S.P. Sun

Environment-dependent surface structures and stabilities of SnO2 from the first principles

We have employed density functional theory to investigate the (110), (101), (100), and (001) surfaces of SnO2 within the pseudopotential, plane-wave method. Based on a thermodynamic defect model, the surface stabilities were evaluated as functions of oxygen partial pressure and temperature. Calculations showed that, below 600 K, the stoichiometric (110) has the lowest surface energy for a wide range of oxygen partial pressures, followed by the (100), (101), and (001). At higher temperatures, the stability transition from the stoichiometric to a Sn-rich termination tends to occur on all these surfaces (except the (001)) at ultrahigh vacuum. Such transitions may shift to higher pressures with increasing temperature. An equilibrium surface phase diagram was then developed to illustrate the environment dependence of these surfaces. The electronic structure of the stoichiometric (110) was also analyzed based on the electron density of states and differential charge density distribution.

The effect of point defect on mechanical properties of MoSi2

The effect of point defect on mechanical properties of MoSi2 has been investigated by the first-principles. The elastic constants, mechanical modulus, hardness and thermodynamic properties of MoSi2 with four different single point defects have been calculated. By comparing with the defect-free MoSi2, it is found that the bulk modulus/shear modulus ratio (B/G) of MoSi2 with a single point defect increases slightly while the Debye temperature decreases drastically, which indicates that MoSi2 with some point defects have relatively good ductility. The calculated three-dimensional (3D) contours of elastic modulus and these projections on the (001) and (010) planes show that the directionality of Young’s modulus and shear modulus is unapparent for MoSi2 with a point defect (VMo and MoSi) but it is relatively obvious for MoSi2 with VSi and SiMo. It suggests that VSi and SiMo can strengthen the anisotropy in elasticity. The electronic properties of C11b MoSi2 with different single point defects have been studied to reveal further the influencing mechanism of point defect on mechanical properties. This work should help reveal the interrelation between intrinsic defects and service performance of MoSi2.