Off-centre Ions Research Articles

Density functional pseudopotential study of the endohedral complex Li 2@C 60

The spherically averaged pseudopotential (SAPS) model for treating the electronic structure and the energetics of a cluster of atoms is extended to allow use of first principles norm-conserving pseudopotentials including some nonlocality. The main theoretical development is the spherical average about the chosen cluster centre of an s-wave projection operator associated with an off-centre ion which results in an additional radially nonlocal term in the radial Schrödinger equation. However, much of the simplicity of the SAPS model is preserved. The approach is used to study the electronic structure and the energetics of Li 2@C 60. Self-consistent electron densities are obtained for the spherically averaged pseudopotentials corresponding to this endohedral complex and its component Li 2 and C 60 parts. The atoms are then allowed to relax their positions to minimize the total energy. In the cases of Li 2 and C 60 considerable improvement is achieved over calculations using the SAPS model with local pseudopotentials. Two minimum energy configurations are found for the Li 2 encapsulated inside a C 60 molecule. That with the longer LiLi bond length is the higher in energy by 0.88 eV and is marked by almost complete charge transfer from the Li 2 to the C 60 cage. The other more stable isomer shows little charge transfer but there is a noticeable build up of charge between the Li 2 and the C 60.

The possibility of Li+ off-centre ion tunnelling in K1-xLixTaO3 studied by second-harmonic generation

Time-dependent second-harmonic generation experiments in K1-xLixTaO3 crystals for the first time yield a Li concentration dependence of the activation energy of the Arrhenius-like reorientation process of the Li+ ions. The experimental data support the assumption of a Li+ off-centre ion tunnelling via excited and ground vibrational states. With increasing Li concentration, the tunnelling reorientation is suppressed in favour of a thermally activated over-barrier hopping. The suppression of the tunnelling reorientation can be explained by a model of cooperative tunnelling in a percolation dipole cluster and destruction of the tunnelling resonance condition by internal electric dipole fields.

An ESR Study of Li+ Impurity Ion Deformational Fields in KTaO3

AbstractFrom a study of the influence of uniaxial pressure on the ESR spectrum of “cubic” paramagnetic Fe3+ centres in KTaO3, their spin—phonon coefficients G11 = 1.28 × 10−3 eV and G44 ⪅ 0.74 × 10−4 eV are determined. The dilatation part of the deformation tensor Ω1 = 1.4 eV of the Li+ off‐centre ion in KTaO3 is obtained as a result of the study of the elastic broadening of the ESR line caused by the deformation fields of the Li+ ions. It is shown that the deformation mechanism makes a substantial contribution to the ESR linewidth of these centres in K1−xLixTaO3.

An electro-optical study of relaxation rates of off-centre ions in SrO

The rate of relaxation between off-centre sites of Ni 2+ and Co 2+ substitutional defects in SrO is determined from the response of the optical absorption to an electric field. This is achieved not by direct lifetime measurement but by an alternative and sensitive technique in which the optical signal is monitored exactly out of phase with a modulated electric-field. It is found that the temperature dependence of relaxation lifetimes in the range 70μs to 13ms for Ni 2+ ions is consistent with a simple classical thermally-activated process, a result which is to be held in contrast with the situation for Co 2+.

Local fields and electric dipole moment of localized impurities in crystals

Dipole transition matrix elements of impurity centres are estimated accounting for the “acting” electric field in the crystal Ea. Ea is shown to depend on the type of wave functions and radii of states among which the transition occurs. Some examples where Ea is essential are considered. It is found, for example, that the dipole moment of the localized electron is expressed via oscillator forces submitted to the sum rule only in the case when the radius of electron state is large enough. A corresponding criterion is given. The examination of matrix elements in the dipole transitions of off-centre ions shows that in this case the acting field is near to the Lorentz field. [Russian Text Ignored].

Paraelastic resonance of Jahn-Teller and off-centre ions

physica status solidi (a)Volume 15, Issue 2 p. K145-K147 Short Note Paraelastic resonance of Jahn-Teller and off-centre ions M. D. Glinchuk, M. D. Glinchuk Institute of Material Science, Academy of Sciences of the USSR, KievSearch for more papers by this authorA. A. Karmazin, A. A. Karmazin Institute of Material Science, Academy of Sciences of the USSR, KievSearch for more papers by this author M. D. Glinchuk, M. D. Glinchuk Institute of Material Science, Academy of Sciences of the USSR, KievSearch for more papers by this authorA. A. Karmazin, A. A. Karmazin Institute of Material Science, Academy of Sciences of the USSR, KievSearch for more papers by this author First published: 16 February 1973 https://doi.org/10.1002/pssa.2210150261Citations: 1AboutRelatedInformationPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessClose modalShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume15, Issue216 February 1973Pages K145-K147 RelatedInformation RecommendedElectron Paramagnetic Resonance Study of the Dynamical Jahn-Teller Effect on the 3d1 Impurities Ti3+ and V4+ in GaPJ. Kreissl, W. Ulrici, W. Gehlhoff, physica status solidi (b)EPR of Gd ions in Jahn-Teller-distorted rare-earth crystals TbAsO4, TmAsO4, and TmVO4G. Schwab, physica status solidi (b)Fundamentals of Electron Spin Resonance (ESR)Nitroxides: Applications in Chemistry, Biomedicine, and Materials Science, [1]Electron Paramagnetic Resonance SpectroscopyGunnar Jeschke, Ullmann's Encyclopedia of Industrial Chemistry, [1]Strain-modulated electron spin resonance spectra of 3d5 ions in ZnSeJ. C. M. Henning, J. H. Den Boef, physica status solidi (b)