Browsing by Author "Anthoninappen, J."

Now showing 1 - 3 of 3

Calcium-doping effects on photovoltaic response and structure in multiferroic BiFeO3 ceramics
(2013) Tu, Chi-Shun; Hung, C.-M.; Xu, Zhe-Rui; Schmidt, V. Hugo; Ting, Yi; Chien, R.R.; Peng, Y.-T.; Anthoninappen, J.
Photovoltaic (PV) effects, power-conversion efficiencies, and structures have been systematically measured in (Bi1− x Ca x )FeO3−δ ceramics for x = 0.05, 0.10, and 0.15. The heterostructures of indium tin oxide (ITO) film/(Bi1− x Ca x )FeO3−δ ceramics/Au film exhibit significant PV effects under illumination of λ = 405 nm. The maximum power-conversion efficiency in the ITO/(Bi0.90Ca0.10)FeO2.95 (BFO10C)/Au can reach 0.0072%, which is larger than 0.0025% observed in the graphene/polycrystalline BFO/Pt films [Zang et al., Appl. Phys. Lett. 99, 132904 (2011)]. A theoretical model based on optically excited current in the depletion region between ITO film and Ca-doped BFO ceramics is used to describe the I-V characteristic, open-circuit voltage, and short-circuit current density as a function of illumination intensity. This work suggests that the Ca-substitution can reduce the rhombohedral distortion and stabilize the single-phase structure.
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.
The origin of photovoltaic responses in BiFeO3 multiferroic ceramics
(2012) Tu, Chi-Shun; Hung, C.-M.; Schmidt, V. Hugo; Chien, R. R.; Jiang, M.-D.; Anthoninappen, J.
Multiferroic BiFeO3 (BFO) ceramics with electrodes of indium tin oxide (ITO) and Au thin films exhibit significant photovoltaic effects under near-ultraviolet illumination (λ = 405 nm) and show strong dependences on light wavelength, illumination intensity, and sample thickness. The correlation between photovoltaic responses and illumination intensity can be attributed to photo-excited and thermally generated charge carriers in the interface depletion region between BFO ceramic and ITO thin film. A theoretical model is developed to describe the open-circuit photovoltage and short-circuit photocurrent density as a function of illumination intensity. This model can be applied to the photovoltaic effects in p–n junction type BFO thin films and other systems. The BFO ceramic exhibits stronger photovoltaic responses than the ferroelectric Pb1−xLax(ZryTi1−y)1−x/4O3 (PLZT) ceramics under near-ultraviolet illumination. Comparisons are made with other systems and models for the photovoltaic effect.