Point Defect Characteristics of High-$k$ Double Rare-Earth-Doped BaTiO3 Ceramics with Diffuse Phase Transition by Electron Spin Resonance

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The temperature dependence of the electron spin resonance (ESR) signals of high-$k$ (Ba1-xLax)(Ti1-x/4-0.05Ce0.05)O3 ceramics (BLTC, $x = 0.01--0.05$), showing a strong diffuse phase transition (DPT) behavior, were examined by the powder ESR technique. Undoped BaTiO3 (BT) and (Ba1-xLax)Ti1-x/4O3 (BL4T, $x = 0.04$), both of which show a first-order phase transition (FPT), and Ba(Ti1-yCey)O3 (BTC5, $y = 0.05$) ceramics with DPT, were also investigated with ESR for comparison. A signal with $g = 1.974$, which is associated with the intrinsic point defect (V$''_{\text{Ba}}$) in BT, disappeared in both BLTC and BL4T; whereas, the signal with $g = 2.004$ was activated markedly and moderately when $T > T_{\text{C}}$ (the Curie point) for BT and BL4T, respectively. BLTC and BL4T ceramics show only a signal with $g = 2.004$, indexed as Ti-vacancy defects (V$_{\text{Ti}}''''$). The signal intensity being nearly independent of temperature and La content (except for $x = 0.01$) is a characteristic of point defects in BLTC with DPT and provides the evidence that Ti vacancies are the predominant compensation mode in BLTC.
2009-02-25