Zhang Xin-Yu

Zr-Cu Amorphous Films Prepared by Magnetron Co-sputtering Deposition of Pure Zr and Cu

ZrxCu100−x amorphous films are prepared on Si (111) substrates by magnetron co-sputtering of pure Zr and Cu. It is found that the glass forming ability (GFA) of the films increases with x when x is in the range from 35 to 65 and with the best glass forming ability at x = 65. It is therefore different from the bulk counterparts, for which only x = 35 and 50 were reported to have high glass forming ability during casting. The structure of the films is sensitive to the substrate temperature and the sputtering argon pressure.

First-Principles Study of Structural Stabilities, Electronic and Optical Properties of SrF2 under High Pressure

An investigation of structural stabilities, electronic and optical properties of SrF2 under high pressure is conducted using a first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results predict that the second high-pressure phase of SrF2 is of a Ni2In-type structure, and demonstrate that the sequence of the pressure-induced phase transition of SrF2 is the fluorite structure (Fm3m) to the PbCl2-type structure (Pnma), and to the Ni2In-type phase (P63/mmc). The first and second phase transition pressures are 5.77 and 45.58 GPa, respectively. The energy gap increases initially with pressure in the Fm3m, and begins to decrease in the Pnma phases at 30 GPa. The band gap overlap metallization does not occur up to 210 GPa. The pressure effect on the optical properties is discussed.

Ab Initio Comparative Study of Zincblende and Wurtzite ZnO

By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.

Compression Behaviour of Ni77P23 Amorphous Alloy up to 30.5 GPa

The compression behaviour of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state is determined by fitting the experimental data according to the Birch–Murnaghan equation. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa. Within the pressure range from zero to the experimental one, the pressure-induced structural relaxation is reversible.

Formation and Compression Behavior of Two-Phase Bulk Metallic Glasses with a Minor Addition of Aluminum

A remarkable enhancement in room-temperature compressive deformability is realized by the minor-addition of 1.5 at.% Al in ZrTi-based bulk metallic glass. Two amorphous phases are observed by transmission electron microscopy in the Al-containing alloys and this explains the improvement of compression deformability The studies suggest that phase separation might occur in glass forming alloys with a negative enthalpy of mixing.

Effect of Yttrium Addition on Glass Forming Ability of ZrCuAlSi Alloy

The effect of yttrium addition on glass formation of a ZrCuAlSi alloy is investigated. The maximum diameter 8mm of the glassy rods for (Zr46.3Cu43.3Al8.9Si1.5)100−xYx alloy with x = 2.5 is obtained by copper mould casting. Apparent enhancement of the glass formation ability is found with addition of yttrium, mainly due to the purification of the alloy melt and the suppression of formation of the primary phases by yttrium.

Undercooling and Unidirectional Solidification of CuNi Alloy Melts

Cylinder-shaped Cu80 Ni20 alloy melt is undercooled and solidified by the combination of the electromagnetic levitation technique and the flux treatment method. Nearly constant temperature gradient of 8-10K/cm is realized for the cylindrical melts with different undercooling levels at the bottom ends. The experimental results reveal that with the increase of the undercooling of the melts from 35 to 220K, the microstructures undergo transition from coarse dendrites to granular grains, unidirectional dendrites, and finally to equiaxed grains.

Electrochemical Behavior of Tungsten in the (NaCl-KCl-NaF-Na2WO4) Molten Salt

Abstract The electrochemical reaction mechanism and the electrocrystallization process of tungsten in the NaCl-KCl-NaF-Na2WO4 molten salt were investigated at 973 K (700 °C) by means of cyclic voltammetry, chronopotentiometry and chronoamperometry technique. The results show that the electrochemical reaction process of tungsten is a quasi-reversible process mix-controlled by ion diffusion rate and electron transport rate; the electrocrystallization process of tungsten is an instantaneous hemispheroid three-dimensional nucleation process; the tungsten ion diffusion coefficient is 2.543×10−5cm·s−1 at the experimental condition of XNaCl:XKCl:XNaF: XNa2WO4= 2:2:1:0.01.

Voronoi Structural Evolution of Bulk Silicon upon Melting

The Voronoi structural evolution of silicon upon melting is investigated using a molecular dynamics simulation. At temperatures below the melting point, the solid state system is identified to have a four-fold coordination structure 〈4,0,0,0〉. As the temperature increases, the five-fold coordination 〈2,3,0,0〉 and six-fold coordination structures 〈2,2,2,0〉 and 〈0,6,0,0〉 are observed. This is explained in terms of increasing atomic displacement due to thermal motion and the trapping of the moving atoms by others. At temperatures above the melting point, nearly all of the four-fold coordination structures grows into multiple-fold coordination ones.

The structural, elastic, and electronic properties of ZrxNb1?xC alloys from first principle calculations

The structural, elastic, electronic, and thermodynamic properties of ZrxNb1−xC alloys are investigated using the first principles method based on the density functional theory. The results show that the structural properties of ZrxNb1−xC alloys vary continuously with the increase of Zr composition. The alloy possesses both the highest shear modulus (215 GPa) and a higher bulk modulus (294 GPa), with a Zr composition of 0.21. Meanwhile, the Zr0.21 Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states. In addition, the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing.