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根据研究模型首先得出压电陶瓷极化特性的理论推测,然后使用DP-5型介电谱仪,测量由压电陶瓷材料制作的蜂鸣器。实验测出压电陶瓷的极化方式与极化率和外场频率有关,随着频率的增加,压电陶瓷的离子位移极化率、电介质分子取向极化的极化率将减小,最终表现为相对介电常数减小。实验结果与理论猜测吻合。 相似文献
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利用不同功率密度的10.6 μm(光子能量为0.12 eV)连续激光辐照了禁带宽度为0.228 eV的光导型锑化铟探测器, 得到了与以往报道不同的实验现象. 当10.6 μm波段外激光辐照光导型探测器时, 探测器吸收激光能量后温度升高. 在探测器的温升过程中, 存在一个转变温度T0. 当探测器的温度T<T0时, 载流子浓度基本不变, 迁移率随温度的升高呈T-2.35趋势下降, 引起探测器的电导率减小, 电阻增大, 响应输出电压升高; 当T>T0时, 热激发载流子浓度随温度的升高呈指数增长, 电阻急剧下降, 超过了载流子迁移率降低对电阻的影响, 响应输出急剧下降. 光电导探测器在较高功率密度波段外激光辐照下的响应特性是载流子的浓度和迁移率在温度影响下相互作用的结果. 这对进一步完善半导体内载流子输运模型提供了实验依据. 相似文献
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研究了用HZ-B串列加速器的18MeV质子辐照对TiNi形状记忆合金R相变的影响,辐照在奥氏体母相状态下进行。示差扫描量热法(DSC)表明,辐照后R相变开始温度TsR和逆马氏体相变结束温度TfA随辐照注量的增加而降低。当注量为1.53×1014/cm2时,TsR和TfA分别下降6K和13K,辐照未引起R相变结束温度TsR和逆马氏体相变开始温度TfA的变化。表明辐照后母相(奥氏体相)稳定。透射电镜(TEM)分析表明辐照后没有引起合金可观察的微观组织变化。辐照对R相变开始温度TsR和逆马氏体相变结束温度Af的影响可能是由于质子辐照后产生了孤立的缺陷团,形成了局部应力场,引起晶格有序度的下降所造成的。 相似文献
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获得覆盖较宽温度和压力范围内的等离子体输运性质是进行等离子体传热和流动过程数值模拟的必要条件.本文采用Saha方程计算等离子体组分, 采用基于将Chapman-Enskog方法扩展到高阶近似的方法, 计算获得了电子温度(Te)不等于重粒子温度(Th)的情形下, 在300 K到40000 K的温度范围内氦等离子体的黏性、热导率和电导率. 研究结果表明压力和热力学非平衡参数(θ =Te/Th)对氦等离子体的输运性质有较大的影响. 在局域热力学平衡条件下,计算获得的氦等离子体输运性质和文献报道的数据符合良好. 相似文献
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B. S. Tewari A. Dhyani . Ajay 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):67-74
The influence of inter unit cell resonant tunneling between the
copper-oxygen planes on the c-axis electronic conductivity (σc) in
normal state of optimal doped bilayer high Tc cuprates like
Bi2Sr2CaCu2O8+x is investigated using extended Hubbard
Hamiltonian including resonant tunneling term (T12) between the planes
in two adjoining cells. The expression for the out-of-plane (c-axis)
conductivity is calculated within Kubo formalism and single particle Green's
function by employing Green's function equations of motion technique within
meanfield approximation. On the basis of numerical computation, it is
pointed out that the renormalized c-axis conductivity increases exponentially with the increment in inter cell
resonant tunneling. The effect of T12 on renormalized c-axis
conductivity is found to be prominent at low temperatures as compared to
temperatures above room temperature (~300 °K). The Coulomb
correlation suppresses the variation of renormalized c-axis conductivity
with temperature, while renormalized c-axis conductivity increases on
increasing carrier concentration. These theoretical results are viewed in
terms of existing c-axis transport measurements. 相似文献
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U. Poschinger A. Walther M. Hettrich F. Ziesel F. Schmidt-Kaler 《Applied physics. B, Lasers and optics》2012,107(4):1159-1165
We present a detailed theoretical and experimental study on the optical control of a trapped-ion qubit subject to thermally induced fluctuations of the Rabi frequency. The coupling fluctuations are caused by thermal excitation on three harmonic oscillator modes. We develop an effective Maxwell–Boltzmann theory which leads to a replacement of several quantized oscillator modes by an effective continuous probability distribution function for the Rabi frequency. The model is experimentally verified for driving the quadrupole transition with resonant square pulses. This allows for the determination of the ion temperature with an accuracy of better than 2% of the temperature pertaining to the Doppler cooling limit T D over a range from 0.5T D to 5T D . The theory is then applied successfully to model experimental data for rapid adiabatic passage (RAP) pulses. We apply the model and the obtained experimental parameters to elucidate the robustness and efficiency of the RAP process by means of numerical simulations. 相似文献
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A Green's function model for ferromagnetism and spin excitations of (Ga,Mn)As diluted magnetic semiconductors
