热电材料PbTe1-xSex的高压制备及电学性能研究

 利用高温高压技术,制备了热电材料PbTe和PbSe的固溶体合金PbTe_1-xSe_x,在室温下对其结构及电学性质进行了研究。X射线衍射（XRD）测试结果表明：PbTe_1-xSe_x具有NaCl结构;晶格常数随着Se含量（x）的增加而减小;PbTe_1-xSe_x的电阻率和Seebeck系数的绝对值随x的增大而减小;功率因子随x的增大先增大而后减小,当x=0.1时功率因子最高,达到21.7 μW/(cm·K²),比相同条件下制备的PbTe高20%。     

高压下Sr2FeMoxNb1-xO6 (x=0, 0.3)的电学性质和结构稳定性

 采用金刚石压砧高压装置，研究了双钙态矿结构化合物Sr₂FeNbO₆及其掺杂物Sr₂FeMo_0.3Nb_0.7O₆在室温下，20 GPa内电阻和电容随压力的变化，并发现Sr₂FeNbO₆在7.5 GPa左右压力下发生了相变，而Sr₂FeMo_0.3Nb_0.7O₆的相变发生在2.8 GPa左右。并结合这两个样品的高压下的同步辐射能散X射线衍射实验，进一步证明了这两种相变是电子结构相变引起的。     

高压制备Ag_(1-x)Pb_(18)SbTe_(20)及其电学性能的研究

采用高压方法制备了Ag偏离化学计量比的Ag1-xPb18SbTe20(x=0,0.3,0.6)样品,研究了Ag含量及温度对样品电学输运性能的影响。X射线衍射测试结果表明,样品具有单相NaCl结构,晶格常数随Ag含量的减少而变小。电学输运性能测试表明:与常规制备方法相比,高压方法制备的AgPb18SbTe20样品的电导率较高;样品电导率随x的增大而逐渐增大,x=0.6时,室温条件下的样品电导率高达1 598.4S/cm。随着温度的升高,Seebeck系数增大,电导率减小。300℃时,Ag0.4Pb18SbTe20样品的功率因子达到最大值,约为1.97mW/(m·K2)。     

Structural Phase Transition and a Mutation of Electron Mobility in Zn_xCd_(1-x)O Alloys

We investigate the electronic structures and phase stability of ZnO, CdO and the related alloys in rocksalt(B1)and wurzite(B4) crystal, using the first-principle density functional theory within the hybrid functional approximation. By varying the concentration of Zn components from 0% to 100%, we find that the Zn_xCd(1-x)O alloy undergoes a phase transition from octahedron to tetrahedron at x = 0.32, in agreement with the recent experimental findings. The phase transition leads to a mutation of the electron mobility originated from the changes of the effective mass. Our results qualify Zn O/Cd O alloy as an attractive candidate for photo-electrochemical and solar cell power applications.     

巨磁阻材料Sr2CrWO6高压下的结构稳定性和电学特性

 采用金刚石压砧高压装置，研究了双钙钛矿结构化合物Sr₂CrWO₆在室温下、34.5 GPa压力内的同步辐射X射线衍射谱，发现在9.6 GPa的压力点样品的结构有所变化。结合室温下20 GPa内电阻和电容随压力的变化，证明样品在9 GPa附近发生了晶体结构相变，而在2~5 GPa的压力范围内样品发生了电子结构相变。     

高压下纳米尺寸Sr2FeMoO6粉末的结构稳定性和电学特性的研究

 采用高分子网络凝胶法，通过控制其化学反应过程，合成了高纯的多晶纳米级粉末Sr₂FeMoO₆样品A（50 nm）和样品B（100 nm）。对其在高压下的结构稳定性和电学性质进行了研究，并将样品A和样品B的实验结果与已报道的粒度达微米级的块状Sr₂FeMoO₆样品C的实验结果进行了对比。在实验测量范围内，样品A（50 nm）呈现出最大的体弹模量B₀，并在电阻-压力曲线中，电阻下降区域表现出相对较缓的变化率，晶界效应可以用来很好地解释此结果。电学性质测量实验表明，样品在高压下发生了电子结构相变。     

Structural and Thermodynamic Properties of TiAl intermetallics under High Pressure

The structural and thermodynamic properties of TiAl intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method.It is found that the ratio of lattice parameter c to a keeps almost constant with a value of 1.02 under the pressure from 0 to 20 GPa,which agrees well with the experimental results.With the pressure increasing from 20 to 45 GPa the values of c/a decrease almost linearly from 1.02 to 0.99.These calculated results indicate under low pressure the variation rate for a-axis is almost the same to that for c-axis,but under higher pressure the variation for a-axis is smaller than along c-axis.Through the quasi-harmonic Debye model,the equation of state(EOS) of TiAl intermetallics,as well as the thermal expansion and heat capacity at various pressures and temperatures are also studied.     

