15% Ag-added cubic perovskites Sr0.9La0.1TiO3 and Ruddlesden-Popper(RP) phases Sr2.7La0.3Ti2O7 were fabricated via hydrothermal synthesis,cold pressing and high-temperature sintering.The structure and thermoelectric properties were also investigated for all samples.The results indicated that Ag precipitated as a second phase.Ag addition made electrical conductivity and absolute Seebeck coefficient enhanced,as a result,the ZT values were enhanced both for two series.Compared with cubic perovskite,RP phase was subjected to smaller impact by Ag addition.The reasons for enhancing ZT value and the different impact for two series by Ag addition were also discussed.
The CoFe_2alloy(CF) was prepared by reducing CoFe_2O_4 in the H_2 ambient. Subsequently the CF sample was nitrided in the NH_3 atmosphere to produce the composite of CoFe_2N and CoFe_2. The magnetostriction, thermal expansion, resistivity and corrosion resistance of CF sample and the nitrided sample(CFN)at 1000?C were investigated. The saturation magnetostriction coefficiency λ_s and thermal expansion coefficient ? at 300 K for the nitrided CFN were 50 ppm and 10 ppm/K, respectively, approximately equal to those for the CF sample. However, compared with CF, CFN presents a decrease in temperature coefficient R_λ(300 K) of magnetostriction by 11%. The smaller resistivity and improved corrosion resistance in the H_2SO_4 solution may expand the applications of the CoFe_2 in the fields needing lower resistivity or in the acidic environment.
Photoluminescence properties of Sr 2.5 Dy 1/3-x Eu x V 2 O 8(x=0,0.06,0.12,0.18,0.24,0.33) were investigated.The excitation spectra included a broad band in the short wavelength region and several sharp lines in the longer wavelength region,and the spectral origin were discussed.The emission spectra were measured in two different exciting ways,i.e.,exciting the VO 4 group at 270 nm and the Eu 3+ ion at 398 nm,respectively,and the energy transferring process was reasonably suggested.Furthermore,multi-color emission could be achieved in Sr 2.5 Dy 1/3-x Eu x V 2 O 8,indicating that the studied samples had potential applications in the white light emitting diodes.Further investigation showed that reducing the concentration of Eu 3+ and Dy 3+ and introducing Bi 3+ as a sensitizer ion greatly enhanced the emission intensity.
Taking the Mn4O4 cluster as a model system,the spin-polarized transport properties of the small cluster system were systematically probed. The theoretical investigations are based on density-functional theory and nonequilibrium Green's functional method. The equilibrium transport mechanism is illustrated by the band structure of the electrode, the electronic structure of the Mn4O4 cluster and the coupling between the cluster and the electrodes. To well understand the non-equilibrium mechanisms, one straightforward and simple band-matching model was proposed. Moreover, such a band-matching model can be extended to well illustrate the transport properties of other nano-scale systems.