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We study (Ga, Mn)As diluted magnetic semiconductors in
terms of the Ruderman--Kittel--Kasuya--Yosida quantum spin model in
Green's function approach. Random distributions of the magnetic
atoms are treated by using an analytical average of magnetic
configurations. Average magnetic moments and spin excitation spectra
as functions of temperature can be obtained by solving
self-consistent equations, and the Curie temperature TC is
given explicitly. TC is proportional to magnetic atomic
concentration, and there exists a maximum for TC as a
function of carrier concentration. Applied to (Ga, Mn)As, the
theoretical results are consistent with experiment and the
experimental TC can be obtained with reasonable parameters.
This modelling can also be applied to other diluted magnetic
semiconductors. 相似文献
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The phase transitions to an ordered state in three-dimensional polymer systems that consist of flexible and rigid segments with intrachain and interchain orientational-deformational dipole interactions are considered. The statistic properties of the proposed models correspond to the Gaussian and spherical approximations that are used to describe the behavior of anisotropic Heisenberg ferroelectrics and ferromagnets. In the three-dimensional models under consideration, there exists a critical point T c where a secondorder phase transition from an isotropic state to a state with long-range orientational order occurs. The laws of variation in the temperature T c as a function of anisotropy of the interactions are established by analytical methods. The temperature dependences of the long-range dipole order parameter for a given chain bending are calculated and the results are compared with the experimental data obtained by the piezoelectric pressure step (PPS) method for thick ferroelectric PVDF and P(VDF-TrFE) polymer films. 相似文献
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Piezoelectric and dielectric investigations have been performed on a (PMN)0.69(PT)0.31 single crystal. Low frequency (100?Hz) dielectric permittivity measurements revealed distinct anomaly at 129°C (T εmax) corresponding to the structural transformation from the tetragonal to cubic phase. Two other anomalies have been detected at 90 and 96°C. After preliminary polarization in the d.c. electric field, switched on above T εmax and switched off inside the tetragonal phase, the piezoelectric activity has been observed in function of temperature. Values of the piezoelectric resonance frequencies changed markedly at 96°C (on cooling) and 124°C (on heating) showing clear softening of the elastic properties near these temperatures. Values of the piezoelectric and electromechanical coupling coefficients obtained were respectively of the order of 800?pCN?1 (d 31) and 0.35?(k 31). Piezoelectric activity was detected tens of degrees above the temperature T εmax and disappeared at temperature at which the dispersion of the dielectric permittivity due to the presence of polar nanoregions is negligible. It was found that strong softening of the elastic properties accompanies phase transitions to the tetragonal and monoclinic phase. 相似文献
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The theoretical investigation of the superconducting state properties viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T C, isotope effect exponent α and effective interaction strength N 0 V of ten binary CuCZr100-C (C = 25–60 at%) metallic glasses is performed, using Ashcroft’s empty core model potential. Five local-field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used to study the screening influence on the aforesaid properties. It is shown that the electronphonon coupling strength λ and the transition temperature T C are quite sensitive to the selection of the local-field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N 0 V show a weak dependence on the local-field correction functions. The values of T C obtained from the H-local-field correction function are found to be in qualitative agreement with available theoretical or experimental data and show almost linear behavior with respect to the concentration C of Cu. The present results are shown to be in good agreement with other available theoretical or experimental data. The obtained results confirm the existence of the superconducting phase in the metallic glasses. 相似文献
