非晶态快离子导体电导特性的低频弛豫理论

结合快离子导体玻璃的结构特点和倪嘉陵(Ngai)的低能激发、弛豫、耗散统一理论,依据非Markov方程探讨了快离子的输运特点,导出了非晶态快离子导体电导的频率-温度依赖关系。理论方法与现有快离子导体电导理论不同,结果表明与实验数据符合较好,理论能较好地描述低温下电导的色散现象。色散的程度与表征物质内部结构差异的参数——红外发散指数n有关。 关键词：     

非晶态快离子导体电导特性的低频弛豫理论

结合快离子导体玻璃的结构特点和倪嘉陵(Ngai) 的低能激发、弛豫、耗散统一理论, 依据非Markov 方程探讨了快离子的输运特点, 导出了非晶态快离子导体电导的频率一温度依赖关系. 理论方法与现有快离子导体电导理论不同, 结果表明与实验数据符合较好, 理论能较好地描述低温下电导的色散现象. 色散的程度与表征物质内部结构差异的参数— 红外发散指数n有关. 关键词：     

快离子导体的低频介电特性

本文综述了快离子导体低频介电特性的实验规律,介绍和讨论了近年来提出的几个关于快离子导体介电特性的理论模型,并将实验结果与经验公式、理论模型进行了比较。     

快离子导体的低频介电特性

本文综述了快离子导体低频介电特性的实验规律,介绍和讨论了近年来提出的几个关于快离子导体介电特性的理论模型,并将实验结果与经验公式、理论模型进行了比较。     

快速C60离子团在固体中的库仑爆炸过程Ⅱ——分子动力学模拟

研究了快速Ｃ₆₀离子团与固体材料的相互作用过程.借助于线性介电响应理论及等离子-极点近似介电函数,推导出作用在团簇中单个离子上的动力学相互作用力,并建立了一套描述离子团中单个离子运动的方程组.通过数值求解运动方程组,可以发现,对于高速Ｃ₆₀离子团在固体中穿行时,由于动力学相互作用力的影响,使得库仑爆炸图形呈现出很强的非球对称性,即离子团中的导航离子群爆炸得较快,而尾随离子群则保持相对地稳定. 关键词： 离子团 库仑爆炸 动力学相互作用     

弛豫型铁电体铌镁酸铅陶瓷的玻璃化行为研究

钛酸铅与铌镁酸铅组成比为1:9的固溶体陶瓷是典型的弛豫型铁电体,其介电行为与偶极玻璃的介电行为极为相似,并已将玻璃学中的Vogel-Fulcher关系用于处理其介电常数峰值温度与频率的关系。本文测定了其介电行为随温度的变化,对其微观局域极化行为进行了分析,讨论了其局域极化的产生、增大及冻结过程,研究了弛豫型铁电体与Debye介质、玻璃体的关系和区别。在此基础上,提出了一个更合理的函数关系式,用以表征其介电常数峰值温度与频率的关系,并得出其介电弛豫激活能为0.037eV。实际应用表明,对于弛豫型铁电体,该函数关系较原有Vogel-Fulcher关系更有效。 关键词：     

非晶态Cu+导体分相和晶化行为的XRD和SEM研究

对非晶态Cu⁺快离子导体0.4CuI-0.3Cu₂O-0.3P₂O₅在等温热处理条件下测量离子电导率的同时,进行了X射线衍射(XRD)与扫描电子显微术(SEM)研究。结果表明:初始的非晶态材料是分相的;随着等温热处理,分离的非晶第二相逐渐消失,并发生非晶态晶化;晶态的γ-CuI与Cu₂P₂O₇先后析出,逐渐长大。此材料的分相和晶化行为同电导率反常性的对应,再一次证实了非晶态快离子导体中的相界效应及其普遍意义。 关键词：     

