bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin magnetic moment and spin resonance of conduction electrons in α‐Sn‐type semiconductors
Authors: Kacman P. , Zawadzki W.
Published: July 2007

The magnetic energy levels in a symmetry‐induced zero‐gap semiconductor of α‐Sn‐type are calculated in the three‐level model. An analytical expression for the g‐factor of conduction electrons is derived and shown to be in good agreement with existing experimental data on HgTe and HgSe. The electron wave function for the conduction band is found explicitly and the optical absorption due to electric dipole transitions between spin states of the same Landau level (electric spin resonance) as well as that due to combined transitions (electric combined resonance) is calculated.
Résonance paramagnétique électronique de l'ion Nd3+ en symétrie cubique dans un monocristal de CaO
Authors: Wasiela A. , D'aubigné Y. Merle
Published: July 2007

L'ion Nd3+ dans l'oxyde de calcium a été étudié par résonance paramagnétique électronique. Le spectre observé est dǔ au quadruplet fondamental Γ8 et l'Hamiltonien de spin correspondant peut ětre caractérisé par deux paramètres P = 0,1085 ± 0,0015; Q = = 2,637 ± 0,0015. On en a déduit les valeurs des paramètres définissant le champ cristallin cubique B4 = −195 × 10−3 cm−1; B6 = −131 × 10−5 cm−1. Les résultats expérimentaux sont comparés à ceux calculés suivant différents modèles de champ cristallin.
Temperature dependence of the bounds on thermal resistance due to U‐process
Authors: Srivastava G. P. , Verma G. S.
Published: July 2007

Temperature dependence of the first two bounds χ and χ on the thermal transport coefficient χ due to three‐phonon umklapp processes is obtained. The results, both in the high‐temperature and low‐temperature approximations, are in agreement with Benin's calculations for solid argon.
On the optical absorption of free polarons at weak coupling
Authors: Devreese J. , Huybrechts W. , Lemmens L.
Published: July 2007

The optical absorption of Frohlieh polarons as a function of the frequency of the incident light is calculated within the Lee‐Low‐Pines formalism. A simple calculation, which is developed here in full detail, gives a result for the absorption coefficient which is exact in order a. Gurevich et al. [1] had obtained this perturbation result using involved calculations based on Green's functions. This result is also extracted here from the “dissipation” calculation of Feynman ct al. [2]. An analytical expression for the optical absorption between 0 < α < 1 is proposed. For α = 1 the main correction to the perturbation result is e decrease of about 15% around the maximum of the absorption. This seems to explain the difference between the experimental absorption detected in CdO (α = 0.75) by Finkenrath et al. [14] and the perturbation result. The effect of a static electric field on the optical absorption coefficient is examined. For low temperatures a shift towards lower frequencies of the threshold for absorptiou is predicted. This shift depends on the mobility and effective mass of the polaron.
Mössbauer effect of Fe57 nuclei in doped A2B4C type semiconductors
Authors: Yarmarkin V. K. , Ikochukhan V. D. , Gricoreva V. S.
Published: July 2007

The Mössbauer spectra of Fe57 nuclei of 1 at% iron impurity atoms are investigated in some compounds of A2B4C type. The isomeric shift and the quadrupole splittings have been determined in the temperature range from −200 to +200 °C. It follows from the comparison with EPR data that in all cases the impurity atoms of Fe have the electron configuration 3d6‐x 4sJ (0 < x, y < 1) and substitute the elements of the I1 group. It has been found that the Mossbauer parameters depend cssentially on the nature of the anion and some cations. An assumption is necessary to compare data on the degree of bond ionicity in the compounds, using Mössbauer parameters.
Electron‐positron colour centre in alkali halides
Authors: Berezis A. A. , Evakestov R. A.
Published: July 2007

The wave function of the F‐colour centre (i.e. the bound state of positron and F‐centre) in alkali halides is determined by a variational calculation in the rigid polarizable point‐ion lattice approximation. The localization of positron on the F‐centre leads to the contraction of the optical electron cloud of the F‐centre. The function of the angular correlation for the two‐quantum annihilation of the positron with the F‐electron is found using the calculated wave function of the F‐centre. It is shown that the trapping model for the positron leads to a better agreement with the experiment than the model previously considered in [5] which describes the annihilation of the F‐electrons with free positrons.
Induced uniaxial magnetic anisotropy in disordered FeAl alloys
Authors: Steinert J.
Published: July 2007

In Fe‐Al alloys the dependence of the induced uniaxial magnetic anisotropy on concentration, direction, temperature, and time was investigated. The results were compared with a theory given by Néel. The part G of the induced anisotropy is caused by A1–Al atom pairs in nearest neighbour position and F is caused by complexes which consist of more than two substitutional atoms. No any contribution of pairs of next nearest neighbours to F were found. In contrast to a theory by Taniguchi the interaction energy of atom pairs with the direction of magnetization shows a linear dependence on temperature. The formation of the induced anisotropy doesn't follow an exponential function on time and therefore it isn't possible to determine their magnitude and activation energy by usual methods.
Analysis of tracer and nuclear magnetic resonance measurements of self‐diffusion in aluminium
Authors: Seeger A. , Wolf D. , Mehrer H.
Published: July 2007

