Browsing by Author "Chen, H.-Y."

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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.
Poling effect and piezoelectric response in high-strain ferroelectric 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 crystal
(2010) Chen, H.-Y.; Tu, Chi-Shun; Hung, C.-M.; Chien, R.R.; Schmidt, V. Hugo; Ku, C. -S.; Lee, H.-Y.
In situ high-resolution synchrotron x-ray diffraction, dielectric permittivity, hysteresis loop, and polarization current, were used to investigate phase transitions of (211)-cut 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO30.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal before and after an electric (E)(E) field poling. A rhombohedral (R)–tetragonal (T)–cubic transition sequence was observed upon zero-field heating in both unpoled and poled samples. Before the R–T transition takes place, an extra dielectric and polarization current anomalies near 365 K were observed in the poled sample due to a transition of polarization ordering. The direct piezoelectric coefficient d33d33 exhibits a rapid increase for poling at E=1.0–1.3kV/cmE=1.0–1.3 kV/cm, followed by an overpoling behavior. The increment of polarization ordering plays an important role while the high piezoelectric response builds up.