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Now showing items 65 - 80 of 89

  • The effects of stacking patterns and interlayer coupling on electronic and optical properties of bilayer BiI3

    Shen, Chenhai   Wang, Guangtao  

    Based on the density functional theory, we investigate the effects of stacking patterns and interlayer coupling on the stability, electronic structure and optical properties of bilayer (BL) BiI3 by utilizing first-principles methods. The stability and electronic structure are significantly influenced by the stacking patterns and interlayer distances. Moreover, the results show that the most stable pattern has the smallest equilibrium interlayer distance among all eight considered stacking cases. Although the nature of band gap of each stacking pattern is indirect band gap, interestingly, for seven considered patterns, the transition from indirect to direct occurs when the interlayer distance is below the equilibrium distance. The optical properties of BL BiI3 are sensitive to interlayer distances.
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  • Intrinsically Low Thermal Conductivity in BiSbSe3:A Promising Thermoelectric Material with Multiple Conduction Bands

    Liu, Xiaoying   Wang, Dongyang   Wu, Haijun   Wang, Jinfeng   Zhang, Yang   Wang, Guangtao   Pennycook, Stephen J.   Zhao, Li-Dong  

    Bi2Se3, as a Te-free alternative of room-temperature state-of-the-art thermoelectric (TE) Bi2Te3, has attracted little attention due to its poor electrical transport properties and high thermal conductivity. Interestingly, BiSbSe3, a product of alloying 50% Sb on Bi sites, shows outstanding electron and phonon transports. BiSbSe3 possesses orthorhombic structure and exhibits multiple conduction bands, which can be activated when the carrier density is increased as high as approximate to 3.7 x 10(20) cm(-3) through heavily Br doping, resulting in simultaneously enhancing the electrical conductivities and Seebeck coefficients. Meanwhile, an extremely low thermal conductivity (approximate to 0.6-0.4 W m(-1) K-1 at 300-800 K) is found in BiSbSe3. Both first-principles calculations and elastic properties measurements show the strong anharmonicity and support the ultra-low thermal conductivity of BiSbSe3. Finally, a maximum dimensionless figure of merit ZT similar to 1.4 at 800 K is achieved in BiSb(Se0.94Br0.06)(3), which is comparable to the most n-type Te-free TE materials. The present results indicate that BiSbSe3 is a new and a robust candidate for TE power generation in medium-temperature range.
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  • Realizing High-Ranged Out-of-Plane ZTs in N-Type SnSe Crystals through Promoting Continuous Phase Transition

    Chang, Cheng   Wang, Dongyang   He, Dongsheng   He, Wenke   Zhu, Fangyuan   Wang, Guangtao   He, Jiaqing   Zhao, Li-Dong  

    Thermoelectric technology enables direct conversion between heat and electricity. The conversion efficiency of a thermoelectric device is determined by the average dimensionless figure of merit ZT(ave). Here, a record high ZT(ave) of approximate to 1.34 in the range of 300-723 K in n-type SnSe based crystals is reported. The remarkable thermoelectric performance derives from the high power factor and the reduced thermal conductivity in the whole temperature range. The high power factor is realized by promoting the continuous phase transition in SnSe crystals through alloying PbSe, which results in a higher symmetry of the crystal structure and the correspondingly modified electronic band structure. Moreover, PbSe alloying induces mass and strain fluctuations, which enables the suppression of thermal transport. These findings provide a new strategy to enhance the thermoelectric performance for the continuous phase transition materials.
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  • Electronic structures and magnetism of YM2Ge2 (M=Mn–Cu): Ge-hight dependent magnetic ordering in YFe2Ge2

    Wang, Guangtao   Shi, Xianbiao  

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  • Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n-Type PbS

    Xiao, Yu   Wang, Dongyang   Zhang, Yang   Chen, Congrun   Zhang, Shuxuan   Wang, Kedong   Wang, Guangtao   Pennycook, Stephen J.   Snyder, G. Jeffrey   Wu, Haijun   Zhao, Li-Dong  

