共查询到20条相似文献,搜索用时 93 毫秒
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利用线性组合算符和幺正变换相结合的方法,研究了声子色散对极性晶体中磁极化子基态能量的影响.计及纵光学(LO)声子色散,在抛物近似下导出了极性晶体中磁极化子基态能量随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数的变化关系.数值计算结果表明磁极化子基态能量随声子色散系数和电子-纵光学声子耦合常数的增大而减小,随回旋共振频率增大而增大. 相似文献
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利用线性组合算符和幺正变换相结合的方法,研究了声子色散对极性晶体中磁极化子基态能量的影响。计及纵光学(LO)声子色散,在抛物近似下导出了极性晶体中磁极化子基态能量随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数的变化关系。数值计算结果表明磁极化子基态能量随声子色散系数和电子-纵光学声子耦合常数的增大而减小,随回旋共振频率增大而增大。 相似文献
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T. Kala 《Phase Transitions》2013,86(1-4):65-88
The theoretical backgrounds and some experimental data on the electronic properties of polycrystalline Pb(Zr, Ti)O3 solid solutions are summarized. These substances occur in the perovskite structure, and so their electronic band structure is presumed to be analogous to other perovskite compounds. Their forbidden gap energy has been determined to be about 3.30–3.56 eV on the basis of optical, photoacoustical, and photoelectrical measurements. Many local levels and traps exist in the forbidden gap because of the polycrystalline character and heterovalent doping. Their actual configurations and states strongly influence the optical, photoelectrical, piezoelectrical, and other physical properties of Pb(Zr, Ti)O3 solid solutions. 相似文献
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G. Onori 《Il Nuovo Cimento D》1986,8(5):465-480
Summary The adiabatic compressibility of ethanol-water mixtures was measured as a function of temperature and cosolvent concentration;
the measurements were carried out at 5°C intervals over the range (10⋎40) °C, paying particular attention to the water-rich
region (mole fraction of cosolventx
2<0.25). The observed concentration dependencies of the adiabatic compressibility in the low-concentration range were well
explained if we consider the existence in the mixture of local structures with a composition that is close to ethanol-17 H2O like that of solid clathrate hydrate of type II. A simple model, involving the solutesolvent interactions and the molecular
aggregation of the solute, is used to explain the observed behaviour.
To speed up publication, the author of this paper has agreed to not receive the proofs for correction. 相似文献
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S. J. Candau P. Hebraud V. Schmitt F. Lequeux F. Kern R. Zana 《Il Nuovo Cimento D》1994,16(9):1401-1410
Summary Both linear and non-linear viscoelasticity experiments have been performed in semi-dilute micellar aqueous solutions of ethanediyl-α,ω-bis
(dodecylmethylammonium bromide) as a function of solution chloride (NaCl) concentration. The results suggest that both linear
and non-linear properties are affected by the electrostatic interactions. In particular, the plateau modulusG′∞ and the ratioσ
m/G′∞, whereσ
m represents the plateau value in a stress-shear rate experiment, are enhanced as the electrostatic interactions are screened
by addition of salt. The zero-shear viscosity is lowered upon addition of NaCl, due likely to an exchange of the Cl− ions with the Br− counterions.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
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The relaxation of a one-dimensional magnetic nanoparticle linear chain with lattice constant $a$ is investigated in absence of applied field. There is an equilibrium state (or steady state) where all magnetic moments of particles lie along the chain (x-axis), back to which the magnetic nanoparticle chain at other state will relax. It is found that the relaxation time Tx is determined by Tx=10β× a3. This relaxationis compared with that of single magnetic nanoparticle system. 相似文献
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Summary The optical properties of conductive transparent thin films of undoped SnO2, prepared by using magnetron supttering, were studied by measuring the transmittance and the reflectance between λ=0.25 μm
and λ=3μm. The extracted optical constants are interpreted to give values of a direct band gap of the order of 4 eV and of
an indirect band gap of the order of 3 eV. Typical SnO2 films transmit ≈85% of visible light, have sheet resistanceR
∂ (100÷800) Ω∂ and resistivities of (2.4·10−3÷1.8·10−2) Ω cm.
Riassunto Mediante la misura dei valori di transmittanza e di riflettanza per lunghezze d'onda comprese fra 0.25 μm e 3 μm, sono state studiate le proprietà ottiche di film sottili (trasparenti e conduttivi) di SnO2 non drogato, preparati mediante sputtering. Dai valori così ottenuti sono stati ricavati valori del gap diretto dell'ordine di 4 eV e di quello indiretto dell'ordine di 3 eV. Un film di SnO2 presenta tipicamente valori della transmittanza intorno all'85%, per luce visibile,R ∂ intorno ai (100÷800) Ω∂ e resistività fra 2.4·10−3 e 1.8·10−2 Ω cm.