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The temperature dependence of the intracrystallite conductivity of Langmuir-Blodgett films of the (C16H33-TCNQ)0.4(C17H35-DMTTF)0.6 charge-transfer complex (CTC) is studied by measuring the surface acoustic wave attenuation in a piezoelectric delay line coated with such a film. (C16H33-TCNQ)0.4(C17H35-DMTTF)0.6 is a surface-active CTC made from a 1.5: 1 mixture of heptadecyl-dimethyltetrathiafulvalene (C17H35-DMTTF) and hexadecyl-tetracyanoquinodimethane (C16H33-TCNQ). The temperature dependence of the intracrystallite conductivity is found to have a maximum at TMD=193.5 K. Above TMD, the conductivity of the films is metallic (?σ/?T<0), while below this temperature it obeys a law that is close to the one-dimensional Mott law. The decrease in the conductivity with decreasing temperature at T<TMD is shown to be related to the localization of electron states in the quasi-one-dimensional system under study and to be caused by the presence of impurities and defects in the TCNQ chains, along which a charge is transferred. The detected variation in the conductivity with temperature below TMD is found to qualitatively and quantitatively agree with the model of localization in a weakly disordered quasi-one-dimensional system proposed earlier by Nakhmedov, Prigodin, and Samukhin. Fitting the experimental results to the theoretical dependences obtained in the framework of this model allows us to find the electron-phonon and electron-impurity scattering times. The structural parameters of the conducting layer are used to estimate the density of states at the Fermi level and the Fermi velocity in the films. With these values, the mean free path and the localization length in the films under study are determined. 相似文献
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A. V. Klochkov V. V. Kuz’min K. R. Safiullin M. S. Tagirov D. A. Tayurskii N. Mulders 《JETP Letters》2008,88(12):823-827
The spin kinetics of 3He in an aerogel has been studied above the Fermi temperature. The magnetic relaxation times T 1 and T 2 of adsorbed, gaseous, and liquid 3He in a 95% silica aerogel at a temperature of 1.5 K have been determined as functions of frequency by means of pulse nuclear magnetic resonance. It has been found that the time T 1 is linear in frequency in all three cases, whereas T 2 is independent of frequency. To explain the observed behavior of the longitudinal relaxation rate, a theoretical model of relaxation in the adsorbed layer of 3He taking into account the filamentary structure of the aerogel is proposed. 相似文献
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可调频率压电换能器原理 总被引:3,自引:0,他引:3
最近,我们曾研究电负载对压电振动系统振动特性的影响[1,2]。随着电负载的连续变化,通过压电效应,压电振动系统的谐振频率也连续地改变。由此引伸,可以实现可调频率压电换能器,本文将对其原理进行研讨。
我们将对压电夹心换能器进行这种调节频率的理论分析,并对一种纵向加电场,纵向振动的夹心换能器进行实验比较。理论与实验结果一致表明,用有效耦合系数Keff来衡量,该换能器可以在一个半倍频程的范围内有效地工作。
这里提出的可调频率压电换能器,由于是改变电负载,通过压电耦合来实现换能器的频率调节的,因此它还具有方便、连续和瞬时可调的特点。 相似文献
我们将对压电夹心换能器进行这种调节频率的理论分析,并对一种纵向加电场,纵向振动的夹心换能器进行实验比较。理论与实验结果一致表明,用有效耦合系数Keff来衡量,该换能器可以在一个半倍频程的范围内有效地工作。
这里提出的可调频率压电换能器,由于是改变电负载,通过压电耦合来实现换能器的频率调节的,因此它还具有方便、连续和瞬时可调的特点。 相似文献
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对三明治复合结构TbxDy1-xFe2-y/Pb(Zr, Ti)O3/TbxDy1-xFe2-y的电容与频率及磁场的函数关系进行了实验和理论研究. 实验发现,该复合材料样品的电容随频率的增加而出现多个谐振峰,并且其谐振点随磁场的增加而发生频移. 在谐振点附近,观察到样品的阻抗随磁场的增加由容抗性转变为感抗性,从而同时观察到巨大的正磁电容效应和负磁电容效应. 由复合材料的弹性力学本构方程出发,对该类样品的电容随频率及磁场的变化进行了理论模拟. 结果显示,模拟曲线与实验结果符合得很好. 理论表明该磁致伸缩/压电复合材料的磁电容效应源于磁场诱变的铁磁相柔顺系数.
关键词:
层状复合材料
界面弹性耦合
磁电容效应 相似文献