Browsing by Author "Yao, Y.-D."

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Dielectric permittivity and magnetoelectric coupling in multiferroic BiFeO3 and (Bi0.95La0.05)FeO3 ceramics
(2011) Tu, Chi-Shun; Ding, Y.; Yang, W.-C.; Wang, T.-H.; Chien, R. R.; Schmidt, V. Hugo; Yao, Y.-D.; Wu, K.-T.
Dielectric permittivity and loss of BiFeO 3 (BFO) and 5 mol% lanthanum-substituted BFO [(Bi 0.95 La 0.05 )FeO 3 or BFO-5% La] ceramics have been carried out as functions of temperature and frequency. A frequency-dependent and broad dielectric shoulder and maximum were observed in BFO and BFO-5% La near 600-700 K. These dielectric responses are likely due to the magnetoelectric coupling while the antiferromagnetic-paramagnetic transition takes place near the Néel temperature. As an approximation, a barrier model with intrinsic barriers B (in temperature unit) every lattice constant a and extrinsic barriers B +Δ every distance d is introduced to describe the low-frequency upturn in dielectric loss in the high-temperature region. Good qualitative fits are obtained for BFO and BFO-5% La. This work suggests that 5 mol% La substitution can enhance dielectric response and considerably reduce electric conductivity.
Magnetoelectric coupling and phase transition in BiFeO3 and (BiFeO3)0.95(BaTiO3)0.05 ceramics
(2011) Wang, T.-H.; Tu, Chi-Shun; Chen, H.-Y.; Ding, Y.; Lin, T.C.; Yao, Y.-D.; Schmidt, V. Hugo; Wu, K.-T.
In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle α R (associated with an inflection in the lattice constantaR ) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.