Time-of-flight neutron powder diffraction and specific heat measurements were used to study the nature of thermal expansion in rhenium trioxide, an electrically conducting oxide with cubic symmetry. The temperature evolution of the lattice parameters show that ReO3 can exhibit negative thermal expansion at low temperatures and that the transition from negative to positive thermal expansion depends on sample preparation; the single crystal sample demonstrated the highest transition temperature, 300 K, and largest negative value for the coefficient of thermal expansion, alpha = -1.1(1)x 10^-6 K^-1. For the oxygen atoms, the atomic displacement parameters are strongly anisotropic even at 15 K, indicative of a large contribution of static disorder to the displacement parameters. Further inspection of the temperature evolution of the oxygen displacement parameters for different samples reveals that the static disorder contribution is greater for the samples with diminished NTE behavior. In addition, specific heat measurements show that ReO3 lacks the low energy Einstein-type modes seen in other negative thermal expansion oxides such as ZrW2O8.
Convergent beam electron-diffraction investigation of lattice mismatch and static disorder in GaAs/GaAs1-xNx intercalated GaAs/GaAs1-xNx:H heterostructures
Calculated effects of disorder on the Mo core levels in purple bronze Li$_2$Mo$_{12}$O$_{34}$
用从头算DFT-LMTO方法计算了有序和热无序Li $_2$ Mo $_{12}$ O $_{34}$的能带结构，重点研究了Mo 3d芯能级的行为.结果表明，热无序和零点运动导致大量的核心水平加宽，并在室温下的加宽被预测为足够大于在零度下，以允许通过XPS测量检测。然而，真正的紫青铜有10%的Li空位，静态无序将减弱$T$依赖的加宽。有人认为，芯级光谱可以是一个有用的工具，用于测量在许多材料中的热无序，特别是对于那些轻微的静态无序。磁性材料芯能级的研究将有助于理解$T$依赖的自旋矩。
