Qin Xiaoying

Strongly Correlated Effect in TiS2

The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation (GGA) as well as the on-site Coulomb interaction correction (+U). The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300 K shows that Coulomb interaction U in the range of 4.97–5.42 eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.

Anisotropic properties of TaS2

The anisotropic properties of 1T- and 2H-TaS2 are investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exhibit anisotropic properties and the calculated electronic specific-heat coefficient γ of 2H-TaS2 accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the exx(ω) spectra corresponding to the electric field E perpendicular to the z axis show excellent agreement with the measured results except for the e1xx(ω) of 1T-TaS2 below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio P of 1T and 2H phases it is found that the anisotropy in 2H-TaS2 is stronger than that in 1T-TaS2.

Structural Evolution of Nanostructured γ-Ni-28Fe Alloy Investigated by Using the Internal Friction Technique

The structural evolution of nanostructured ?-Ni-28Fe alloy (n-Ni-Fe) (grain size d~30?nm), synthesized by the mechno-chemical method, was investigated by using the internal friction technique combined with differential scanning calorimetry (DSC) in the temperature range from 300?K to 670?K. An internal friction peak with typical characteristics of the first-order phase transition was observed in the vicinity of 620?K, which corresponds to a broad exothermic process revealed by using DSC. These results can be explained as the structural changes from the disordering to the ordering transition in the n-Ni-Fe sample.

Chemical reaction of in-situ processing of NiAl/Al2O3 composite by using thermite reaction

NiAl/Al2O3 composite were synthesized by thermite reaction of nickel oxide and aluminum powder mixtures. The phase, the microstructure of the composite, as well as the thermite reaction mechanism, were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) combined with differential scanning calorimetry (DSC). The experimental results show that the thermite reaction leads to the interpenetrating network structure of NiAl/Al2O3 at 1223K for 60 min and the chemical reaction apparent activation energy is Eap=166.960±13.496 kJ·mol−1 in the NiO/Al system.

Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics

(Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ~ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ~ 0.24 is achieved at ~ 1000 K for the samples sintered at 1648 K and 1748 K, which was ~ 71% larger than that (0.14 at ~ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.