Application of151Eu Mössbauer spectroscopy to studies of electric field gradients in high-temperature superconductors

The rare-earth site of samples having the compositions (Fe,Cu)Sr₂(Eu,Ce) _n Cu₂O_4+2n+z (n=2 and 3) were studied by¹⁵¹Eu Mössbauer spectroscopy. The results obtained are compared with measurements of EuBa₂Cu₃O_7– (123) and Bi₂Sr₂(Ca_1–yEu_y)Cu₂O_8+E (2212) samples. The full quadrupole Hamiltonian of the 21.5-keV -transition was applied in analyzing the measured spectra. Simultaneous fitting of spectra recorded from crystallites oriented in various directions was used to determine the hyperfine parameters of then= 2 and 3 samples. Two different electric field gradients, not discernible in simple random crystallite measurements, were obtained for then=3 series.     

Behavior of copper in gallium arsenide with high tin concentration

Investigations were made of the electrical properties, the cathodolumiescence and photoconductivity spectra, and the temperature dependence of the majority carrier lifetime in gallium arsenide with a high concentration of tin (n=2·10¹⁸ cm^–3, 1.5·10¹⁷ cm^–3) that was doped with copper under different diffusion regimes. Measurements of the Hall effect revealed centers with an ionization energy 0.175 ± 0.005 eV, their concentration depending on the rate of cooling of the samples. The cathodoluminescence and Hall effect data suggest that the cathodoluminescence band observed at 1.35 eV in GaAsSnCu is associated with radiative transitions of electrons to centers with _a =E_v + 0.175 eV. The hole lifetime in GaAsSnCu has a complicated temperature dependence which can be explained qualitatively by the presence of two types of capture center.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 58–63, September, 1980.     

Luminescent properties of A1N activated by europium

The concentration and temperature dependence of emission and excitation spectra was measured on powder A1NEu phosphors. It was shown that A1N: Eu has two luminescent modifications which depend on the activator concentration. At low activator concentration the wide emission band is found in the blue-green region, while at high concentration it is in green region. The excitation spectra of A1NEu consist of wide bands extended from 40×10³ cm^–1 to 22 × × 10³ cm^–1. The emission and excitation spectra are interpreted as transitions between energy levels of Eu²⁺ ions (4f⁷4f⁶ 5d transitions). The structure of the Eu²⁺ luminescent centres and the temperature dependence of luminescence are discussed.The authors thank Dr. M.Polcarová for the RTG measurements and Mrs. I.Míková for the spectral analysis of the A1N: Eu samples. The authors are also grateful to Prof. M.Trlifaj, Dr. J.Pastrák and Dr. J.Kubátová for valuable discussions.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.     

Mössbauer hyperfine interactions in thermally treated iron-yttrium oxide systems

Iron-yttrium mixed oxides in varying ratios (YFe 91, 31, 11, 12, 13, and 19) annealed to different temperatures (850, 1000 and 1250 C) have been investigated by Mössbauer spectroscopy down to 85 K. The Mössbauer spectra are complex in nature, showing up to three magnetically split hyperfine patterns in iron-rich (Y Fe 11, 12, 13 and 19) samples; these three components are attributed to characteristic YFeO₃, Y₃Fe₅O₁₂ and hematite. The yttrium-rich samples (YFe 91, 31) show only one six-line spectrum of YFeO₃.     

Decay of Re186

The decay of Re 186 was investigated with a double focusing spectrometer and scintillation spectrometer. Four transitions were observed with energies of 122·7±0·1 keV, 137·2 keV, 632·2±1·5 keV and 768·2±1·5 keV and the relative-ray intensities 18, 246, 0·9 and 1 respectively. TheK-conversion coefficients determined for low-energy transitions are in good agreement with the theoretical values ( _K ^122·7 =0·53±0·05, _K ^137·2 =0·44±0·02). The relative intensities of theK, L, M andN conversion lines were also determined for these transitions:KL _I +IIL _III M=1·20±0·201·32±0·20 1±0·150·57±0·08 for 122·7 keV transition,KL _I +IIL _III MN=1·57±0·081· 72±0080·70±0·030·20±0·01 for 137·2 keV transition. In the beta spectrum two groups were observed with the end points of 1076±3 keV and 939±3 keV and relative intensities 74±4% and 21±4% respectively. For the branching ofK-capture it was found that 1·5% populates the 122·7 keV level and 3·5% the ground state. The decay scheme from the present results is proposed.The authors would like to thank M. Buriánek and V. Kopiva for help in the measurements.     

