Wei-Guo Yin

Dielectric permittivity and electric modulus in Bi2Ti4O11

Frequency and temperature dependences of dielectric permittivity and electric modulus of pure and Ba-doped Bi2Ti4O11 were studied in the ranges of 10−1–106 Hz and −150–350 °C, respectively. We found that the antiferroelectric phase transition temperature of Bi2Ti4O11 decreases with Ba doping. In the permittivity studies, we also observed dielectric relaxation peaks shift to higher temperature with increasing frequency. Furthermore, in the electric modulus formalism, conducting peaks were uncovered above 150 °C in addition to the dielectric relaxation peak. We discussed the mechanisms for the dielectric relaxation and conduction processes based on TiO6 octahedra distortion and a space-charge model.

Molecular Dynamics Simulation of the Order-Disorder Phase Transition in Solid NaNO 2

We present molecular dynamics simulations of solid NaNO 2 using pair potentials with the rigid-ion model. The crystal potential surface is calculated by using an a priori method which integrates the ab initio calculationswith the Gordon-Kim electron gas theory. This approach is carefully examined by using different population analysis methods and comparing the intermolecular interactions resulting from this approach with those from the ab initio Hartree-Fock calculations. Our numerics show that the ferroelectric-paraelectric phase transition in solid NaNO 2 is triggered by rotation of the nitrite ions around the crystallographical c axis, in agreement with recent x-ray experiments [Gohda et al., Phys. Rev. B 63, 14101 (2000)]. The crystal-field effects on the nitrite ion are also addressed. An internal charge-transfer effect is found.

Theoretical study on the optical properties of polyvinylidene fluoride crystal

We report our first-principles studies on the linear and non-linear optical properties of ferroelectric polyvinylidene fluoride crystal. Calculated values of the refractive indices agree well with experiments. As regards the second-harmonic-generation coefficients, theoretical values are larger than experimental ones. Possible reasons for the discrepancy are discussed.

HYBRIDIZATION BETWEEN 4f-5d STATES IN ErAs(100)

Generally in both elemental and compound rare earth systems, the 4f levels are treated as core states with little interaction with the 5d hybrid conduction and valence band states. In the present study, the band dispersions of the rare-earth pnictide erbium arsenide (ErAs) are observed to be perturbed from this expectation. Both photoemission symmetry selection rules and ab initio calculations provide evidences of the 4f-5d hybridization. This finding is also supported by the f–f resonant transition excitation energy shifts in characteristic electron-energy-loss spectroscopy (EELS).