The various nuclear magnetic resonance techniques used for determining self‐diffusion coefficients and activation energies in aluminium are evaluated critically. The data considered most reliable are analyzed together with the Al26‐tracer measurements of self‐diffusion. From the temperature and the pressure dependence of the self‐diffusion coefficients it is deduced that at high temperatures divacancies contribute appreciably to self‐diffusion in aluminium and that the self‐diffusion activation energy for a monovacancy mechanism is Q1  E + E = 1.28 eV. With the help of measurements on the equilibrium concentration of vacant sites Q1 is subdivided into the formation energy E = 0.66 eV and the migration energy E = 0.63 eV. The difference between migration and binding energies of divacancies is found to be E  E = 0.28 eV. It is shown that the ratio of the self‐diffusion activation volume for monovscancies to the atomic volume is smaller than unity and about equal to 0.9.
High‐frequency conductivity of hot carriers in semiconductors with non‐parabolic dispersion law of energy
Authors: Almasov L. A. , Dykman I. M.
Published: July 2007

The tensor of microwave conductivity in semiconductors with isotropic non‐parabolic band in the presence of applied electric field has been calculated. Various frequency ranges of microwave field have been considered. The splitting of plasma frequencies in a constant field has been determined. It is shown that the tensor anisotropy of the dielectrical permeability obtained is manifested in the electro‐optical Kerr effect, observed in [6].
Charge carrier‐exciton interaction in crystalline tetracene
Authors: Peter L. , Vaubel G.
Published: July 2007

Interaction of holes with excitons has been investigated in tetracene crystals at room temperature. It is found that the annihilation of triplet excitons by trapped holes is characterised by a rate constant KT = (1.5 ± 0.5) × 10−10 cm3 s−l. For the rate constant for singlet exciton‐hole annihilation an upper limit of Ks ≤ 1 × 10−7 cm3 s−l is estimated.
Dynamical screening of the wannier exciton
Authors: Zimmermann R.
Published: July 2007

An effective mass equation for the Wannier exciton is derived with a, modified interaction taking dynamical screening due to unbound electron‐hole pairs into account. The binding energies are enhanced which distortes the hydrogenic series formula. In the limit of shallow excitons static screening is justified only in the dominant interaction term whereas the non‐Hermitean splitting terms are substantially affected. The connection with Haken's screening formula with regard to LO‐phonon screening is revealed.
Neutron diffraction by vortex lattlices in superconducting Nb and Nb0.73Ta0.27
Authors: Schelten J. , Ullmaier H. , Schmatz W.
Published: July 2007

Neutron diffraction experiments on flux line lattices in superconducting Nb and NbTa are reported. From experimental data (form factors, lattice parameters, rocking curves etc.) following results are obtained. The microscopic flux distribution of a single flux line in NbTa could be determined. For Nb the form factors are compared with a theory valid in the vicinity of Hc2 A correlation between the flux line lattice and the crystal lattice has been found. Finally the attractive interaction between neighbouring flux lines in Nb has been verified and the resulting maximum lattice parameter compared with the corresponding distance in recent nonlocal calculations.
Statistical perturbation theory of order‐disorder ferroelectrics: First perturbative correction
Authors: Nettleton R. E.
Published: July 2007

The equation‐of‐motion method is used to calculate excitation energies of proton tunneling modes in KD2PO4 using an Ising pseudo‐spin representation of the proton Hamiltonian. The calculation is carried to terms 0 (Z – 〈Z〉) extending an earlier treatment and representing the first perturbative correction in a systematic extension of random‐phase decoupling devised by Wallace. The corrections are small for the deuterated compound, as are the corresponding first‐order contributions to the isotope effect in spontaneous polarization at 0 °K. With increasing temperature, the newly‐calculated terms make a small contribution to the observed decrease in the long‐wavelength excitation energies.
Infrared absorption of SeO and SeO impurity ions in KCl and KBr crystals
Authors: Demyakekko V. P. , Tsyashchenko Yu. P. , Verlan E. M.
Published: July 2007

In the temperature range 120 to 300 °K a study has been made of the infrared absorption spectra of KCl and KBr single crystals doped with SeO and SeO anions. It is shown that the SeO anions in these matrices form complexes SeO · M2+ of symmetry C2V, with cations M2+ (M2+ – Ca2+, Sr2+, Ba2+) similar to the complexes SeO · M2+ and CrO · M2+ observed earlier. A lowering of the local symmetry results in the splitting of V3(F) vibration of the tetrahedral anion SeO. An identification of bands and their fine structure assumed to be isotropic was made in the infrared absorption spectra of the complex SeO · M2+. The existence of similar complexes SeO · M2+ was assumed in KBr and KCI lattices doped with SeO in connection with the quartet structure of infrared absorption spectra in the vibration region V3(E) of the SeO anion.
Paramagnetic resonance and relaxation of Dy3+ and Er3+ in YAsO4 and YVO4
Authors: Schowalter R.
Published: July 2007

Paramagnetic resonance experiments on Dy3+ ions in (Y, Dy)VO4 (100:1) showed both the transition in the ground doublet and the transition in the first excited doublet. The energy gap between both doublets was estimated by comparing the line intensities at various temperatures. By means of a pulse saturation technique at X‐band frequencies paramagnetic relaxation times have been observed in the temperature range of liquid helium as a function of the angle between the optical axis and the magnetic field, and additionally in the case of (Y, Dy)VO4, as a function of crystal size and concentration 100:1, 20:1, and 5:1).
Hyperfine and transferred hyperfine interaction of Cr3+ in yal and lual garnets
Authors: Valentin R. , Luft H. , Baberschke K.
Published: July 2007

