A thermodynamic free energy function in the form of an eighth-order polynomial has been developed for bulk potassium niobate KNbO3, based on the Landau-Ginsburg-Devonshire phenomenological theory. The obtained free energy function successfully models the ferroelectricsingle domain intrinsic properties of KNbO3, including the three sequential phase transition temperatures as well as polarizations, dielectric constants, and lattice constants along the whole ferroelectric temperature range. It is applicable to explaining and predicting the extrinsic contributions such as hydrostatic pressure on the bulks properties and substrate constraints on the thin films properties.

We have investigated the effects of O on the structure and mechanical properties of NiAl intermetallics using a first-principles pseudopotential total-energy method based on the density functional theory with the generalized gradient approximation. We found that the impurity O atom can either replace Ni atom or go into the tetrahedron interstitial site depending on the surrounding environment. In both cases, O tends to form an Al2O3-like tetrahedron structure with its nearest Al or Ni atoms, leading to the formation of the stronger O-Al bond containing covalent component. We demonstrate that the presence of O will cause an increase of the brittleness and a decrease of the ductility of NiAl based on the calculated elastic constants and the empirical criterions for both substitutional and interstitial cases. Our calculations provide a way to suppress the negative effect of O by adding the alloying element with lower electronegativity than that of Al.

Using a first-principles method, we have investigated structure, stability and diffusion of hydrogen (H) in tungsten (W). We found that single H atom prefers to occupy the tetrahedral interstitial site with the formation energy of～-2.45 eV. Two H in the tetrahedral interstitial sites form a pairing cluster along the <110> directions with the H–H distance of ～2.22, while the corresponding binding energy is only 0.02 eV, indicating a very weak attractive interaction. This suggests that H itself is not capable of trapping other H atoms to form a H2 molecule. The kinetics of H in intrinsic W is discussed, and the diffusion barrier of H that jumps between the tetrahedral interstitials is calculated to be 0.20 eV.

采用第一原理方法，计算了Pb掺杂锐钛矿型TiO2的晶胞几何结构和电子结构。由于Pb的原子半径大于Ti，掺Pb后晶胞体积明显增大；水平方向和顶点方向的Pb-O键键长比相应的Ti-O键键长增长。由于Pb与O原子的sp轨道杂化作用，与Pb近邻的O原子p电子态出现尖锐的峰，并使处于第一价带的p电子态的带宽由4.6eV增至7.3eV；同时O的p轨道产生空态，掺杂后系统的导带底由Pb的p轨道构成。Pb掺杂使得锐钛矿型TiO2的能隙大幅度减小，因此，可以通过掺杂Pb实现对于锐钛矿型TiO2的能带调制，从而改变TiO2的光催化性能。计算结果与实验趋势相符

采用基于密度泛函理论和局域密度近似的第一性原理赝势方法，计算了纯Al晶界和杂质Sr偏析Al晶界的原子结构和电子结构, 结果表明Sr偏析引起了晶界膨胀和晶界处电子密度的大幅度降低，从而导致晶界结合力的减弱, 这应为Sr杂质偏析引起的Al晶界脆化的主要根源所在。