Mg掺杂n型Sn基Ⅷ型单晶笼合物的结构及电传输特性

本文采用Sn自熔剂法,制备Mg掺杂Sn基单晶笼合物Ba₈Ga_16-XMg_XSn₃₀ （0 ≤ X ≤ 1.5）,并对其结构及电传输性能进行研究. 结果表明所制备化合物为具有空间群I43 m的Ⅷ型单晶笼合物,随Mg掺杂量的增加,对应化合物的熔点略有升高,晶格常数减小,掺杂样品中填充原子Ba的实际含量低于理想值8.0,其在十二面体空洞中的占有率约为0.93（Mg的名义含量X=1.5时）. 所有样品均表现为n型传导,Mg的掺入对材料的能带结构有一定影响,Mg掺杂后,样品的载流子浓度降低,Seebeck系数的绝对值、电阻率增加,Mg的名义含量X=1.5时,样品的功率因子在430 K附近取得最大值1.26×10^-3 W·m^-1·K^-2. 关键词： Ⅷ型笼合物 n型传导 单晶     

Ge掺杂n型Sn基VIII型单晶笼合物的制备及热电传输特性

采用Sn自熔剂法制备了具有n型传导的VIII型Ba8Ga16 xGexSn30(0 x 1.0)单晶笼合物,并对其结构和热电特性进行研究.研究结果表明:Ge在单晶中的实际含量较少,随着掺杂量的增加样品的晶格常数略有减小,Ge掺杂后样品的载流子浓度较掺杂前低,迁移率增加;所有样品的Seebeck系数均为负值,且绝对值较未掺杂样品低,但Ge掺杂后样品的电导率提高了62%;x=0.5的样品在500 K附近取得最大ZT值1.25.     

Ge掺杂n型Sn基Ⅷ型单晶笼合物的制备及热电传输特性

采用Sn自熔剂法制备了具有n型传导的Ⅷ型Ba₈Ga_16-xGe_xSn₃₀ （0 ≤ x ≤ 1.0）单晶笼合物,并对其结构和热电特性进行研究. 研究结果表明：Ge在单晶中的实际含量较少,随着掺杂量的增加样品的晶格常数略有减小,Ge掺杂后样品的载流子浓度较掺杂前低,迁移率增加;所有样品的Seebeck系数均为负值,且绝对值较未掺杂样品低,但Ge掺杂后样品的电导率提高了62%;x=0.5的样品在500 K附近取得最大ZT值1.25. 关键词： Ⅷ型笼合物 n型传导 热电性能     

Cd掺杂p型Ge基Ba8Ga16CdxGe30-x Ⅰ型笼合物的结构及热电特性

以Cd作为掺杂元素,用熔融法结合放电等离子体烧结(SPS)技术制备了具有不同Cd含量的Ba8Ga16CdxGe30-x(x=0.95,1.00,1.05,1.10) Ⅰ型笼合物,研究了Cd掺杂对其结构及热电性能的影响.Rietveld结构解析表明所制备的Ba8Ga16CdxGe30-x化合物为空间群pm3n的Ⅰ型笼合物,Cd原子主要占据在框架6c和16i位置上且具有较大的原子位移参数(ADP).所有样品均表现为p型传导,样品的载流子散射机制由低温的杂质电离散射为主逐渐过渡到高温的声学波散射为主.随Cd掺杂量的增加,对应化合物电导率逐渐增加,Seebeck系数逐渐降低.由于Cd原子较大的ADP,从而导致较低的晶格热导率,在室温附近,Ba8Ga16Cd1.10Ge28.90化合物的晶格热导率与Ba8Ga16Ge30化合物相比约降低38%.Ba8Ga16Cd1.00Ge29.00化合物的最大ZT值在600 K时为0.173.     