Fe-Ni-BaTiO3复合材料的介电行为及其机理研究

利用金属铁、镍(Fe与Ni保持mol比为22∶78不变)与钛酸钡复合，在保护气氛下成功烧结制备了高介电常数Fe-Ni-BaTiO₃复合陶瓷材料，并研究了该复合材料的电导和介电性能及其物理机理.分析结果表明，由于渗流效应，随着陶瓷中金属含量的增加，材料经历了绝缘体—导体突变.同时，在渗流阈值附近，材料的介电常数有了极大的提高.当金属体积含量为0.23时，即在绝缘体向导体转变的渗流阈值附近，复合材料的介电常数达到了22000，为同条件下制备的纯钛酸钡陶瓷体介电常数的12倍，同时材料的介电 关键词： 3')" href="#">Fe-Ni-BaTiO₃ 渗流理论 介电性能 Maxwell-Wagner效应     

快离子导体的物理研究

快离子导体(也称为超离子导体或固体电解质)是指那些离子电导率接近或超过熔盐(或电解质溶液)的一类固体材料。 近十几年来,人们对快离子导体进行了相当广泛的研究。日前这种研究的兴趣正在进一步增长。快离子导体物理学或固体离子学将成为凝聚态物理学的一个重要分支。 本文概述了快离子导体物理的研究现状。全文包括基本概念、实验测量和理论研究三部分。 基本概念部分的主要内容有:快离子导体的分类,结构条件,亚晶格熔化,动态特征,热力学讨论和模型哈密顿量。 实验测量部分的主要内容有:结构研究,电导率测量,非弹性光散射,核磁共振研究和其它物理性质的临界行为(如比热和声学性质)。 理论研究部分的主要内容有:晶格气体模型,连续随机模型和快离子导体中的相变。     

快离子导体的物理研究

快离子导体(也称为超离子导体或固体电解质)是指那些离子电导率接近或超过熔盐(或电解质溶液)的一类固体材料。 近十几年来,人们对快离子导体进行了相当广泛的研究。日前这种研究的兴趣正在进一步增长。快离子导体物理学或固体离子学将成为凝聚态物理学的一个重要分支。 本文概述了快离子导体物理的研究现状。全文包括基本概念、实验测量和理论研究三部分。 基本概念部分的主要内容有:快离子导体的分类,结构条件,亚晶格熔化,动态特征,热力学讨论和模型哈密顿量。 实验测量部分的主要内容有:结构研究,电导率测量,非弹性光散射,核磁共振研究和其它物理性质的临界行为(如比热和声学性质)。 理论研究部分的主要内容有:晶格气体模型,连续随机模型和快离子导体中的相变。     

Collective motion in superionic conductors

A theory of collective motion in superionic conductors is described by the use of a model of a crystalline cage immersed in a viscous liquid. The viscoelastic force and the interionic Coulomb force are considered as the cage—liquid interaction. The density-correlation functions and the frequency-dependent conductivity are calculated. The calculated conductivities for α-AgI are in good agreement with experiments. It is concluded that the structure in a.c. conductivity experimentally observed for α-AgI at frequencies below 10 cm^-1 can be ascribed to acoustic phonons.     

Simulation of prefactor anomalies in superionic conductors in the case of arbitrary energy losses

Based on a sticking-probability formulation, we have considered a breakdown of absolute rate theory in relation to prefactor anomalies in superionic conductors in the case of arbitrary energy losses of ions. We present simulation results concerning the prefactor dependence on the magnitude of the average energy loss in the energy-transfer range from 10⁻³ to 0.46 kT and the energy dependence of the sticking probability for ions.     

Frequency-dependent spin-lattice relaxation study of transport processes in superionic conductors

The sensitivity of the¹⁹F spin-lattice relaxation dispersion, T₁,(ω), to motional disorder in crystalline superionic conductors of the type La_1?xSr_xF_3?x (x = 0; 0.03) is shown. T₁ times are measured in the frequency range from 90 kHz to 370 MHz using standard techniques in combination with field-cycling. The relaxation dispersion shows qualitative differences from the standard Bloembergen-Purcell-Pound behavior. At low frequencies a relaxation model using a distribution of correlation times for diffusing ions is found to be consistent with the experimental results. At frequencies higher than 50 MHz another process of the Debye type which is not induced by ionic hopping dominates the relaxation.     

Breakdown of absolute rate theory and prefactor anomalies in superionic conductors

We suggest that the anomalously low prefactors observed for the ionic hopping rate in defect-structure superionic conductors are due to a breakdown of absolute rate theory. A treatment that takes dissipative processes into account is introduced and a new expression for the prefactor is obtained. We present NMR data on the superionic conductor Li₂Ti₃O₇ that supports these ideas and extract the value of the elemental energy transfer per collision.     