The hyperfine field at the 53Cr nucleus and the transferred hyperfine field at the Al3+ neighbours at the next octahedra sites were measured with ENDOR at Cr3+‐doped YAlG and LuAlG single crystals. The electric field gradient at the octahedrally surrounded lattice sites could be determined by the quadrupole interaction with the 27Al nucleus. From the measured quadrupole splitting of 53C13+ a new value of the 53Cr quadrupole moment of |Q| =0.082 b is derived. The magnetic part of the transferred hyperfine interaction between the Cr3+ ion and the A1 nuclei at the next octahedra sites could be well described assuming a point‐dipole model.
The influence of an electric field on the B, n = 1 ground state exciton line of CdS and CdSe single crystals
Authors: Lange H.
Published: July 2007

The influence of an electric field has been measured for the B. n = 1 exciton line of CdS and CdSe single crystals. The results indicate a quadratic Stark shift in agreement with second‐order perturbation theory and a quadratic field dependence of half‐width.
Validity of the electron energy distribution function for piezoelectric scattering at high electric fields
Authors: Sodha M. S. , Phadke U. P. , Chakravarti A. K.
Published: July 2007

A solution of the kinetic equation for the piezoelectric mode of electron‐lattice interaction has been obtained by retaining the higher‐order terms in the orthonormal expansion of the distribution function at high electric fields. It is seen that at low temperatures and moderately high electric fields, the inclusion of the higher‐order terms significantly changes the isotropic part of the distribution function of electrons in piezoelectric semiconductors with low electron densities (for which the analysis is relevant).
Mössbauer study of proton irradiation effects in potassium iron cyanides
Authors: Kisyńska K. , Kopcewicz M. , Kotlicki A.
Published: July 2007

The results of the Mössbauer study of potassium iron cyanides K4[Fe(CN)6] · 3 H2O and K3[Fe(CN)6] irradiated with 1.5 MeV protons are reported. The observed changes in the Mössbauer spectra are interpreted as a result of radiation damage effects and thermal disintegration processes of the compounds. The formation of metallic iron in the superparamagnetic state was observed.
Covalency reduction factors in C4v and D3h and estimation of bonding parameters from magnetic data
Authors: Majumdar D. , Ghosh U. S.
Published: July 2007

The covalency effect in the complexes of the iron group reduces the orbital angular momentum and the spin‐orbit coupling constant from their respective free ion values. Recent interest in penta‐coordinated complexes suggested the derivation of the expressions for the orbital and spin‐orbit coupling reduction factors in complexes of D3h and C4v symmetry. With the help of these expressions and using Slater functions for the radial integrals involved therein the bonding parameters representing the degree of covalency have been estimated from the available magnetic data in the two cases.
Galvanomagnetic effects in many‐valley semiconductors for strong magnetic and heating electric fields
Authors: Mitin V. V.
Published: July 2007

The effect of the heating of electrons on the conductivity of many‐valley semiconductors in strong (but not quantitizing) transverse magnetic fields is studied. It is shown that at low temperatures the current‐voltage characteristic is of S‐type, when the main mechanism of the intervalley scattering of the hot electrons is the emission of inter‐valley phonons. The anisotropy of conductivity is not only reduced but also changes its sign when the electric field grows. The conductivity in strong magnetic fields can be greater than σ0 (σ0 is σ for H ≡ 0, Ex → 0) within a certain region of the electric field strength. All these effects take place as a result of the influence of the Hall field on the heating of electrons and their redistribution with respect to the valleys.
Propriétés magnétiques des composés équiatomiques terres rares rhodium TRh (T  Tb, Dy, Ho, Er)
Authors: Chamard‐Bois R. , Van Nhung Nguyen , Pierre J.
Published: July 2007

Les composés équiatomiques TbRh et DyRh présentent un ordre ferromagnétique, alors que HoRh et ErRh s'ordonnent selon des modes antiferromagnétiques du type (II00). Les moments dans l'état ordonné ont des valeurs réduites en accord avec les résultats d'un calcul de champ cristallin.
Conductivity and hall effect of heavily doped semiconductors at low temperatures in a weak magnetic field
Authors: Van Cong H. , Mesnard G.
Published: July 2007

The transport coefficients of electrons at low temperatures in a weak magnetic field are calculated from a simplified model of heavily doped semiconductors. The treatment is based on the Green function methods, through Feynman path integral formulation, applied to disordered systems and developed already in two previous papers. Two typical cases concerning the relation between the carrier concentration and the donor one are discussed.
An EPR study of an S = 3/2 defect in CaWO4
Authors: Weightman P. , Henderson B. , Dugdale D. E.
Published: July 2007

After n‐irradiation of CaWO4 up to a dose of 3 × 1019 nvt a spectrum consisting of 12 narrow lines is observed. The angular variation of the spectrum shows that a centre with S = 3/2 located at four magnetically inequivalent sites in the structure is involved. The data are consistent with a spin Hamiltonian ℋ︁ = β S · g · B + S · D. · S, where g and D are noncoincident with principal values gz = 2.048, gy = 2.007, gx = 2.004, D1 = 4.32 × 10−4 cm−1, D2 = 0.31 × 10−4 cm−1 and D3 = −4.63 × 10−4 cm−1. Possible intrinsic lattice defects which might account for this spectrum are discussed.
Electron spin resonance and relaxation of tetrahedrally coordinated copper(11) in some complex halides
Authors: Vaughan R. A.
Published: July 2007

