Zhao Zongyan

The effect of cation disorder on electrical transport properties of Nd0:7(Ca, Sr, Ba)0:3MnO3

The electrical transport properties of a series of samples, Nd0.7(Ca,Sr,Ba)0.3MnO3, with a fixed average A-site cation radius rA have been studied. Infrared spectra revealed that the symmetry of the local MnO6 octahedra reduces due to the size differences between various A-site ions. From the metal transition temperature Tm up to room temperature, the variable-range-hopping conduction mechanism has been observed, and Tm exhibits a systematic decrease with increasing A-site cation disorder. In the very-low-temperature range, we have observed that resistivity increases with decreasing temperature.

The relationship of the Poynting vector and the dispersion surface in the absorbing crystal

The relationship of the Poynting vector and the dispersion surface in the absorbing crystal is studied in detail. It is found that the long-accepted concept in which the physical energy flow of waves in the absorbing crystal is normal to the real part of the dispersion surface is not valid when the contribution of the imaginary part of the atomic scattering factor to the diffraction is comparable to that of the real part.

Bragg reflection and transmission of X-rays induced by the imaginary part of the atomic scattering factor

Formulae for X-ray dynamical Bragg diffraction are derived for a plane-parallel crystal with arbitrary thickness. These formulae are applicable even when the contribution of the real part of the atomic scattering factors to the structure factor vanishes. Based on these formulae, dynamical Bragg reflection and transmission induced only by the imaginary part of the atomic scattering factor are studied in detail.