[Show abstract][Hide abstract] ABSTRACT: The Li-doped Ni–Si–O thin films ( Li <sub>x</sub> Ni <sub>0.90-x</sub> Si <sub>0.10</sub> O , x=0.0–0.05 ) have been prepared by a sol-gel spin-coating method on silicon and quartz glass substrates. Analysis of phase composition and microstructure indicates that the films consist of cubic NiO phase and amorphous phase as annealed at 700 ° C for 5 min . With the Li-doping concentration increasing, the core-level photoemission spectra show that a loss of the double-peak structure of the Ni 2p<sub>3/2</sub> main line can be observed and current density of the films increases greatly, which should be ascribed to the increase of the hole carriers induced by the Li doping. Ultraviolet-visible absorption spectra indicate that the absorption edge of the films exhibits a redshift due to the related defects.
No preview · Article · Sep 2006 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: M2MgSi2O7:Eu, Dy (M: Ca, Sr, Ba) phosphors were prepared via sintering at 1300 °C for 3 h in a weak reductive atmosphere of flowing 5% H2–95% N2 gas. The emission spectra of these phosphors showed that the main emissions are peaking at 537.5, 475.6 and 500.3 nm due to 4f → 5d transitions of Eu2+. The decay curves indicated that all of these phosphors have long afterglow feature, especially Sr2MgSi2O7:Eu, Dy phosphor. It is the Dy3+ trap levels that resulted in the long afterglow in M2MgSi2O7 hosts.
No preview · Article · Dec 2003 · Materials Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Eu3+-activated Y2O3 phosphor co-doped with Ti4+ or/and Mg2+ ions were prepared by calcinating the precursor powders in the 98%N2–2%H2 atmosphere. Red long afterglow was observed in the Y2O3:Eu3+, Ti4+, Mg2+ after excitation by 254 nm light, and the duration can reach nearly 1.5 h in the light perception of the dark-adapted human eyes (0.32 mcd/m2). The main emission peaks were ascribed to Eu3+ ions transition from 5DJ (J=0,1,2) to 7FJ (J=0,1,2,3,4), and the afterglow may be ascribed to some suitable complex trap centers produced by the introduction of Ti4+ and Mg2+ ions in the Y2O3 host lattice.
No preview · Article · Oct 2003 · Journal of Alloys and Compounds
[Show abstract][Hide abstract] ABSTRACT: Bulk samples of quasi-binary compounds in the Sn(Pb)Te-Bi2Te3 system were prepared by solvothermal method followed by a sintering procedure of compacted pellets. The formation mechanism
of the precursor powders, microstructure and thermoelectric properties of the final bulk samples were studied.
No preview · Article · Oct 2003 · Science in China Series E Technological Sciences
[Show abstract][Hide abstract] ABSTRACT: (Na0.5Bi0.5)(1−1.5x)EuxTiO3 ceramics have been prepared by solid state reaction at 1120°C for 2 h. Scanning electronic micrograph results indicate that the doped Eu2O3 can prohibit the grain growth. With increasing the doped amount of Eu2O3, the phase transformation (rhombohedral→cubic) can be observed in the X-ray diffraction patterns, and correlated with a strong decrease in the piezoelectric properties d33. The dielectric constants of poled and unpoled Na0.5Bi0.5TiO3 (NBT)-0 samples vary greatly as compared to NBT-5 sample due to the change of crystal structure.
No preview · Article · May 2003 · Materials Science and Engineering B
[Show abstract][Hide abstract] ABSTRACT: Oxide ceramics have recently attracted much attention as candidate
thermoelectric materials due to their special potential for applications
in power generation using waste heat. In this paper, (Na<sub>x</sub>Ca
(x=0.05-0.2) polycrystalline samples with a layered structure were
prepared by a sol-gel method followed by a low-temperature sintering
procedure. The electrical conductivity, the power factor and thermal
conductivity basically increase with increasing temperature. The figure
of merit is smaller than that of traditional thermoelectric alloys,
which is about 1.1×10<sup>-4</sup> K<sup>-1</sup> at 700°C in
the sample (Na<sub>x</sub>Ca<sub>1-x</sub>)<sub>3</sub>Co<sub>4</sub>O
[Show abstract][Hide abstract] ABSTRACT: Bismuth telluride based alloys have been a class of important thermoelectric materials. In this paper, polycrystalline samples of ternary compounds in the SnTn-Bi<sub>2</sub>Te<sub>3</sub> system were prepared by a rapid quenching of the melt followed by a sintering procedure of compacted pellets. The microstructure and thermoelectric properties, including Seebeck coefficient, electrical and thermal conductivities, of the samples were measured. The influence of processing routes, and constituent concentration on the thermoelectric properties was studied and discussed
[Show abstract][Hide abstract] ABSTRACT: Performance of thermoelectric materials and devices depends upon
various features on different levels from microscopic to macroscopic
scales. On the atomic scale, to find new multi-component compounds with
complex electronic and crystal structures is a way to high-Z
thermoelectric materials. On the nano-scale, quantum wells, wires and
dots are considered to be the dawn for breaking the traditional barrier
of ZT~1 existing for several decades. From the point of view of
microstructure, inhomogeneities in thermoelectric materials, such as
interfaces/grain-boundaries and inclusions, have significant influences
on their thermoelectric properties. On the macroscopic scale, the
thermoelectric device functions depend on thermoelectric materials used
for building the device and device configuration (such as multistage or
segmented devices). This review briefly presents the state-of-the-art
and perspectives in the multiscale understanding of thermoelectric
materials and devices