Zn掺杂n型笼合物Ba8Ga16-2xZnxGe30+x的热电传输特性

用高温熔融结合放电等离子烧结法制备了Zn掺杂单相n型Ba8Ga16-2xZnxGe30 x笼合物,探索了Zn对Ga的取代对其热电传输特性的影响规律.研究结果表明,n型Ba8Ga16-2xZnxGe30 x化合物的电导率随着x的增加逐渐增大,Seebeck系数随着x的增加而逐渐减小.当Zn完全取代Ga时,Ba8Zn8Ge38化合物的电导率反而急剧下降,Seebeck系数显著增大.Ba8Ga16-2xZnxGe30 x化合物的载流子迁移率随着温度的升高而降低,当Zn掺杂后,化合物的载流子迁移率有一定的增加,随着x的增加而逐渐增大.Ba8Ga16-2xZnxGe30 x化合物的热导率和晶格热导率变化规律类似,随着x的增加先减小后增大.在所有n型Ba8Ga16-2xZnxGe30 x笼合物中,Ba8Ga8Zn4Ge34化合物的ZT值最大,在1000 K时其最大ZT值达0.85.     

Zn掺杂P型Ba8Ga16ZnxGe30-x笼合物的合成及热电性能

用熔融法结合放电等离子烧结方法合成了Zn掺杂单相p型Ge基Ⅰ型笼合物Ba8Ga16ZnxGe30-x(x=3,4,5,6),探索Zn取代Ge对其热电性能的影响规律,结果表明:所制备的Ba8Ga16ZnxGe30-x化合物为p型传导,随Zn取代量x的增加,化合物室温载流子浓度Np逐渐增加,室温载流子迁移率μH和电导率逐渐降低.在所有试样中,Ba8Ga16Zn3Ge27化合物的Seebeck系数α在300—870K内始终最大,温度为300K时Seebeck系数为234μV/K,在700K附近达295μV/K.化合物的热导率随Zn取代量x的增加而降低.Ba8Ga16Zn3Ge27化合物在806K最大ZT值达0.38.     

熔体旋甩工艺对Zn掺杂Ⅰ-型Ba8Ga12Zn2Ge32笼合物微结构及热电性能的影响

采用新颖的熔体旋甩(MS)结合放电等离子烧结(SPS)技术制备了单相Zn掺杂的I-型Ba8Ga12Zn2Ge32笼合物,研究了熔体旋甩工艺对其微结构以及热电性能的影响.结果表明,MS得到的薄带自由面主要由300 nm-1 μm的小立方体单晶组成,薄带经SPS烧结后得到了具有大量层状精细结构的致密块体.与熔融+SPS工艺制备的试样相比,熔融+MS+SPS制备的Ba8Ga12Zn2Ge3笼合物室温载流子浓度增加而迁移率降低,在测试温度范围内,试样的电导率略有下降,Seebeck系数增加,热导率和晶格热导率显著降低,900 K时其晶格热导率从1.06 W/mK降低至0.42W/mK.熔融+MS+SPS制备的Ba8Ca12Zn2Ge32笼合物试样在900 K时其最大ZT值达到0.90,与熔融+SPS试样相比提高了75%.     

Cd掺杂p型Ge基Ba8Ga16CdxGe30-x Ⅰ型笼合物的结构及热电特性

以Cd作为掺杂元素,用熔融法结合放电等离子体烧结（SPS）技术制备了具有不同Cd含量的Ba₈Ga₁₆Cd_xGe_30-x（x=0.95, 1.00, 1.05, 1.10） Ⅰ型笼合物,研究了Cd掺杂对其结构及热电性能的影响.Rietveld结构解析表明所制备的Ba₈Ga₁₆Cd_xGe_{30- 关键词： p型笼合物 结构 热电性能}     

Zn掺杂p型Ba8Ga16ZnxGe30－x笼合物的合成及热电性能

用熔融法结合放电等离子烧结方法合成了Zn掺杂单相p型Ge基Ⅰ型笼合物Ba₈Ga₁₆Zn_xGe_30-x(x=3, 4, 5, 6)，探索Zn取代Ge对其热电性能的影响规律，结果表明：所制备的Ba₈Ga₁₆Zn_xGe_30-x化合物为p型传导，随Zn取代量x关键词： p型笼合物 合成 热电性能     

Zn掺杂n型笼合物Ba8Ga16-2xZnxGe30+x的热电传输特性

用高温熔融结合放电等离子烧结法制备了Zn掺杂单相n型Ba₈Ga_16-2xZn_xGe_30+x笼合物,探索了Zn对Ga的取代对其热电传输特性的影响规律.研究结果表明,n型Ba₈Ga_16-2xZn_xGe_30+x化合物的电导率随着x的增加逐渐增 关键词： 热电传输性能 n型笼合物 框架取代     

Weak effects in e±e± → e±e±

The prediction for the cross section of e^±e^± → e^±e^± is given, assuming one photon and W^o exchange. Pure W^o terms and transverse and longitudinal beam polarizations are included.     

