摘要:

AbstractIn the spinel system Li1‐yTi2O4the Li content was reduced by oxidative extraction by means of a solution of I2as well as Br2in CH3CN or by oxygen. The extraction is associated with a transition of Ti3+to Ti4+: the system is Li1‐yTi3+1‐yTi4+1+yO4. Consequently, with increasingythe charge carrier concentration decreases from the starting value of 0.5 electrons/Ti ion for LiTi2O4. The extraction proceeds in two steps. At the beginning, the Ti2O4framework remains intact and the transition to superconductivity increases with decreasing charge carrier concentration to a maximal value of 13.2 K. Separated by a two‐phase region for medium extraction levels for higheryvalues, a Li depleted material of approximate composition Li0.3Ti2O4is obtained. The crystal structure of Li0.3Ti2O4can be deduced from the original spinel lattice by a partial Ti migration from 16dto 16cand 8asites (space group Fd3m). Consequently, the Ti2O4framework of Li0.3Ti2O4is disconnected and the material is no longer supercon

ISSN:0003-3804    

DOI:10.1002/andp.19935050803

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe show that a simple diffusion controlled growth, with subsequent aggregation, mean field theory accounts numerically for the growth of hydrogen clusters in certain metals (e.g. V, Nb, Zr, etc.). We also calculate the percolation threshold for the formation of an “infinite” aggregate both analytically and by a Monte Carlo simulation in a cubic lattice. The results are comparable and seem to correspond to the observed physical behav

ISSN:0003-3804    

DOI:10.1002/andp.19935050804

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe stochastic Schrödinger equation, a novel method for describing the dissipative dynamics of open quantum systems interacting with their environment, is applied to some nonlinear optical processes, namely nonlinear absorption and second‐harmonic generation, the latter also in the range of instabilities and classical chaotic behaviour. Where possible the results are compared with numerical simulations of the positivePrepresentation, which in some cases are found to give unreliable resul

ISSN:0003-3804    

DOI:10.1002/andp.19935050805

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe infinite set of cluster equations, proposed by Binder and Müller‐Krumbhaar for a Glauber kinetic Ising ferromagnet in 1974, generalize the Becker‐Döring equations used in classical nucleation theory. For positive symmetric transition rates satisfying certain growth conditions and a detailed balance condition we prove for sufficiently fast decaying initial cluster distributions the existence of a positive cluster distribution with finite density for all finite times solving the cluster equations. Uniqueness is proven under some further conditions on the transition rates. Our existence and uniqueness results apply e.g. for a Glauber kinetic Ising ferromagnet in two dimen

ISSN:0003-3804    

DOI:10.1002/andp.19935050806

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe coupling of antiferromagnetic spin excitations and propagating holes has been studied theoretically on a square lattice in order to investigate the dependence of antiferromagnetic order on hole doping, being of relevance, e.g., for the Cu–3d9system in antiferromagnetic CuO2‐planes of high‐Tcsuperconductors. An effective Hamiltonian has been used, which results from a 2D Hubbard model (hopping integralt) with holes and with strong on‐site Coulomb repulsionU. Bare antiferromagnetic excitations and holes with energies of the same order of magnitudet2/Uare interacting via a coupling term being proportional totand allowing holes to hop by emitting and absorbing spinwaves. In terms of a self‐consistent one‐loop approximation the renormalization of the spectral function both of holes and antiferromagnetic spin excitations are

ISSN:0003-3804    

DOI:10.1002/andp.19935050807

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19935050808

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19935050809

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19935050810

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19935050802

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY