremath{-}x}{[{\mathrm{BaNi}}_{1/2}{\mathrm{Nb}}_{1/2}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}]}_{x}\phantom{\rule{0.16em}{0ex}}(x=0,0.1)$ is determined via complementary dielectric permittivity and Raman-scattering measurements. Raman scattering by optical phonons over the range of 100--$1000{\mathrm{cm}}^{\ensuremath{-}1}$ for 83 K $lTl873$ K reveals six discernible zone-center optical phonon modes. Mode behaviors are observed through structural and ferroelectric phases in the solid solution $x=0.1$ and compared with those for end member $x=0$ and with the results of temperature-dependent dielectric permittivity. Rigorous peak fitting analyses of spectra collected from the solid solution and end member indicate structural and ferroelectric phase transition temperatures that are close to those for the ${\mathrm{KNbO}}_{3}$ end member despite the inclusion of 5 atomic % of ferroelectrically inactive Ni cations. Density functional theory calculations were performed in the solid solution and end member using both cation displacement and Berry phase-based methods. Differences in the electronic and polar properties between the solid solution and the end member highlights local and nonlocal characteristics, which are discussed in relation to the experimental data.