Dielectric stability in the relaxor: Na₀.₅Bi₀.₅TiO₃-Ba₀.₈Ca₀.₂TiO₃-Bi(Mg₀.₅Ti₀.₅)O₃- NaNbO₃ ceramic system

Ceramics with temperature-stable dielectric characteristics have been developed in the system: 0.6[0.85Na0.5Bi0.5TiO3-(0.15-x)Ba0.8Ca0.2TiO3-xBi(Mg0.5Ti0.5)O3]−0.4NaNbO3, x ≤ 0.15. Dielectric measurements exhibited relaxor ferroelectric characteristics with temperature-stable relative permittivity from εr~1330 ± 15% in the temperature range from −70 °C – 215 °C and tanδ ≤ 0.02 from −20 °C to 380 °C for x = 0 compositions. For the Bi(Mg0.5Ti0.5)O3 modified compositions the temperature range of stable relative permittivity extended from −70 °C to 400 °C, with εr ~ 950 ± 15% and tanδ ≤ 0.02 from −70 °C to 260 °C. Values of dc resistivity were ~ 108 Ω m at a temperature of 300 °C and the corresponding RC constant values were in the range from 0.40 − 0.78 s at 300 °C. All ceramic samples exhibited a linear polarisation-electric field response at maximum applied electric field of 5 kV/cm (1 kHz)

Insight into an atomic arrangement of [KNbO3]0.9 – [BaNi0.5Nb0.5O3]0.1 powder formed at various calcination temperatures by X-ray absorption spectroscopy

Lead-free [KNbO3]0.9 – [BaNi0.5Nb0.5O3]0.1 (KBNNO) perovskite powders are synthesized by the solid-state combustion technique. Phase identification and the crystal structure change at various calcination temperatures Tcal are carried out by X-ray diffraction (XRD) technique. Local structure distortion is studied by X-ray absorption spectroscopy (XAS) for revealing X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XRD result shows that the structure of KBNNO changes from pseudo-cubic to weakly tetragonal structure when the calcination temperature increases. The extracted parameters from Nb L3-edge and K K-edge XANES signals show that the KBNNO structure formed at high Tcal (≥750 °C) has an orthorhombic structure. In addition, the fitted EXAFS spectra indicate a decrease of interatomic distances for three shells when Tcal increases. The obtained structural distortion difference from XRD and XAS can be explained by the fact that XRD signal is from all atoms in the unit cell, while XAS can specifically probe the local structure of specific atoms in the unit cell. Keywords: A. Ferroelectrics, B. Solid state reaction, C. Atomic scale structure, C. Phase transition, D. Synchrotron radiation, D. X-ray diffractio