Electron spin resonance and relaxation measurements are reported for some copper salts in which the Cu2+ ion has tetrahedral coordination. For the CuCl42− ion in Cs2CuCl4, the results are in some respects at variance with those previously reported [1]. The crystallographic cell parameters for [(C4H9)4N]2CuBr4 have been measured, and in this material a single broad asymmetric ESR line is reported, about 145 G wide at X‐band, having principal g‐values of 2.068, 2.053, and 2.220. Spin‐lattice relaxation times measured by both pulse and continuous saturation methods yielded values of T1 in the range 60 μs at 4.2 K to 140 μs at 1.7 K. These are compared with the much larger values predicted for copper in other tetrahedrally coordinated materials [2]. The ESR spectra of CuCl42− and CuBr42− ion adsorbed on an ion exchange resin are compared with those from powdered samples of the above two complexes. Measurements of T1 for the CuBr42− ion on the resin yielded values of 100 μs at 4.2 K and 280 μs at 1.86 K. It is concluded that the complex halides are not a suitable system in which to study relaxation behaviour of Cu2+ in a tetrahedral crystal field.
Hydrogen in palladium–silver in the neighbourhood of the critical point
Authors: Buck H. , Alefeld G.
Published: July 2007

The chemical potential and the concentration of dissolved hydrogen in Pd0.9Ag0.1have been measured along fifteen isotherms near the critical point. The critical exponent γ, describing the temperature dependence of the lattice gas compressibility, was determined to 1.02 ± 0.04. For the temperature range investigated ((T–Tc)/Tc> 0.01) the isotherms can very well be fitted by Landau's theory. Quantitative arguments are given in favour of the interpretation that the attractive interaction is the long range elastic dipoledipole interaction. From the critical data the dipole strength is found toP= 3.5 eV. The validity of the mean field approximation so close to the critical point is consistent with the assumption of long range interaction.
Energy shift in the resonant absorption of γ‐rays due to disordering of the lattice
Authors: Srivastava B. P. , Sharma H. N. K. , Bhattacharya D. L.
Published: July 2007

A theoretical expression for the energy shift of the resonant absorption of γ‐rays by a disordered lattice has been derived using the double‐time Green's function and taking a simplified model of a vacancy and an interstitial pair in the lattice. Considering only nearest‐neighbour interactions in the harmonic approximation it has been found that in addition to the energy shift due to the second‐order Doppler effect there is an additional shift due to the disordering of the lattice which depends on the position coordinate of the interstitial atoms, the changed force constant of this atom, and the temperature.
Thermal‐electric alignment and stark effect of Z1 centers in KCl
Authors: Jain V. K. , Lüty F.
Published: July 2007

The experimental results of detailed electro‐optical studies on Z1 centers in KCl doped with Ca, Sr, and Ba are reported. For randomly oriented Z1 center systems an isotropic quadratic Stark effect is measured, with a spectral dependence (close to a third derivative of the Z1 absorption) markedly different from that of F centers. The equality of the Z1 center orientations can be disturbed by the application of de fields (about 104 Vcm−1) above 120°K, leading to the development of a linear Stark effect. The spectral dependence and characteristic anisotropy of this linear Stark effect are determined. Quantitative pulse annealing experiments under applied de field show that the Z1 centers reorient with an activation energy of ≈0.4 eV. This process is attributed to jumps of the cation vacancy among equivalent lattice sites within the Z1 complex and will be discussed on the basis of a vacancy‐centered model proposed earlier [1].
On the spectrum of acoustical phonons of a plane‐parallel plate
Authors: Iosilevskii Ya. A.
Published: July 2007

By a method based on the Dyson equation and on the interpretation of boundaries as extended defects in an infinite solid, the phonon Green function of a plane‐parallel elastically isotropic plate of arbitrary thickness is found in a closed analytical form in the acoustical frequency region. The effect of the boundary conditions on the local density of the phonon states is analysed. This effect is found to be spread over a rather considerable distance relaxing mainly as \documentclass{article}\pagestyle{empty}\begin{document}$\frac{c}{{2\omega x}}\sin \left({\frac{{2\omega x}}{c}}\right)$\end{document} where c is the characteristic velocity of sound.
Monte‐Carlo calculations of the blocking effect
Authors: Ryabov V. A.
Published: July 2007

The angular distribution of fast charged particles originating at the lattice sites is studied by computer simulation. Multiple scattering effects were found to be necessary for agreement with the experiment in the planar case. The dependence of the intensity of multiple scattering on crystal thickness and temperature is discussed. Detailed calculations of the blocking pattern are performed for the [100] and [111] directions of a simple lattice (b.c.c.). It is shown that in case of emitting nucleus displacement from the lattice site the most sensitive parameter of the distortion is the value of the originating planar shoulder near a lowindex direction. The distortion of the blocking pattern is calculated as a function of the compound nucleus lifetime.
Absorption spectra of Ti(d2), V(d3), and Cr(d4) ions in CdTe
Authors: Slodowy P. A. , Baranowski J. M.
Published: July 2007

The absorption spectra of divalent impurities Ti(d2), V(d3), and Cr(d4) in cadmium telluride are presented. From the spectra values of the crystal field parameter Δ and Racah parameters B and C are derived and discussed.
Anisotropy of the dielectric constants of trigonal selenium and tellurium between 3 and 30 eV
Authors: Bammes P. , Klucker R. , Koch E. E. , Tuomi T.
Published: July 2007

The reflectivity of Se and Te single crystals has been measured at near normal incidence for photon energies between 3 and 30 eV with the electric field vector lying parallel and perpendicular to the c‐axis of the crystals. The measurements were made using the polarized continuum of the synchrotron radiation of DESY. A Kramers‐Kronig analysis gave the optical constants for both directions of polarization. For both substances electron energy loss measurements are reported. Comparison with optical data gives satisfactory agreement. Even at high energies considerable anisotropic behaviour and several new spectral features are observed. They are discussed in terms of recent band structure calculations.
F‐center hyperfine interactions in LiCl
Authors: Wolbarst A. B.
Published: July 2007