CdxZn1-xO：Eu^3＋荧光粉的制备及其发光性质

采用高温固相法在1100℃下合成了Eu3 掺杂的CdxZn1-xO发光材料。采用X射线衍射对所合成样品的结构进行了表征。分析了不同浓度Cd2 的掺杂对于样品发光及激发峰位置的影响。通过对荧光光谱的测试,表明Cd2 的引入使得体系的禁带宽度变窄,并且通过Cd2 掺杂浓度的变化,可以对样品的激发光谱峰值在380～410nm进行调制,样品的发光以520nm处的宽带发射为主,并没有明显的Eu3 的特征发射,表明基质与Eu3 之间的能量传递并不有效。在加入Li 作为电荷补偿剂之后,出现了来自Eu3 的特征发射,相应的发射光谱的发射主峰位于609nm。样品380～410nm的激发峰范围覆盖了紫外LED芯片的输出波长。因此,这种荧光粉是一种可能应用在白光LED上的红色荧光粉材料。     

高压下钡的硫化物的结构相变和光学性质研究(英文)

利用基于密度泛函的第一性原理,计算了高压下钡的硫化物(BaS、BaSe和BaTe)的结构相变和光学性质。计算结果表明,这些化合物的压致结构相变是从NaCl型结构转变为CsCl型结构;对于结构转变压力和金属化转变压力,BaS为8.57 GPa和45.4 GPa,BaSe为7.44 GPa和36.5 GPa,BaTe则分别为5.67 GPa和16.7 GPa。光学性质计算结果显示:随着压力的增加,静态介电常数ε0不断增加,介电常数虚部ε2的峰值向高能方向移动(蓝移)。     

Zn_（1－x）Mg_xS_ySe_（1－y）四元半导体合金的拉曼散射光谱研究

用分子束外延方法在ＧａＡｓ（１００）衬底上生长了Ｚｎ１－ｘＭｇｘＳｙＳｅ１－ｙ四元半导体合金薄膜．用Ｘ－射线衍射方法确定了外延层的结构和晶格常数．测量了这些样品在平行和垂直两种不同几何配置下的拉曼散射光谱并对其特性做了研究。从实验上观察到了四类不同的晶格振动模：类ＺｎＳｅ的ＴＯ和ＬＯ模以及类ＺｎＳ和类ＭｇＳ的ＬＯ模，实验发现：在ＺｎＳｅ和ＺｎＳＳｅ中加入Ｍｇ使得类ＺｎＳｅ的ＴＯ和ＬＯ模的振动频率下降；同时，也使类ＺｎＳ模的频率随Ｓ的增加率减小。     

Structural properties of Pb2MnW(1-x)Re(x)O6 double perovskites

Pb2MnW(1-x)Re(x)O6 samples have been synthesized and their structure determined by powder x-ray diffraction. These samples undergo a first order structural phase transition between 413 and 445 K depending on the composition. Above this temperature, the samples are cubic. Below the transition temperature, solid solutions are found for x ≤ 0.2 and x ≥ 0.5. The W-rich samples adopt an orthorhombic cell whereas the Re-rich compounds are monoclinic. In the intermediate region, 0.2 < x < 0.5, both phases coexist. X-ray absorption spectra did not reveal significant changes in the local structure for Pb, Mn or Re atoms across the structural phase transition. All the atoms exhibit distorted environments in the whole series. In the case of Pb and W(Re) atoms, the local distortion remains in the high temperature phase. Samples with x ≤ 0.2 also show a sharp discontinuity in the dielectric permittivity at the phase transition temperature indicating the presence of a concomitant electrical ordering in the bulk grains. Such an anomaly in the dielectric constant is not observed for the x ≥ 0.5 samples, compatible with the lack of dipole ordering for this composition range. The different electrical behaviours also explain the differences in the entropy content for the two types of transition.     

Structural Properties of Anthracene Under High Pressure

The aim of our studies is to investigate the nature of intermolecular interactions in crystals based on aromatic molecules. For this purpose we carry out angle dispersive (ADXD) as well as energy dispersive (EDXD) X-ray diffraction experiments under pressure in combination with Rietveld refinement. The other approach is density functional theory (DFT), where our calculations are based on the experimentally obtained lattice parameters. In the present work we focus on anthracene C 14 H 10 (monoclinic space group P2 1 /a) as a representative for the herringbone structure that is common for rigid rod-like molecules. We discuss its structural properties as a function of pressure and find very good agreement between experiment and theory.     