A model for the heat of transport in ionic conductors

The ion flow caused by a temperature gradient originates the ionic thermopower which is quantified by the heat of transport. Experimentally, it is known that in superionic conductors, the heat of transport Q is nearly equal to the activation energy for ion transport E_a. In the present paper, a model for the heat of transport in ionic conductors has been proposed based on a lattice dynamical theory of diffusion. We have shown that the relationship between Q and E_a is determined by the participation degree of different phonon modes, in particular the short wavelength phonons to the atomic jump processes. The implication of this finding to the transport properties of superionic conductors has been discussed, and it is suggested that the degree of the collective motion in ionic conductors increases with the increase in Q/E_a. The model predicts that good ionic conductors will show large value of Q/E_a. The importance of the acoustic phonons in the ion transport processes has been also pointed out.     

Low-frequency,coulomb-correlated density fluctuations in superionic conductors and their influence on the conductivity

The low-frequency density and current response of diffusing ions is calculated for superionic conductors. In particular, it is shown that the peculiar dispersion of the conductivity of α-AgI at low frequencies is due to the scattering of silver ions by slowly relaxing local density fluctuations caused by the other silver ions.     

Hydrodynamics of superionic conductors

Using the Mori method we present a rigorous hydrodynamic theory for the collective excitations in superionic conductors at low frequencies and long wavelengths. By means of static and dynamic linear response theory all microscopic quantities of the theory are expressed as derivatives of the free energy or as transport coefficients. Explicit expressions for the dispersion and the damping of the modes and for the density correlation function are worked out for high-symmetry directions and numerically evaluated for-AgI. In particular we show that the two non-propagating modes can give rise to a small central component (width~k ², constant intensity) and a broad central component (constant width fork0, intensity ~k ²) in scattering spectra. Extrapolating our theory to larger wave vectors we offer a new explanation for the broad central component found recently in neutron scattering spectra of-AgI.     

快离子导体玻璃滞弹性弛豫的红外发散响应

本文依据Ngai(倪嘉陵)的低频激发、弛豫、耗散理论和非晶态快离子导体的特点,提出了非晶态快离子导体的滞弹性弛豫理论。认为快离子导体玻璃中的超声吸收主要来源于与玻璃网络呈微弱联系的快离子的热激活弛豫及伴之而来的低能激发的损耗。理论成功地描述了超声吸收的频率、温度依赖关系,解释了弛豫时间分布理论所不能解释的快离子导体玻璃的实验特征。     

Raman and far IR studies on Ag2CdI4 and Cu2CdI4 superionic compounds

Raman spectral studies, far infrared reflection and transmission spectra for the superionic conductors Ag₂CdI₄, Cu₂CdI₄ at 300 K are reported. From these studies the TO and LO modes are assigned and optical conductivity in the region 30 cm^-1-150 cm^-1 are calculated. The behaviour of conductivity in this frequency region is explained on the basis of jump diffusion model.     

Molecular dynamics simulation of the superionic conductor BaF2

Molecular dynamics simulations of the BaF₂ fluoride crystal were carried out over a wide range of temperatures in order to study structural and transport characteristics in the low-temperature, the high-temperature superionic, and the molten state. The experimental temperature dependence of the lattice constant was taken into account. A sharp change in total energy of the system in the vicinity of T=1200 K indicates a phase transition to the high-temperature state with a transition energy U=(18.8±0.2) kJ/mol which is close to the value of the latent heat Q=18.36 kJ/mol obtained experimentally at 1275 K. Calculation of the radial distribution functions g(r) shows that in the high-temperature superionic state the F^– sublattice is already disordered while the Ba²⁺ sublattice stays regularly ordered, which keeps the crystal in the solid state. In the low-temperature state both sublattices are regularly ordered, and in the molten state both sublattices are disordered. The calculated diffusion constants of F^– in the superionic state is about 10^–9m²/s which is a typical value for superionic conductors. The temperature dependence of the diffusion constant obeys the Arrhenius equation. Higher statistical moments of the trajectories are used to characterise the type of ion movement.