Structural relaxation effects on the low-temperature properties of vitreous silica

Measurements of the low-temperature specific heatC and thermal conductivity of vitreous silica after heat treatment at temperaturesT _a between 900°C and 1,400°C are reported. A decrease ofC and an increase of are observed over the whole temperature range studied (C0.06K<T<6K; 0.5 K<T<20 K). Below 1 K the changes inC and (10%) are attributed to a dependence of the density of tunneling states on the fictive temperature. Measurements of the thermal conductivity show that these changes are reversible, thus strongly supporting the evidence for a connection between the tunneling states and the quasi-equilibrium state which is frozen in when an undercooled liquid drops out of thermal equilibrium. Our results are compared to predictions of the free-volume theory of the glass transition. At higher temperaturesC decreases by roughly the same amount as below 1 K while increases by up to 30%. The dependence ofC and onT _a cannot be explained unambigously in terms of a phonon-fraction crossover in the vibrational density of states. Instead, a recently proposed model of coupled SiO₄ rotations is favored.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Light-induced charge transport in BaTiO3 via three charge states of rhodium

By combined studies of electron spin resonance and optical absorption at low temperatures, the charge-transfer bands of Rh⁵⁺ and Rh⁴⁺ are identified to be peaked near 1.6 and 1.9 eV, respectively. On this basis, the light-induced charge-transfer processes in BaTiO₃:Rh are unraveled at room temperature. It is shown that three charge states of Rh are involved, leading to two levels: the shallow Rh^4+/5+ and the deeper Rh^3+/4+ level. The optical behaviour of these two levels corresponds to those expected from a two-center model. The present paper represents the first atomic-scale identification of three charge states of one element leading to optical two-level response.     

Hydroxil and iron ions in YAP: Er laser crystals

⁴S_3/2⁴I_9/2 (1.663m) and⁴I_11/2⁴I_13/2 (2.731m) laser transitions in YAPEr were studied using a material containing Fe, hydroxil impurities and other codopants. Iron impurity causes luminescence quenching of both the⁴S_3/2 and⁴I_11/2 levels whereas OH^– ions enlarge losses, particularly at 2.731m. The effect of iron and hydroxil impurities may be easily diminished by adding Mg²⁺ ions, whereas the admixture of Ce³⁺ or Zr⁴⁺ brings no positive effects.     

FeRu/TiO2 and Fe/TiO2 catalysts after reduction and Fischer-Tropsch synthesis studied by Mössbauer spectroscopy

A series of TiO₂-supported bimetallic FeRu catalysts with different Fe:Ru ratios (; 101; 31; 11; 13) has been studied by means of in situ Mössbauer spectroscopy. The influence of reduction and Fischer-Tropsch synthesis on the state of iron in the FeRu/TiO₂ catalysts will be derived.     

The continuous-spin Ising model,g0∶φ4∶d field theory,and the renormalization group

We have used the method of high-temperature series expansions to investigate the critical point properties of a continuous-spin Ising model and g₀⁴_d Euclidean field theory. We have computed through tenth order the hightemperature series expansions for the magnetization, susceptibility, second derivative of the susceptibility, and the second moment of the spin-spin correlation function on eight different lattices. Our analysis of these series is made using integral and Padé approximants. In three dimensions we find that hyperscaling fails for sufficiently Ising-like systems; the strong coupling limit of g₀⁴₃ depends on how the ultraviolet cutoff is removed. The level contours of the renormalized coupling constant for this model in theg ₀, correlation-length plane exhibit a saddle point. If the ultraviolet cutoff is removed beforeg ₀ , the usual field theory results and the renormalization-group fixed point with hyperscaling is obtained. If the order of these limits is reversed, the Ising model limit where hyperscaling fails and the field theory is trivial is obtained. In four dimensions, we find that hyperscaling fails completely; g₀⁴₄ is trivial for all g₀ when the ultraviolet cutoff is removed.Work supported in part by the U.S. Department of Energy.     

Dynamical chaos in the highly excited states of a quantum Daffing oscillator in an external harmonic field

The energy spectrum of the highly excited states of a quantum Daffing oscillator is considered. It is shown that the energy levels satisfy E_n>E_n+1 and E_n -F²/8², when n , where F² and are the intensity and frequency of the external field. It is suggested that this property of the spectrum is the quantum manifestation of a stochastic attractor in the classical nonlinear limit. This property also takes place for large F².Omsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 90–94, March. 1993.     

Measurement of the reaction γp → K0Σat photon energies up to 2.6 GeV⋆

The reaction p K⁰⁺ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the ⁺ as a function of the kaon production angle in the centre-of-mass system, cos^c.m._K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of p K⁺⁰. The ⁺ is polarized predominantly at cos^c.m._K 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.     