Zn1-xCdx S合金薄膜的结构和光学性质

采用低压金属有机化学气相沉积(LP-MOCVD)技术,在普通石英衬底上制备出不同Cd组分(0．02,0．44,0．59,0．83,0．91)的Zn1-xCdxS合金薄膜材料。X射线测量表明样品为单一取向的纤锌矿结构,并且随着x的增加衍射峰位基本成线性地从ZnS衍射峰向CdS衍射峰移动。此外,在PL谱中还可以看出随着样品中Cd含量的增加,发光峰从3．66eV红移到2．43eV。根据发光峰位与Zn1-xCdxS中x的变化关系,推导出它们之间的关系近似为Eg(Zn1-xCdxS)=3．61-1．56x 0．38x^2。还探讨了不同Cd组分薄膜材料的X射线衍射峰半峰全宽以及发光峰半峰全宽的变化。     

金红石结构TiO2结构和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法以及准谐德拜模型研究了金红石TiO₂的结构和热力学性质.常温常压下所计算的晶格常数、体弹模量及其对压强的一阶导数与实验值和其他理论计算结果相符的较好.另外,我们还计算了体弹模量、热膨胀系数、热容与温度和压强的关系.     

Band Alignment for Ambipolar-Doping of Sn_xZn_(1-x) Te Alloys

Using the first-principles band-structure method and a special quasirandom structure(SQS) approach,we have systematically calculated the alloy bowing coefficients and the nature band offsets of SnxZn1-x Te alloys.We show that the bowing coefficients and band gaps of these alloys are sensitively composition dependent.Due to wave functions full overlapping and delocalization of the Sn outermost p orbits and Zn s orbits,the coupling between these states is very strong,resulting in a significant downshift of conduction band edge with the increase of the Sn concentration x,While the valence band edge keeps almost unchanged compared with that of the binary ZnTe,thus improving the possibility for ambipolar-doping.     

金红石结构TiO2结构和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法以及准谐德拜模型研究了金红石TiO2的结构和热力学性质。常温常压下所计算的晶格常数、体弹模量及其对压强的一阶导数与实验值和其他理论计算结果相符的较好。另外,我们还计算了体弹模量、热膨胀系数、热容与温度和压强的关系。     

Structural and superconducting properties of LaFeAs_(1-x)Sb_xO_(1-y)F_y

We report the antimony(Sb) doping effect in a prototype system of iron-based superconductors LaFeAsO1-yFy(y=0,0.1,0.15).X-ray powder diffraction indicates that the lattice parameters increase with Sb content within the doping limit.Rietveld structural refinements show that,with the partial substitution of Sb for As,the thickness of the Fe2As2 layers increases significantly,whereas that of the La2O2 layers shrinks simultaneously.So a negative chemical pressure is indeed "applied" to the superconducting-active Fe2As2 layers,in contrast to the effect of positive chemical pressure by the phosphorus doping.Electrical resistance and magnetic susceptibility measurements indicate that,while the Sb doping hardly influences the SDW anomaly in LaFeAsO,it recovers SDW order for the optimally-doped sample of y=0.1.In the meantime,the superconducting transition temperature can be raised up to 30 K in LaFeAs1-xSbxO1-yFy with x=0.1 and y=0.15.The Sb doping effects are discussed in term of both J1-J2 model and Fermi Surface(FS) nesting scenario.     

高压下Al基合金的凝固组织特征

 研究了亚共晶或过共晶Al-Cu和Al-Si合金在5 GPa压力条件下凝固的显微组织特征。与常压相比,高压不仅会明显改变凝固组织形态,而且会使凝固组织尺寸发生变化,有时粗化,有时细化。凝固组织粗化还是细化与压力对液固两相区温度间隔的影响有关。当压力使液固两相区温度间隔增大时,凝固组织粗化,反之细化。此外,还提出了一种针对树枝晶和胞状晶两种不同形态组织的尺寸评价新方法。     

MgxZn1-xO粉体的制备及性能表征

MgxZn1-xO材料是一种新型的光电功能材料,近年来受到人们的广泛关注.文章采用Sol-Gel法制备了MgxZn1-xO粉体,研究Mg含量对MgxZn1-xO结构和发光性能的影响,结果表明在x从0到1的整个区间中MgxZn1-xO样品存在六方纤锌矿与面心立方两种结构,当x＜0.2时为六方纤锌矿结构,x＞0.8时为面心立方结构,在两者之间为其混合结构;光谱分析表明不同组分的MgxZn1-xO样品均具有紫外和可见发射特性,紫外发射峰位于370～384 nm,可见发射峰位于468 nm附近;粉体的平均粒径在100 nm左右.