    Low-cost and earth-abundant PbS-based thermoelectrics are expected to be an alternative for PbTe, and have attracted extensive attentions from thermoelectric community. Herein, a maximum ZT (ZT(max)) approximate to 1.3 at 923 K in n-type PbS is obtained through synergistically optimizing quality factor with Sn alloying and PbTe phase incorporation. It is found that Sn alloying in PbS can sharpen the conduction band shape to balance the contradictory interrelationship between carrier mobility and effective mass, accordingly, a peak power factor of similar to 19.8 mu Wcm(-1)K(-2) is achieved. Besides band sharpening, Sn alloying can also narrow the band gap of PbS so as to make the conduction band position between Pb0.94Sn0.06S and PbTe well aligned, which can benefit high carrier mobility. Therefore, incorporating the PbTe phase into the Pb0.94Sn0.06S matrix can not only favorably maintain the carrier mobility at similar to 150 cm(2)V(-1)s(-1) but also suppress the lattice thermal conductivity to similar to 0.61 Wm(-1)K(-1) in Pb0.94Sn0.06S-8%PbTe, which contributes to a largely enhanced quality factor. Consequently, an average ZT (ZT(ave)) approximate to 0.72 in 300-923 K is achieved in Pb(0.94)Sn(0.0)6S-8%PbTe that outperforms other n-type PbS-based thermoelectric materials.
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  • FER1L4/miR-372/E2F1 works as a ceRNA system to regulate the proliferation and cell cycle of glioma cells

    Xia, Liang   Nie, Dekang   Wang, Guangtao   Sun, Caixing   Chen, Gao  

    Long non-coding RNAs have recently become a key regulatory factor for cancers, whereas FER1L4, a newly discovered long non-coding RNA, has been mostly studied in gastric carcinoma and colon cancer cases. The functions and molecular mechanism of FER1L4 have been rarely reported in glioma malignant phenotypes. In this study, it was found that the expression of LncRNA FER1L4 is upregulated in high-grade gliomas than in low-grade cases and that a high expression of LncRNA FER1L4 predicts poor prognosis of gliomas. Meanwhile, in vitro study suggests that expression of FER1L4 with SiRNA knockdown obviously suppresses cell cycle and proliferation. It is further demonstrated by experiments that the FER1L4 knockdown suppresses growth of in vivo glioma. Besides, it is found in our study that LncRNA FER1L4 expression is positively correlated with E2F1 mRNA expression. After knockdown of FER1L4 expression, E2F1 expression is significantly down-regulated, whereas the expression of miR-372 is significantly up-regulated; the up-regulation of miR-372 leads to significant down-regulation of FER1L4 and E2F1 expression. In addition, it is also found that FER1L4 can be used as competitive endogenous RNA to interact or bind with miR-371 and thereby up-regulate E2F1, thus promoting the cycle and proliferation of glioma cells. It may be one of the molecular mechanisms in which FER1L4 plays its oncogene-like role in gliomas.
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  • FER1L4/miR‐372/E2F1 works as a ceRNA system to regulate the proliferation and cell cycle of glioma cells

    Xia, Liang   Nie, Dekang   Wang, Guangtao   Sun, Caixing   Chen, Gao  

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  • Electronic structure and thermoelectric properties of Pb-based half-Heusler compounds: ABPb (A?=?Hf, Zr; B?=?Ni, Pd)

    Wang, Guangtao   Wang, Dongyang  

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  • Electronic structure,optical and thermoelectric properties of half-Heusler ZrIrX(X =3D As,Sb,Bi):a first principles study

    Wei, Junhong   Wang, Guangtao  

    The electronic structure, optical and thermoelectric properties of half-Heusler ZrIrX (X=3D As, Sb, Bi) compounds were investigated under pressure by using the modified Becke and Johnson exchange potential. The band gaps of ZrIrAs and ZrIrBi increase from tensile strain (epsilon =3D 5%) to compressive strain (epsilon =3D -5%), and at about e =3D -4% they changed from indirect to direct band gaps. Their absorption efficiencies increase from compressive to tensile strain in the low energy (<=3D 2.8 eV). For p-type doped compounds, the Seebeck coefficients and the power factors increase from tensile to compressive strain. While the the Seebeck coefficients and the power factors of n-type compounds, first increase and then decrease from tensile to compressive strain, reaching the largest values at the critical strain (direct-indirect transition). ZrIrSb is an indirect band gap insulator, but it translates to direct band gap insulator when the tensile strain epsilon >=3D 2%.
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  • Electronic structure and thermoelectric properties of Pb-based half-Heusler compounds:ABPb (A =3D Hf,Zr; B =3D Ni,Pd)

    Wang, Guangtao   Wang, Dongyang  

    The electronic structure and thermoelectric properties of half-Heusler ABPb (A =3D Hf, Zr; B =3D Ni, Pd) compounds were investigated by the first-principles calculation. Our results indicate all the four compounds are narrow-gap semiconductors. The value of power factor over relaxation time (S-2 sigma/tau) first increases and then decreases with carrier concentration increasing, because of the narrower band gap. The optimal p-or n-type doping concentrations with different temperature have been estimated. Comparing with the experimental data of ZrNiPb, we get the thermopower S, power factor S-2 sigma and the maximum power factor as a function of carrier concentration and temperature. Our calculated power factors are in good agreement with the experimental data, and give some suggestions to improve the thermoelectric properties. (C) 2016 Elsevier B.V. All rights reserved.
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  • Fabrication of hydroxyapatite/hydrophilic graphene composites and their modulation to cell behavior toward bone reconstruction engineering

