Xubo Qin

Prediction of glass-forming ability of metallic liquids

We propose a concept for the prediction of the glass-forming ability (GFA) before quenching through studies of the stabilization of clusters in metallic liquids in terms of a parameter, B=dr∕dT (r is the correlation radius of clusters and T is the absolute temperature). Strong correlation between B and GFA was found for a broad range of alloy systems. When the absolute value of B is lower than 1×10−4nm∕K, the metallic liquid can be prepared into a metallic glass. This criterion is important for studies of glass-forming abilities of metallic liquids in the future.

Structure of liquid Cu–Sb alloys by ab initio molecular dynamics simulations, high temperature X-ray diffraction, and resistivity

Structure of Cu–Sb melts has been studied by ab initio molecular dynamics simulations, high-temperature X-ray diffraction and resistivity measurements. Over the whole concentration range, heterogeneous coordination numbers are larger than that of homogeneous atoms. This indicates preferential Cu–Sb coordination in Cu–Sb melts. A drop is observed in maximum position of simulated Sb–Sb partial distribution functions around Cu75Sb25, which reveals the rapid increase of Sb–Sb coordination. Around eutectic melts, main peak splitting is observed in both structure factor and simulated total pair distribution functions, which reveals the co-existence of Cu–Sb heterogeneous and Sb–Sb clusters. Abnormal changes in temperature coefficient of resistivity are observed around pure Sb and in compound-forming range, which are well interpreted as reinforcement of Peierls distortion and Cu3Sb compound clusters, respectively. Structural inhomogeneity that results from atomic size effect also has been discussed by analyzing concentration dependence of Warren–Cowley parameters and concentration correlation functions.

Damage, refractive index and near-field intensity profiles in a single-mode waveguide of LiNbO3 by 400 keV He ion implantation

We report on a single-mode waveguide in lithium niobate produced by 400?keV He ion implantation with a dose of 3 ? 1016?ions?cm?2 at liquid nitrogen temperature. Rutherford backscattering/channelling spectra have been measured in the waveguide before and after annealing and the damage profile has been extracted. The shape of the measured damage profile is similar to that of the ordinary refractive index by the intensity calculation method. The near-field intensity profile in a ridge waveguide is given and the propagation loss for the extraordinary index is estimated to be 1.9?dB?cm?1.

Structural correlations between liquid and solid Ag 70 Au 30 alloy

Through the high temperature X-ray diffraction, structural evolution of Ag<inf>70</inf>Au<inf>30</inf> alloy with varying temperatures has been investigated. The liquid alloy experiences a sudden structure change nearby 1150 °C, which has been further thermodynamically confirmed by Differential Scanning Calorimetry (DSC). Small pre-peaks have been found in the structure factor (S(Q)) curves, indicating the stable medium-range order (MRO) structure in the melt. As the temperature decreases from 1100 °C to 1000 °C, MRO structure gets more pronounced. Compared with the structures of Ag<inf>90</inf>Au<inf>10</inf>, Transmission Electron Microscope (TEM) results reveal that Ag<inf>70</inf>Au<inf>30</inf> alloy possesses much finer grains. It is concluded that there are strong correlations between melt and solid in Ag<inf>70</inf>Au<inf>30</inf> alloy, and MRO structure in the liquid favors refined solid microstructure.