We report an ENDOR study of the F‐center hyperfine interaction constants of LiCl, through shell VIII, at 1.2 °K. The results agree with the previously published values only for the first and second shells.
Conversion and equilibrium between F‐ and F2‐centers in X‐irradiated KCl. I. Slow warm up experiments
Authors: Seager C. H. , Welch D. O. , Royce B. S. H.
Published: July 2007

Measurements are reported in which the number of F2‐centers produced by warming crystals previously X‐irradiated at liquid nitrogen temperatures is studied as a function of temperature and crystal purity. These data are analysed in terms of a diffusion model in which the energy of migration and the initial F+‐center distribution are adjustable parameters. It is shown that the best fit is obtained with an energy of motion of negative ion vacancies (F+‐centers) of 0.66 eV and a vacancy distribution such that the F+‐centres tend to be within five nearest neighbor distances of the F‐centers.
A comparison of the long wave optical phonons in trigonal Se and trigonal Te
Authors: Lucovsky G.
Published: July 2007

The frequencies of the long wave optical phonons in trigonal Se and Te are compared. Differences in the relative frequencies of the A1 and A2 modes, and in several of the elastic constants as well, are attributed to differences in the intra‐ and inter‐chain bonding. These comparisons are made quantitative by defining reduced lattice dynamical properties in which the nearest and second nearest neighbor distances are used as scaling parameters respectively for the intra‐ and inter‐chain properties. The comparison is extended to the optic mode frequencies of amorphous Se and Te.
Electron transport in PdNi alloys with Ni concentration above the critical concentration
Authors: Leger M. G. , Muir W. B.
Published: July 2007

The electrical and thermal resistivities and thermopowers of three palladium‐nickel alloys have been measured between 2 and 77 °K. The alloys had nickel concentrations slightly higher than the critical concentration necessary for low temperature ferromagnetism. The electrical resistivity results indicate that both the electron‐electron and electron‐phonon terms change with composition. The electron‐electron term decreases with increasing nickel concentration and has been attributed to nickel‐nickel interactions which decrease the effective enhancement. The greatly reduced electron‐phonon term in two alloys near 3 at% nickel does not seem to be related to a similar reduction in the coefficient of the T3 term in the specific heat. The thermopower has been observed to change character between 3.1 and 4.3 at% nickel. This effect is similar to previous results on Pd‐Ni alloys which are as yet unexplained.
Dynamique d'un cristal d'urée
Authors: Lefebvre J.
Published: July 2007

La dynamique d'un cristal d'urée est faite dans le cadre de la théorie moléculaire. Un potentiel d'interaction simplifié comportant les potentiels dǔs aux liaisons hydrogène et au moment dipolaire de la molécule permet de calculer l'énergie cristalline (‐27,2 kcal/mol), les constantes élastiques (C11 = 2,37; C33 = 5,12; C44 = 0,648; C66 = 0,058; C12 = ‐1,04 et C13 = 0,79 en 1011 dyn/cm2), les fréquences principales (53; 54; 79; 149 et 219 cm−1), les déplacements quadratiques moyens dǔs à l'agitation thermique et le spectre de fréquences. Ces valeurs théoriques sont ensuite confrontées avec les déterminations expérimentales chaque fois que cela est possible.
Optical bleaching and F → M conversion in doped KCl crystals
Authors: Srinivasan T. M. , Sastry E. V. R.
Published: July 2007

Undoped KCl and KCl crystals doped with Co, Ba, and Cd have been irradiated with X‐rays for various periods and bleached with F‐light at room temperature. The resulting decay of F‐centres and changes in the M‐ and R‐centre concentrations were studied. Co‐ and Ba‐doped crystals X‐irradiated into the second stage of coloration have been found to exhibit, when compared to undoped crystals, (1) greater stability of F‐, M‐, and R‐centres against F‐light bleaching, and (2) higher F → M conversion efficiency. Cd‐doped KCl showed a rapid bleaching of F‐centres without any increase in the M‐centre concentration. The role of impurities in the vacancy and electronic processes which control the bleaching and aggregation of F‐centres is discussed.
High temperature phase transitions and metastability in KDP type crystals
Authors: Grünberg J. , Levin S. , Pelah I. , Gerlich D.
Published: July 2007

Measurements of dielectric constants and infrared reflection were carried out on KH2PO4, KD2PO4, and RbH2PO4 single crystals in the temperature range 300 to 500 °K. Both types of measurements show the existence of two distinct phase transitions Tp and T1 in the above range. The Tp transition is associated with a change in the hydrogen bond. At this temperature the crystal structure changes from tetragonal to monoclinic. The crystal remains in the new structure even after cooling back past the transition to room temperature. Below Tp this phase is metastable and mechanical vibration will release the crystal back to the stable state in room temperature. The T1 transition seems to be dependent on the PO1 and the new phase is also methastable below T1.
Theory of positron trapping by F‐ and F′‐colour centres in alkali halides
Authors: Berezin A. A.
Published: July 2007

The trapping energies of the positron to the F‐ and F′‐colour centres are calculated for NaCl, KCl, and KBr crystals. For the field of F′‐centre the Hultéh potential approximation is used. The values of the positron affinity of the negatively charged F′‐centre are found to lie near 3 eV. This is about twice as much as the positron affinity of the neutral F‐centre which is found to be 1.4 eV for NaCl, 1.6 eV for KCl, and 1.7 eV for KBr.
The influence of optical phonons on the seebeck and Nernst‐Ettingshausen effects in CdTe
Authors: Kubálková S.
Published: July 2007