Резюме Пзмеряя величины пропускания и отражения в области длин волн между λ=0.25 мкм и λ=3 мкм, исследуются оптические свойства проводящих прозрачных тонких пленок нелегированного SnO2, приготовленных с помощью напыления. Из полученных оптических постоянных извлекаются значения прямой щели, порядка 4 эВ, и непрямой щели, порядка 3 эВ. Типичные пленки SnO2 пропускают ∼85% видимого света, имеют сопротивлениеR ∂ (100÷800) Ω∂ и удельные сопротивления в области (2.4·10−3÷1.8·10−2) Ом·см.相似文献
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A. C. Felici N. Galbato D. Debowska T. Papa M. Piacentini F. Lama 《Il Nuovo Cimento D》1994,16(2):163-168
Summary We have measured at room temperature the photoacoustic spectra of Cd1−x
Fe
x
Te(0<x<0.055) around the CdTe fundamental absorption threshold. We identified an absorption band at (1.38±0.01) eV, increasing with
the Fe concentration, that we assigned to the5
E→3
T
1 transition within the Fe2+ (3d
6) manifold. We observed also a broadening and a shift to higher energies of the CdTe absorption edge for increasingx.
Work partially supported by the Italian Consorzio INFM and CNR through the GNSM. 相似文献
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Summary The theory of the RPA optical response of a solid has been generalized in order to take into account also the possible presence
of spatially nonlocal potentials in the Hamiltonian. Explicit expressions for first- and second-order susceptibilities are
given in the new framework. The expressions obtained depend on the matrix elements of operators of the form of a commutator
of a component of the position operatorr and an operator that commutes with the lattice translations. The problem of the evaluation of these matrix elements is solved
in a simple manner by introducing an auxiliary, periodic position operator,XXXr. In such a way a general formulation is obtained that preserves the gauge invariance. As an application of the new theory,
the second harmonic generation (SHG) from a semiconductor in a simple two-band model has been studied. The differences between
our correct gauge-invariant results and those obtained in the usual local approximation is an indication of a slow convergence
of the expressions obtained in the local approximation. 相似文献
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Summary We have studied the behaviour of photoacoustic response of implanted silicon samples in order to measure the thermal conductivity
of damaged layers; the results allow us to determine such a parameter simply by the phase difference measurement between implanted
and unimplanted regions of the sample.
Riassunto è stata studiata la risposta fotoacustica di campioni di silicio impiantato allo scopo di misurare la conducibilità termica degli strati danneggiati; i risultati permettono di determinare questa grandezza misurando semplicemente la differenza di fase tra la zona impiantata e quella cristallina del campione.
Резюме Исследуется поведение фотоакустического отклика на образцах имплантированного кремиия, чтобы измерить теплопроводность поврежденных слоев. Полученные результаты позволяют получить величину теплопроводности с помощью измерения разности фаз между имплантированной и неимплантированной областлми образца.相似文献
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固相法制备了碱土金属铝酸盐荧光粉CaAl12O19 : Eu,Mn,测试了样品的XRD及激发与发射光谱,对样品的结构及其发光性能进行了分析,并且考察了灼烧温度及Eu3+的浓度对样品发光性能的影响,对Eu3+的作用机理进行了探讨。 该荧光粉能被波长短于550 nm的蓝绿光以及紫外和近紫外光激发,其发射光谱峰值在590,615,645,657 nm,其中前两个为Eu3+的特征发射,后两个为Mn4+的2E-4 A2跃迁发射。该荧光粉的最佳烧结温度与时间分别为1 550 ℃和4 h,Eu3+的最佳掺杂摩尔分数为0.11%左右。 相似文献
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利用基于密度泛函理论的第一性原理平面波赝势方法 并结合准谐徳拜模型研究了NaCl结构的TiC在高压下的弹性性质、电子结构和热力学性质. 计算所得零温零压下的晶格常数、体弹模量及弹性常数与实验值符合得很好. 零温下弹性常数和弹性模量随压强增大而增大. 通过态密度和电荷密度的分析, Ti-C键随压强增大而增强. 运用准谐德拜模型, 成功计算了TiC在高温高压下的体弹模量、熵、热膨胀系数、徳拜温度、 Grüneisen参数和比热容. 结果表明压强对体弹模量、热膨胀系数和徳拜温度的影响大于温度对其的影响. 热容随着压强升高而减小, 在高温高压下, 热容接近Dulong-Petit极限. 相似文献