Detailed W0 effects in e+e− → e+e−

The predicted cross section for the reaction e⁺e^?→e⁺e^? is presented assuming one photon and W⁰ exchange. Pure W⁰ terms and the W⁰ width are included.     

One-loop corrections to e+e− → e+e− in the weinberg model

Radiative corrections to Bhabha scattering are calculated in the simplest example of non-Abelian gauge theories. A detailed analysis of the higher-order effects is presented and the total differential cross section including weak corrections is evaluated at different angles in an energy range up to 70 GeV per beam. The effects of weak interactions appear to be negligible up to the production of the neutral vector boson.     

(e, 2e) spectroscopy

We present a detailed treatment of the theoretical and experimental aspects of the symmetric (e, 2e) reaction in atoms, molecules and solids. Two experimental arrangements are described for measuring angular correlations and separation energy spectra. the one arrangement employing coplanar and the other noncoplanar symmetric kinematics. The latter arrangement is shown to be particularly suitable for extracting structure information. The basic approximation, the factorized distorted-wave off-shell impulse approximation with fully distorted waves, is shown to correctly describe the reaction in some test cases, as does the phase distortion approximation. At energies of the order of 1200 eV the simple eikonal and plane wave approximations adequately describe the valence shell cross sections for light atoms and molecules containing first row elements. Energy independent structure information is obtained on: (a) shapes and magnitudes of the square of the momentum space wave functions for individual electron orbitals; (b) separation energies for individual ion eigenstates; (c) the characteristic orbital of each state; and (d) spectroscopic factors describing the probability that an eigenstate contains the principal configuration of a hole in the characteristic orbital for each eigenstate. Comparison is made with photoelectron spectroscopy and Compton scattering, since they separately yield some of the information obtained by the (e, 2e) method. A brief summary is given of other electron-electron coincidence experiments.     

QED to lowest order ine + e −→e + e −γγγ

We calculate the cross-section for the production ofe ⁺ e ^?γγγ ine ⁺ e ^? annihilation. The results are in agreement with the first observation of such a process by the ASP experiment at SLAC. The calculation also provides another example of the power of ‘spinor techniques’ in calculating Feynman amplitudes.     

Analyzing thee + e −→e + e − angular distibution at LEP

The analysis of the lepton angular distribution at LEP is reviewed and the specific concerns in the case ofe ⁺ e ^– final state are singled out. Studies of the physical information contained in thee ⁺ e ^– angular distribution are shown to justify the need for a new approach. Two different solutions that enable the complete use of the angular distribution information for the extraction of theZ parameters are presented. We show that these approaches have accuracies well above the future experimental needs.     

Properties of anomalous eμ events produced in e+e− annihilation

We present the properties of 105 events of the form e⁺ + e^? → e^+- + μ^? + missing energy, in which no other charged particles or photons are detected. The simplesthypothesis compatible with all the data is that these events come from the production of a pair of heavy leptons, the mass of the lepton being in the range 1.6 to 2.0 GeV/c²     

Toponium production in e+e− collisions

We study the properties of toponium states and their production in e⁺e^? collisions with special emphasis on the mass region accessible to SLC and LEP. A formalism for toponium -Z mixing is developed that is applicable for arbitrary mass differences between Z and the toponium state. It is shown that simple lowest-order perturbation theory is equivalent to the mixing formalism up to an accuracy better than one percent in the entire energy range we investigate. The results are illustrated by calculations performed in the framework of two QCD-inspired potential models which predict about 10 narrow states in the mass range around the Z. The mixing effects on the properties of Z are small even in the case of degenerate Z and toponium masses. The effect of electroweak interferences on and around toponium are studied, and analytic forms for cross sections and asymmetries before and after energy smearing are presented. We show that high radial excitations of toponium states below threshold may be difficult to disentangle from the continuum states. A brief survey of the properties of heavy bottom-type quarkonia concludes the paper.     

F-meson production in e+e− annihilation

The F-meson production rate is calculated on the ψ(4414) resonance using non-relativistic multipole expansion techniques. The results are compared with the available data.