Detailed measurements are made of the temperature dependence of four transport effects in CdTe: the electric conductivity, the Hall effect, the thermoelectric Seebeck effect (a), and the transversal Nernst‐Ettingshausen effect. (Q). The first two effects have been used for the determination of theoretical values of α and Q. The great discrepancy between experimental and theoretical values of α and Q is explained using Plâvitu's theory of the phonon drag effect of carriers in ionic crystals.
Diffusion of Ni and Ba in MgO up to 2600 °C
Authors: Harding R. C.
Published: July 2007

The diffusion of Ni2+ and Ba2+ in single crystal magnesium oxide has been studied over the temperature range 1100 to 2500 °C using radio isotopes and a sectioning technique. Results indicate that the enthalpies of motion of these two ions in MgO differ by about 10% only. Below about 1500 °C, segregation of impurities to dislocations has a marked effect on the activation energy for diffusion in agreement with the results obtained in cation self‐diffusion studies previously published. The formation enthalpy of a Schottky pair has also been confirmed.
Low temperature X‐ray diffraction and phase transitions in DyVO4, and DyAsO4
Authors: Göbel H. , Will G.
Published: July 2007

Crystallographic phase transitions have been observed in DyVO4, and DyAsO4, at 13.8 and 11.2 °K, respectively by low temperature X‐ray diffraction on powders. These phase transformations coincide with observed anomalies in the temperature dependence of the specific heat. They occur prior to magnetic phase transitions at 3.0 and 2.44 °K, respectively, which were determined by neutron diffraction.
Impurity induced Raman spectra of NaCl and KCl crystals with various monovalent impurities
Authors: Möller W. , Kaiser R.
Published: July 2007

Impurity induced Raman spectra have been measured in NaCl:Br, NaCl:I, KCl:I, NaCl:Li, and KCI:Ag. The strongest scattering intensities are caused by A1g vibrations in NaCl:Br, NaCl:I, KCl:I and by Eg vibrations in NaCl:Li, KCl:Ag. No F2g scattering could be found in NaCl:Li and no A1g, scattering was observed in KCl:Ag. The position and in part the shape of the scattering spectra are discussed. The measured scattering intensities are compared firstly with the polarizabilities (for impurities and neighbours) and the overlap and secondly with the calculated intensities for the three vibration types.
Thermodynamics of strongly anharmonic crystals
Authors: Siklós T. , Aksienov V. L.
Published: July 2007

The properties of the f.c.c. lattice with nearest neighbour central force interaction are investigated in the case of an arbitrary external pressure. The instability temperature, phonon frequencies, phonon widths, and the thermodynamical properties of the f.c.c. lattice are calculated in the high and low temperature limits.
Hahnsches Echo der magnetischen Resonanz im Festkörper
Authors: Fenzke D. , Freude D. , Müller D. , Schmiedel H.
Published: July 2007

Beobachtet man im Festkörper ein Hahnsches Echo, so kann eine Ursache für die Entstehung des Echos die starke magnetische Wechselwirkung der beobachteten Spins mit einer sich außerhalb der Resonanz befindlichen Spinsorte sein. Es wird gezeigt, wie man in diesem Fall Informationen über die geometrische Anordnung der Spins und Korrelationszeiten ihrer Bewegung erhalten kann. An Messungen der Protonenresonanz dekationisierter Zeolithe wird die Effektivität des Verfahrens nachgewiesen.
Diffusion of F‐centers in potassium chloride crystals
Authors: Kuczynski G. C. , Byun J. J.
Published: July 2007

Diffusion coefficients of F‐centers in additively colored KCI single crystals have been measured as a function of F‐center concentration [F] and temperature. It has been found that up to a certain critical concentration which decreases with temperature, these coefficients are independent of [F]. Above this concentration, diffusion coefficients decrease with [F]. Presence of divalent cations seems to increase diffusion rates. Theoretical analysis of the experimental data indicates, that at low [F], diffusion of F‐centers is controlled by electrons hopping from one vacancy to another. At high [F], the dominant transport mechanism is diffusion of cation vacancies.
A Mössbauer study of hyperfine parameters of Sn119 in antiferromagnetic and paramagnetic states of FeSn
Authors: Ligenza S.
Published: July 2007

Mössbauer investigations of Sn119 nuclei in FeSn have been performed at temperatures from 5 to 400 °K. The temperature dependence of the hyperfine field on the tin nuclei on the magnetically ordered (001) planes, of the isomer shift and quadrupole interaction have been studied for two crystallographic sites of Sn nuclei. Different values of the isomer shift and quadrupole parameters were observed in the antiferromagnetic and paramagnetic states of FeSn. It is concluded that in the paramagnetic state the tin atoms on the (001) planes form linear bonds along the c‐axis involving the p, orbitals only, whereas in the antiferromagnetic state the bonds include also the pz and py orbitals which yield the asymmetry of the electric field gradient. On the (002) planes the tin atoms form bonds involving all Px Py Vz orbitals in both the antiferromagnetic and the paramagnetic state of FeSn.
Investigations of the two low lying ground‐level doublets of Dy3+ in YAsO4 by paramagnetic resonance and optical absorption spectrum
Authors: Hillmer W. , Plamper J. , Wappler D.
Published: July 2007