    Wang, Pengjun   Yu, Tengbo   Lv, Qiulan   Li, Shaoke   Ma, Xuexiao   Yang, Guanpin   Xu, Daxing   Liu, Xiu   Wang, Guangtao   Chen, Zeqing   Xing, Shi-chao  

    Cell adhesion was the first step of bone reconstruction. While hydroxyapatite (HA)/graphene composites had been utilized for improving the cell adhesion and bone osteogenesis, the impact of cell adhesion and HA/graphene composites, especially HA/hydrophilic graphene (HG) composites, on internal interaction force and external surface properties remained poorly understood. Here, higher stability HA/HG composites were synthesized without extra ion introduction with in situ self-assembling method. And with XRD, FT-IR, XPS and Raman analyses, the evidences of the formation of HA and the introduction of HG was clear. TEM and SEM images showed the net-like spatial structure due to the internal interaction force between HA and HG, which provided the strain stimulation for cell adhesion. Subsequently, the external surface properties of HA/HG composites demonstrated that the roughness and hydrophilic ability of HA/HG composites could be artificially regulated by increasing the content of HG. Besides, the cell proliferation rate of HA/HG composites had been investigated. Compared to the intrinsic HA, HA/5%HG possessed the higher cell proliferation rate (264.81%) and promoted the spreading and growth of MC3T3-E1 cells. Finally, the regulation mechanism between HA/HG and cell adhesion were illuminated in detail. The excellent regular behavior of HA/HG composites for cell adhesion made them promising candidates for bone reconstruction and repairing. The present work provided the reference for the design of modifiable biomaterials and offered much inspiration for the future research of bone reconstruction engineering.
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  • Electronic structure and optical properties of Cs2AX2′X4 (A=Ge,Sn,Pb; X\r \r ,X=Cl,Br,I)

    Wang, Guangtao   Wang, Dongyang   Shi, Xianbiao  

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  • Gutzwiller Density Functional Studies of FeAs-Based Superconductors: Structure Optimization and Evidence for a Three-Dimensional Fermi Surface

    Wang, GuangTao   Qian, Yumin   Xu, Gang   Dai, Xi   Fang, Zhong  

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  • First-principles study of the electronic structure and thermoelectric properties of LaOBiCh\r 2\r (Ch=S, Se)

    Wang, Guangtao   Wang, Dongyang   Shi, Xianbiao   Peng, Yufeng  

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  • Remarkable electron and phonon band structures lead to a high thermoelectric performance ZT > 1 in earth-abundant and eco-friendly SnS crystals

    He, Wenke   Wang, Dongyang   Dong, Jin-Feng   Qiu, Yang   Fu, Liangwei   Feng, Yue   Hao, Yujie   Wang, Guangtao   Wang, Jinfeng   Liu, Chang   Li, Jing-Feng   He, Jiaqing   Zhao, Li-Dong  

    Tin selenide (SnSe), a simple binary compound with low-cost, earth-abundant and eco-friendly elements, has aroused extensive interest in the thermoelectric community on account of its promising power generation. Herein, we report a much more advantageous SnS crystal with promising thermoelectric performance, as an alternative to SnSe. We found that the maximum ZT > 1.0 at 873 K and high device ZT (ZT(dev)) > 0.57 from 300 to 873 K can be achieved in hole-doped SnS crystals, projecting a conversion efficiency of approximate to 10.4%. We attribute the excellent performance of SnS to its remarkable electron and phonon band structures. SnS possesses multiple valence bands, which can be activated by hole doping through pushing the Fermi level deep into the valence band structure, and activating several Fermi pockets to produce enhanced Seebeck coefficients and high power factors approximate to 30 W cm(-1) K-2 at 300 K. Meanwhile, the anharmonic and anisotropic bonding of SnS leads to a low thermal conductivity, which ranges from 0.65 to 0.85 W m(-1) K-1 at 873 K. Our results indicate that SnS is a promising thermoelectric material for energy conversion applications in low and moderate temperature ranges.
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  • Intrinsically Low Thermal Conductivity in BiSbSe 3 : A Promising Thermoelectric Material with Multiple Conduction Bands

    Liu, Xiaoying   Wang, Dongyang   Wu, Haijun   Wang, Jinfeng   Zhang, Yang   Wang, Guangtao   Pennycook, Stephen J.   Zhao, Li-Dong  

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