分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-08
摘要: The thermoelectric properties of two-dimensional graphyne sheets are investigated by using first- principles calculations and the Boltzmann transport equation method. The electronic structure indicates a semiconducting phase for graphyne, compared with the metallic phase of graphene. Consequently, the obtained Seebeck coefficient and the power factor of graphyne are much higher than those of graphene. The calculated phonon mean free path for graphene is 866 nm, which is in good agreement with the experimental value of 775 nm. Meanwhile the phonon mean free path of graphyne is only 60 nm, leading to two order lower thermal conductivity than graphene. We show that the low thermal conductivity of graphyne is due to its mixed sp/sp2 bonding. Our calculations show that the optimized ZT values of graphyne sheets can reach 5.3 at intermediate temperature by appropriate doping.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Gadolinium gallium aluminum garnet (GGAG) is a very promising host for the highly efficient luminescence of Ce3+ and shows potential in radiation detection applications. However, the thermodynamically metastable structure would be slanted against it from getting high transparency. To stabilize the crystal structure of GGAG, Yb3+ ions were codoped at the Gd3+ site. It is found that the decomposition of garnet was suppressed and the transparency of GGAG ceramic was evidently improved. Moreover, the photo- luminescence of GGAG:Ce3+,xYb3+ with different Yb3+ contents has been investigated. When the Ce3+ ions were excited under 475 nm, a typical near-infrared region emission of Yb3+ ions can be observed, where silicon solar cells have the strongest absorption. Basing on the lifetimes of Ce3+ ions in the GGAG:Ce3+,xYb3+ sample, the transfer efficiency from Ce3+ to Yb3+ and the theoretical internal quantum efficiency can be calculated and reach up to 86% and 186%, respectively. This would make GGAG:Ce3+,Yb3+ a potential attractive downconversion candidate for improving the energy conversion efficiency of crystalline silicon (c-Si) solar cells.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: We study type I clathrate Ba8Cu5.1Ge40.2Sn0.7 single crystals (space group Pm3"n, no. 223, a 1⁄4 10.7151(3)) grown using a Sn flux method. Microprobe analysis and single-crystal X-ray diffraction reveal a small amount of Sn embedded in the Cu/Ge framework, which increases disorder at the guest Ba sites. Ba8Cu5.1Ge40.2Sn0.7 is diamagnetic with a susceptibility of $2.8 10 7 emu g 1 and shows metal-like behavior (dr/dT > 0) with a low charge carrier concentration of 0.5 e per unit cell at 300 K. The single crystals show a relatively high carrier mobility (m (300 K) 1⁄4 11.9 cm2 V 1) and very low lattice thermal conductivity ($0.6 W m 1 K 1). The thermoelectric figure of merit ZT of Ba8Cu5.1Ge40.2Sn0.7 single crystals reaches a maximum value of 0.6 at 773 K, which can be further improved by adjusting the chemical composition.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Tin telluride (SnTe) has recently attracted much attention as a promising thermoelectric material. In this work, SnTe is alloyed with additional Pb, and the high density crystalline ingots of SnPbxTe (x 1⁄4 0, 0.02, 0.04, and 0.06) have been synthesized by a zone-melting method. Through this method, SnPbxTe samples show larger power factors than those prepared by other methods, and a maximum value of 30.5 mW cm 1 K 2 at 823 K has been reached in p-type SnPb0.02Te, which is the highest value reported so far. As a result, a promising figure of merit ZT of $0.81 has been obtained at 823 K.
提交时间: 2017-05-02
摘要: principles calculations. The obtained phonon frequencies agree well with the measurements of Raman scattering. The thermodynamic properties are calculated within quasi-harmonic approximation, and the measured lattice thermal conductivity is well reproduce
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A novel layered GGAG/YAG composite scintillation ceramic can be prepared at 1650◦C using an easily accessible preparation procedure. The oxygen sintering-hot isostatic pressing method implemented in this work can significantly shorten the preparation period of scintillation ceramics. The ceramic exhibits regular grain microstructure. Interface of the composite ceramic is clean and straight. As prepared, the layered Ce:GGAG/Cr:YAG composite ceramic can emit a broad range of photons with wavelength from 500 to 750 nm under excitation. The integral spectra is composed of three parts: emitted photons of Cr:YAG and Ce:GGAG and emitted light of Cr:YAG excitated by the photons emitted by the Ce:GGAG ceramic layerprepared by the proposed method. The method accomplished in this work can significantly improve the exploration of full spectrum scintillation/luminescence ceramics preparation and spectra designation.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A micron size YAG:Ce/YAG:Cr core–shell structure was designed and accomplished via the urea homogeneous precipitation method using the YAG:Ce spherical core as the introduced second phase. A well dispersed gel like encapsulation structure can be achieved before the formation of YAG:Ce/YAG:Cr core–shell particles via a calcination process. As prepared YAG:Ce/YAG:Cr particles can emit a broad range of photons from 500 to 750 nm with excitation light of 433 nm. A schematic illustration showing the mechanism of excitation–emission of the core–shell particles is presented. The integral spectra are composed of three parts: emission photons of YAG:Cr, YAG:Ce, and emission light of YAG:Cr excited by the emission photons of the YAG:Ce core according to the proposed mechanism. The method accomplished in this work can significantly improve the exploration of full spectrum luminescent powder synthesis and spectra designation.
提交时间: 2017-05-02
摘要: Urea precipitation method has been developed as an important approach for the preparation of inorganic particles with defined morphology and composition. In present work, we provide survey of the technological developments and achievements mainly on the a
提交时间: 2017-05-02
摘要: Rechargeable aqueous metal-ion batteries made from non-flammable and low-cost materials offer promising opportunities in large-scale utility grid applications, yet low voltage and energy output, as well as limited cycle life remain critical drawbacks in t
提交时间: 2017-05-02
摘要: In order to obtain a uniform transparent ceramic scintillator, well-dispersed fine starting powders with high-purity, small grain size, spherical morphology and high sinter-ability are necessary. In this study, Ce3+ doped gadolinium aluminum gallium garne