Magnetic and electric hyperfine interactions in the system EuSm

Magnetic and electric hyperfine interactions in the system EuSm were investigated with the isomeric 11/2^– state in¹⁴⁵Eu by applying the time-differential perturbed angular distribution (TDPAD) method. The temperature dependence of paramagnetism was studied between 90 K and 1000 K by measuring the magnetic hyperfine interaction frequency _L=g_NN¹ (T)B_ext. The paramagnetic correction factor strictly follows the Curie-Weiss relation =1+C/(T-), withC=–50(2) K and =–29(5) K. This is compatible with a hyperfine field ofB _int(0)=–25(1) T, a valence of two for Eu in Sm, and antiferromagnetic order at low temperatures.The temperature dependence of the electric quandrupole coupling constant v_Q, investigated between 100 K and 400 K, can be reproduced by a linear temperature variation v_Q(T)=v_Q(0) (1-AT), with v_Q(0)=16.2(4) MHz andA=7.2(8)·10^–4 K^–1.The paramagnetic relaxation time _rel of the nuclear alignment is proportional to the temperature of the sample, with _rel T^–1=3.7(2) ·10^–9s K^–1.This leads to the Korringa relation _J T=const=5.1(5)·10^–11s K for the relaxation time of the 4f electronic spinJ. Assuming that the relaxation ofJ is mainly caused by exchange interaction between conduction electrons and localized 4f electrons at the Eu site, an exchange integral of |J _eff|=0.10(2) eV can be deduced.     

Grassmann-Cartan algebra and Klein-Gordon equations

Given a Riemannian structure (M, g), a hypothesis is investigated that if= _p=0 ⁿ _p (M) is submitted to the differential condition (g++)=0, =mc/—which implies that each component of fulfills the Klein-Gordon equation (- ²) _p =0, ought to be interpreted as a natural complex of the bosonic fields. Then it is found that the complex admits the interpretation in the sense of first quantization with (M) being a convex set of states, with the structure of a Hilbert space over . The definite spin states of bosons are then pure states which are not conserved by the temporal evolution.     

Rare earth doped α-alumina thin films prepared by pulsed laser deposition: structural and optical properties

-Al₂O₃ films doped with about 1% Eu³⁺ were grown on sapphire (012) substrates by pulsed laser deposition using an ArF excimer laser under 10^-4 mbar oxygen pressure and at temperatures higher than 1050 °C. The Eu doping rate was measured by Rutherford backscattering spectroscopy. The crystalline structure was determined by X-ray diffraction and transmission electron microscopy. The films are grown epitaxially on the sapphire substrate. The Eu³⁺ fluorescence spectra are constituted of narrow lines. By means of pulsed laser deposition, Eu³⁺ ions may be introduced into a single site of the -phase lattice, with a concentration that cannot be reached using conventional crystal-growth methods. PACS 81.15.Fg; 68.37.Lp; 78.55.Hx     

Meson decays of hypertritium

Using ³ H and³He wave functions found by multiparameter variation calculations with N-potentials consistent with fundamental hypernuclear data and Afnan-Tang and Malfiet-Tjon type NN-potentials, the fraction of two particle ^–-decays in the total number of ^–-decays in ³ H is calculated and the ³ H lifetime is estimated. The results obtained are compared with experimental data on decay and binding energy of ³ H.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 44–48, March, 1988.     

Detection of3T1?3T2 and3T1?3A2 transitions of Ni by conventional Fourier transform infrared FT-IR spectroscopy

A FT-IR spectroscopic study was carried out in the region 4000–400 cm^–1 for ZnSeNi and ZnSNi at room temperature. The data obtained were examined on the basis of the energy states calculations of the (3d)ⁿ configuration, based on the defect molecule approach. The present investigation reveals the transition from the ground state to the first two excited states namely³T₁–³A₂ and³T₁–³T₂ of Ni⁺² (d⁸).     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Strong probe atom dependence of the electric field gradient in Bismuth

The nuclear quadrupole interaction of the 8⁺ isomers in^{206, 208}Po was measured in the semimetallic host Bi. The comparison of the extracted electric field gradient eq for PoBi with the values for the neighboring elements Bi and Pb as probe atoms in Bi reveals a very drastic increase from Pb to Bi and to Po by an order of magnitude: eq_PbBi eq_BiBi eq_PoBi =1.64(10)4.8(3)16(2)(all values at room temperature in units of 10¹⁷ V/cm²). This behavior is discussed in terms of the changing number of outerp-electrons of the probe atoms.