Browsing by Author "Yang, W.-C."
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Item 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.Item Origins of dielectric response and conductivity in (Bi1-xNdx)FeO3 multiferroic ceramics(2011) Tu, Chi-Shun; Yang, W.-C.; Schmidt, V. Hugo; Chien, R.R.The dielectric response and conductivity have been measured in (Bi1−x Nd x )FeO3 (x = 0.0 and 0.05) ceramics as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers, B (in temperature units), every lattice constant, a, and extrinsic barriers, B + Δ, every distance, d, is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and step-like dielectric relaxation in the region of 500–800 K. Good qualitative fits of dielectric dispersion and conductivity are obtained with d = 20–30 nm, B = 8400–8700 K (∼0.72–0.75 eV), and Δ = 2500 K (∼0.215 eV). The resistivity plot of scaled ρ" versus ρ' indicates a contribution of grain boundaries or internal defects to the conductivity.