Browsing by Author "Ku, C. -S."

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Phase coexistence and Mn-doping effect in lead-free ferroelectric (Na1/2Bi1/2)TiO3 crystals
(2010) Tu, Chi-Shun; Huang, S.-H.; Ku, C. -S.; Lee, H.-Y.; Chien, R.R.; Schmidt, V. Hugo; Luo, H.
Phase transformations of (001)-cut (Na1/2Bi1/2)TiO3 (NBT) and 1 at. % Mn-doped NBT (Mn-NBT) crystals have been investigated by means of dielectric permittivity, conventional x-ray diffraction (XRD), and high-resolution synchrotron XRD and reciprocal space mapping. An R−R+T−T−C transition sequence was observed in NBT and Mn-NBT upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. R+T represents that the ferroelastic T phase coexists with the ferroelectric R phase. The Mn dopant can enhance dielectric response and reduce the dielectric loss in the high-temperature region due to the increased degree of ordering.
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.