Browsing by Author "Wang, S.-F."

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Dielectric properties in lead-free piezoelectric (Bi0.5Na0.5)TiO3-BaTiO3 single crystals and ceramics
(2014) Chen, Cheng-Sao; Tu, Chi-Shun; Chen, Pin-Yi; Ting, Yi; Chiu, S.-J.; Hung, C.-M.; Lee, H.-Y.; Wang, S.-F.; Anthoninappen, J.; Schmidt, V. Hugo; Chien, R. R.
The 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 (BNB7T) piezoelectric single crystals and ceramics have been grown respectively by using the self-flux and solid-state-reaction methods. The real (ε′) and imaginary (ε″) parts of the dielectric permittivity of BNB7T crystals and ceramics were investigated with and without an electric (E) poling as functions of temperature and frequency. The BNB7T crystal shows a stronger dielectric maximum at Tm~240 °C than the ceramic at Tm~300 °C. The dielectric permittivity of BNB7T ceramic shows an extra peak after poling at an electric field E=40 kV/cm in the region of 80–100 °C designated as the depolarization temperature (Td). A wide-range dielectric thermal hysteresis was observed in BNB7T crystal and ceramic, suggesting a first-order-like phase transition. The dielectric permittivity ε′ obeys the Curie–Weiss equation, ε′=C/(T−To), above 500 °C, which is considered as the Burns temperature (TB), below which polar nanoregions begin to develop and attenuate dielectric responses.
Structural stability and depolarization of manganese-doped (Bi 0.5 Na 0.5 ) 1-x Ba x TiO 3 relaxor ferroelectrics
(2014-10) Wang, S.-F.; Tu, Chi-Shun; Chang, T.-L.; Chen, Pin-Yi; Chen, Cheng-Sao; Schmidt, V. Hugo; Anthoniappen, J.
This work reveals that 0.5 mol. % manganese (Mn) doping in (Bi0.5Na0.5)1−xBaxTiO3 (x = 0 and 0.075) solid solutions can increase structural thermal stability, depolarization temperature (Td), piezoelectric coefficient (d33), and electromechanical coupling factor (kt). High-resolution X-ray diffraction and transmission electron microscopy reveal coexistence of rhombohedral (R) R3c and tetragonal (T) P4bm phases in (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) and 0.5 mol. % Mn-doped BN7.5BT (BN7.5BT-0.5Mn). (Bi0.5Na0.5)TiO3 (BNT) and BN7.5BT show an R − R + T phase transition, which does not occur in 0.5 mol. % Mn-doped BNT (BNT-0.5Mn) and BN7.5BT-0.5Mn. Dielectric permittivity (ε′) follows the Curie-Weiss equation, ε′ = C/(T − To), above the Burns temperature (TB), below which polar nanoregions begin to develop. The direct piezoelectric coefficient (d33) and electromechanical coupling factor (kt) of BN7.5BT-0.5Mn reach 190 pC/N and 47%.