Paramagnetic resonance at K‐, Q‐, and X‐band frequencies and optical absorption spectrum of trivalent dysprosium have been investigated in single crystals of yttrium arsenate within a temperature range from 1.7 to 15 K. The measurements indicate, that there is a linear Zeeman splitting parallel and a nonlinear Zeeman splitting perpendicular to the c‐axis of the crystal for the two lowest ground‐level doublets. The energetic distance of these doublets at zero magnetic field is ΔW = (1.35 ± 0.03) cm−1. A spin Hamiltonian is given with effective spin S = 3/2, which describes the observed Zeeman effect of the two doublets lying close together.
Lattice dynamics and magnetic ordering in the chalcogenide spinels CdCr2S4 and CdCr2Se4
Authors: Brüesch P. , D'ambrogio P.
Published: July 2007

A detailed analysis is presented of the k = 0 phonons of CdCr2S4 and CdCr2Se4 which is based on a simple force model with four adjustable short range parameters. With the help of the derived dynamical matrices for the different symmetry species, the analysis can be performed easily for any compound with the normal spinel structure. From the measured frequencies of the Raman and infrared active phonons of CdCr2S4 and CdCr2Se4 the force constants and eigenvectors of the different normal modes are calculated. We firstly discuss the derived force fields of these two compounds and secondly the coupling between the internal and external lattice vibrations. Finally, with the help of the calculated normal coordinates, the observed influence of the magnetic ordering on the Raman‐ and infrared active phonons of CdCr2S4 and CdCr2Se4 is studied in detail.
The elastic constants of cubic crystals with covalent and partially covalent bonds
Authors: Vukcevich M. R.
Published: July 2007

General formulae for the elastic constants of purely and partially covalent cubic crystals are derived. For the mixed covalent‐ionic bond a new model of electron locale‐transition is proposed, according to which the ionicity of a bond depends on the bonding angle. This model can account, qualitatively, for the elastic properties of ZnS‐compounds. Also discussed are some earlier theories, which appear to be in error, and some broader implications of the proposed model.
Lattice absorption of solid and liquid iodine
Authors: Wagner V.
Published: July 2007

The lattice absorption of I2 single crystals was measured with polarized radiation from 20 to 300 cm−1 at 110 and 300 K. Besides the absorption of the ir‐active phonons there is considerable absorption situated near the inactive internal vibration of the molecule. This absorption is due to two‐phonon processes involving an internal vibrational mode. The corresponding selection rules were deduced. The lattice absorption persists in the liquid phase near the melting point. However, it is altered by strong absorption of the internal vibration.
Influence of the mean free path of the conduction electrons on the magnetic properties of Gd intermetallics ith CsCl structure
Authors: Buschow K. H. J. , Oppelt A. , Dormann E.
Published: July 2007

The variation of Curie temperature with number of conduction electrons in compounds GdAg1 − x, Inx, GdAg1 − x Znx, and GdZn1 − x, Inx is interpreted in terms of the RKKY model. Especially, the influence of a nonconstant exchange integral with a cutoff wavenumber is discussed. The Curie temperatures of compounds with a constant number of conduction electrons were determined for GdCd1 − x Znx and GdAg0.5(1 − x)In0.5(1 − x)Znx. It is shown, that the mean free path of the conduction electrons modifies the strength of the indirect exchange interaction, which can explain, that different Curie temperatures are obtained in compounds with equal number of conduction electrons. The variation of the Pauli susceptibility was estimated from determinations of the magnetic susceptibility of the compounds YAg1 − x Inx YAg1 − xZnx, and LaAg0.5(1 − x)In0.5(1 − xZnx.
ESR study of copper doped NaCl
Authors: Fârcas S. I. , Darabant A. , Nicula A.
Published: July 2007

The ESR spectra of NaCl: Cu systems at LNT and RT are studied. In one of the samples a new paramagnetic centre with [100] tetragonal symmetry was found. The principal values of the g tensor are: g∥ = 2.298 ± 4 × 10−3, g∥ = 2.058 ± 4 × 10−3 In a second type of samples the ESR spectrum of Cu2+ was observed. The g and hyperfine tensors have axial symmetry along a [100] axis. From the parameters of the spin Hamiltonian and from the results of optical spectroscopy the value of the spin‐orbit coupling constant of the copper ion was obtained to λ = (−847 ± 20) cm−l. From this result it is supposed that covalency effects between Cu2+ and the chlorine environment in the NaCl lattice are not important when the crystals are not irradiated.
Energy Transfer between Impurity Molecules of a Crystal in the Presence of Relaxation
Authors: Davydov A. S. , Serikov A. A.
Published: July 2007

The time dependence of the probability W(t) of excitation energy transfer from the donor to the acceptor for various values of resonance interaction energy (ħ L), donor excitation energy relaxation time (γ−1), and the relaxation time (λ−1) of the vibrational part of acceptor excitation energy is found using the method of density matrix. It is shown that W (∞) = \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\lambda \alpha ^2 }}{{(\lambda + \gamma)(1 + \alpha ^2)}}{\rm where } \alpha {\rm = }\frac{{{\rm 2|}L{\rm |}}}{{\sqrt {\gamma \lambda } }} $\end{document}. Thus, W(∞) is proportional to the square of resonance interaction energy at α ⪅ 0.2. However, W(∞) is approximately proportional to α with the values of α satisfying the inequality 0.2 ⪅ α ⪅ 1.7.
Separation of the e1 and E1 Interband Transitions near 2 eV in Germanium by Thermoabsorption
Authors: Kessler F. R. , Dettmer K.
Published: July 2007

