Longitudinal spin relaxation in simple stochastic models for disordered systems

The relaxation of single probe spins was investigated for simple models of systems with quenched disorder. The spin relaxation was calculated for a two-site model with arbitrarily oriented magnetic fields and the result was averaged over various distributions of the fields, and of the hopping rates of the spin. On an intermediate time scale, a modified Kubo-Toyabe behavior is obtained for large hopping rates, in agreement with recent SR experiments. A stretched-exponential decay of the spin polarization is obtained at longer times. The Kohlrausch exponent is found to be field and hopping-rate dependent, in qualitative agreement with recent NMR and -NMR experiments. The resulting longitudinal relaxation rate still does not show the significant deviations from the Bloembergen-Purcell-Pound (BPP) behavior that are typical for glassy systems. Therefore, the random two-frequency model was extended to include time-dependent renewals of the environment. This modification may yield asymmetric peaks for the longitudinal relaxation rate in the BPP plot for very large renewal rates. © 1995 The American Physical Society

Diffusion in infinite and semi-infinite lattices with long-range coupling

We prove that for a one-dimensional infinite lattice, with long-range coupling among sites, the diffusion of an initial delta-like pulse in the bulk, is ballistic at all times. We obtain a closed-form expression for the mean square displacement (MSD) as a function of time, and show some cases including finite range coupling, exponentially decreasing coupling and power-law decreasing coupling. For the case of an initial excitation at the edge of the lattice, we find an approximate expression for the MSD that predicts ballistic behavior at long times, in agreement with numerical results.Comment: 4 pages, 5 figures, submitted for publicatio

Crystallite size dependent cation distribution in nanostructured spinels studied by nmr, mössbauer spectroscopy and XPS

Owing to the structural flexibility of spinels, providing a wide range of physical and chemical behavior, these materials have been considered as a convenient model system for the investigation of the size dependent properties of complex ionic systems. In this work, quantitative formation is obtained on the crystallite size dependent ionic configuration in nanosized spinel oxides prepared by mechanochemical processing of the corresponding bulk materials. Experimentally determined values of the crystallite size and of the mean degree of inversion of nanostructured spinels are used to calculate the volume fraction of interfaces/surfaces and their thickness in the nanomaterials

Multinuclear Solid-State NMR Study of Local Structure and Dynamics in Li0.7Nb3S4

The present work focuses on channel-structured Li0.7Nb3S4, where, among others, the question of the dimensionality of the diffusion pathway arises

Experimental evidence for the relaxation coupling of all longitudinal 7Li magnetization orders in the superionic conductor Li10GeP2S12

This contribution addresses the experimental proof of the relaxation coupling of the 7Li (I = 3/2) longitudinal magnetization orders in the solid-state electrolyte Li10GeP2S12 (LGPS). This effect was theoretically described by Korb and Petit in 1988 but has not yet been shown experimentally. In a 2D-T1/spin-alignment echo (SAE) experiment, the inverse Laplace transformation of the spectral component over two time dimensions revealed the asymmetric course of the spin-lattice relaxation following from the coupling of all longitudinal orders. These observations were supported by Multi-quantum-filter experiments and by simulations of the 2D-T1/SAE experiment with a lithium spin system. Since the asymmetric relaxation effects are directly dependent on the velocities and degrees of freedom of ion motion they could be used especially in fast Li-ion conductors as a separation tool for environments with different mobility processes

Nuclear Magnetic Resonance and Impedance Spectroscopy Studies on Lithium Ion Diffusion in γ-LiAlO2

In this work we show conductivity spectra of γ-LiAlO2 single crystals purchased from CrysTec and microcrystalline powder prepared by solid state synthesis