By thermoabsorption of Ge thin films (thicknesses 300, 500, and 520 Å, modulation frequency 12.5 Hz, modulation depth δT ≤ 4 K) the interband transitions e1 and E1 in the spectral range near 2 eV are investigated including the transitions with spin–orbit splitting. It is possible to separate these transitions on account of their significantly different temperature dependences: de1/dT = −(5.47±0.02) × 10−4eV/K and dE1/dT = −(3.89±0.02) ×× 10−4 eV/K. The spectral shift divergence overcompensates the Lorentz broadening of the peaks so that their resolubility becomes better at higher mean temperatures. The energies for the transitions extrapolated to 295 K and corrected as to give bulk results are e1 = 2.107 eV, e1 + Δ = 2.294 eV, E1 = 2.134 eV, and E1 + Δ1 = 2.314 eV.
Infrared Absorption in Small Ionic Crystals
Authors: Genzel L. , Martin T. P.
Published: July 2007

The infrared transmission of 0.1 μm crystals of MgO has been measured in the region of fundamental lattice absorption. In particular, the effects of anharmonicity and particle density on the transmission have been observed. These effects have also been calculated using a continuum model applicable to spheres very much smaller than the wavelength of light. In agreement with these calculations, the frequency of the fundamental infrared absorption of small particles was found to decrease with increasing particle density. In addition, it was observed that the frequency dependent damping function of massive MgO must be increased by a factor of about eight in small crystals in order to fit the experimental data.
Lattice Dynamics of MgO Microcrystals
Authors: Genzeland L. , Martin T. P.
Published: July 2007

The eigenvalues and eigenvectors of the modes of vibration of small MgO crystals were calculated using a rigid ion model. The infrared absorption by microcrystals composed of 48 ions was calculated and the infrared transmission of small 0.2 μm cubes was measured. Both the experiment and the calculation exhibit three absorption bands, one weak band at the reststrahl frequency and two more bands at higher frequencies. The calculated density of states of microcrystals composed of 64 and 180 ions is found to resemble closely the density of states obtained using a rigid ion model and cyclic boundary conditions. In addition, the calculated density of states of microcrystals is in good agreement with the measured density of states obtained from inelastic neutron scattering of powder samples.
Pseudopotential Calculation of Binding Energies, Structures, and Lattice Constants of Simple Metals
Authors: Hafner J. , Nowotny H.
Published: July 2007

The nonlocal pseudopotential formalism of Harrison is applied to the problem of binding energies, structures, and lattice constants of nine simple metals. The formulation of the crystal potential is similar to that given by Harrison, but the Kohn‐Sham approximation is used for the description of the core‐valence exchange interaction and the effect of the orthogonalization hole on the core energies is computed by a weighted average scheme. Exchange and correlation between the conduction electrons are taken into account using the modified dielectric function proposed by Kleinman and Langreth. The correct structure is predicted in all cases and the binding energies, equilibrium atomic radii, and axial ratios are obtained with good accuracy.
Optical Anisotropy of β‐Rhombohedral Boron from 0.4 to 16 μm
Authors: Werheit H. , Hausen A. , Binnenbruck H.
Published: July 2007

In the intrinsic range the anisotropy of the reflectivity amounts to about 2% while the dichroism is very small at high photon energies and can only be measured when α ⪅ 2 × × 103cm−1. Especially distinct is the anisotropy of the lattice vibrations. Similar to polycrystalline boron two indirect interband transitions occur; the energy gaps are 1.561 and 1.39 eV with E ∥ c and 1.541 and 1.34 eV with E ⟂ c. The edge tail is dominated by an absorption band, which is possibly caused by C or Si impurities.
On the Localization of Vibrational States in a Disordered Solid
Authors: Böttger H.
Published: July 2007

The localization of vibrational states in an isotopically disordered solid with two types of atoms is investigated in dependence on the average values and the widths of the distribution functions of masses.
Dislocation Jog and Kink Interactions in Ionic Crystals
Authors: Brækrus J. , Lothe J.
Published: July 2007

Jogs and kinks on dislocations in ionic crystals interact both elastically and electrically. In cubic crystals the electrical interaction can be calculated by simple isotropic theory. Anisotropic calculations of the elastic interaction have been performed for a number of ionic crystals of the NaCl type in order to decide whether the net interaction is attractive or repulsive and whether neutral superjogs tend to form.
Intermolecular Triplet Energy Transfer in Naphthalene–Pentacene Mixed Crystals via Higher Excited Triplet States
Authors: Vaubel G. , Peter L.
Published: July 2007

Radiationless intermolecular host‐guest and guest‐host triplet energy transfer involving a hot triplet state of pentacene embedded in a crystalline naphthalene matrix has been observed. The latter process gives rise to delayed fluorescence which increases with the fourth power of the intensity of optical excitation.
Pseudodislocational Interactions in the System Germanium–Arsenic
Authors: Rozhanskii V. N. , Aresenteva I. P. , Zakharov N. D. , Govorkov V. G. , Voinova N. N.
Published: July 2007

The interaction of arsenic pseudodislocations with each other and with dislocations of a germanium lattice is analyzed. The nature of the interaction depends largely on the directed diffusion processes. Interaction between pseudodislocations and gliding dislocations results in a dispersion strengthening of the system.
The Dynamical Behaviour of Silver Chloride with Modified Shell Model
Authors: Singh R. K. , Upadhyaya K. S.
Published: July 2007

A detailed study is presented of the dynamical behaviour of silver chloride using the modified shell model, developed by Verma and Singh, which accounts for the deformation of electron shells introducing three‐body interactions. The results obtained are in fair agreement with the experiments on phonon dispersion. Debye temperatures, second‐order Raman scattering, and infrared absorption spectra of the solid under consideration.