The electrical properties of manganese-copper ferrites

The electrical resistivity and the Seebeck coefficient were measured in the temperature range 80–800 °K on single crystals and polycrystals from the system of manganese-copper ferrites Cu_0.5Mn_zFe_2.5–zO₄(0 z<1). While the temperature dependence of of single crystals and polycrystals were different, the temperature dependences of both single crystals and polycrystals displayed the same course and indicated n-type electrical conductivity. The dependence of the electrical properties on the chemical composition showed three regions: in the two first regions (for 0z<0.3 and 0.3<z<0.7) a conduction mechanism predominates which is characteristic for the coexistence of Fe²⁺ and Fe³⁺ in octahedral sites of the spinel lattice; in the third region (forz > 0.7) a new conduction mechanism plays a significant role which is probably due to the presence of the copper ions in those ferrites.The authors are greatly indebted to Dr. S. Krupi~ka for constant encouragement and valuable discussions, to Mr. E. Kitzinger and Mr. M. Vichr for the preparation of the polycrystal and single-crystal samples respectively and to Mr. A. Novfik for the careful chemical analysis.     

Synthesis,growth and characterization of L-proline dimercuricchloride single crystals for frequency conversion applications

A semi-organic nonlinear optical L-proline dimercuricchloride (LPDMC) material has been synthesized. LPDMC single crystals were grown from aqueous solution by a slow cooling method. Good quality single crystals of size 19×6×3 mm³ have been grown over a period of 3 weeks. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the cell parameters. The title compound crystallizes in the triclinic system with a noncentrosymmetric space group P1 and with unit-cell parameters a=7.2742(4) Å, b=9.4472(5) Å, c=10.4767(6) Å, α=108.621(3)^°, β=107.260(2)^°, γ=97.353(2)^° and volume=631.51(6) Å³. Optical and dielectric properties of the crystals have been studied. The thermal stability of the crystals was determined by thermogravimetric analysis/differential thermal analysis. The second harmonic generation efficiency of the crystals was obtained by the classical powder technique using a Nd:YAG laser and it is found to be 2.5 times that of potassium dihydrogen phosphate.     

Optical and magneto-optical studies of a multiferroic GaFeO<Subscript>3</Subscript> with a high Curie temperature

Single crystals of a noncentrosymmetric orthorhombic pyroelectric ferrimagnet Ga_2?xFe_xO₃ with a Curie temperature within 260–345 K have been grown by the flux method. It has been found that the electrical properties of the single crystals varied over a broad range from 10⁵ to 10¹³ Ω cm depending on the presence of transitionmetal oxide impurities. The dispersion relations for all three principal dielectric functions of orthorhombic GaFeO₃ have been determined in the range 0.7–5.4 eV by spectroscopic ellipsometry. The spectra of the dielectric functions of the orthorhombic Ga_2?xFe_xO₃ crystals are compared with the spectra of the trigonal crystals. The Faraday effect and second-harmonic generation are studied, and the law of the transition to the paramagnetic state has been determined. The crystallographic and magnetic contributions to the second-harmonic generation are analyzed.     

New determination of quadrupole coupling constants of Li isotopes in single crystals LiIO3 andLiNbO3

Quadrupole effects in NMR spectra of⁸Li(I =2⁺;T _1/2=0.84 s) in LiIO₃ andLiNbO₃ single crystals have been detected by use of a modified -NMR. The coupling constants for both crystals are in agreement with known ones. Field gradients in the crystals were measured by detecting pulsed-Fourier transformed NMR of⁷Li. The quadrupole moments deduced from both samples agree, and|Q(⁸Li; 2⁺)|=32.7±0.6 mb has been determined.     

The effect of the time of flight of neutrons on the decay constant measurements by the pulse method

The effect of the time of flight of neutrons escaping from the moderator on the measured time dependence of the neutron density, which in turn serves for determining the decay constant , has been analyzed. The measured values of a have been found to vary considerably with the distance of the detector from the moderator and also with its size described by the bucklingB ². Measurement with light water and loose diphenyl has shown that the deviation in depends also on the type of moderator.The authors would like to thank Mr. J. Jirou and Mr. J. Jadavan for their collaboration in the measurements and for maintaining the electronic apparatus and the accelerator as well. The authors also acknowledge the help of Dr. M. Nepraová in preparing the computer programme.     

Electronic properties of single-crystal diamonds heavily doped with boron

Single-crystal diamonds with characteristic sizes of 2–7 mm doped with boron in the concentration range 10¹⁹–10²⁰ cm^?3 have been grown by the temperature gradient method at high static pressures. The temperature dependence of the resistance R of the synthesized single crystals has been measured in the range 0.5 K < T < 297 K. An activated dependence R(T) with an activation energy of about 50 meV is observed in the range from room temperature to T ≈ 200 K. At temperatures below approximately 50 K, the temperature dependence of the conductivity for heavily doped crystals is proportional to T ^1/2, which is characteristic of degenerate semiconductors with a high number of defects.     

The decay of110mAg to110Cd

The gamma-ray spectrum of the decay of^110mAg has been measured with the Ge(Li) detectors. A total of 32 gamma rays associated with the decay of^110mAg have been observed and their intensities determined. A number of gamma-ray transitions have not been observed previously. The K-electron internal conversion coefficients were found from the relative gamma intensities used in conjunction with published K-conversion electron intensities.It is proposed that the level scheme of¹¹⁰Cd has new levels at 1410·4, 1443·2 and 2237·7 keV in addition to the previously known levels. The spins and parities of the new levels are discussed.The author wishes to express her gratitude to Professor V. Petrílka for his permanent support and to Mr. J. Lipták and Mr. J. Vrzal for valuable assistance and discussions.     

Heat-stimulated currents in semi-insulating gallium arsenide

The energy spectrum of charge carrier traps of semi-insulating n-type gallium arsenide has been investigated by the method of heat-stimulated currents and the parameters characterizing these traps have been estimated. Trap acceptor levels with energies 0.37, 0.41 and 0.17, 0.28, 0.32, 0.34, 0.38, 0.40 eV have been found for samples with the specific resistivity 2.7 · 10⁷ and 1.6 · 10⁸ · cm, respectively. The results obtained are well explained within the framework of the theory of a compensated semiconductor.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 22–26, November, 1971.The authors are grateful to A. P. Vyatkin, V. G. Voevodin, and E. V. Kozeev for kindly providing the gallium arsenide crystals and stimulating the research.     

The Β decay of the new isotope79Y

The neutron deficient isotope⁷⁹Y has been firstly identified and the decay properties were studied from-decay measurements in the reaction of⁵⁴Fe(²⁸Si,p2n at 92 MeV. Three rays of 152.5, 177.4, and 1106 keV were observed concerning the decay. The half life and Q_EC value were determined to be 14.9 ± 0.6 s and 7.12 ± 0.45 MeV, respectively. The decay scheme including spin-parity is discussed, and 5/2⁺ assignment for the ground state is proposed.We would like to thank to Dr. Y. Maeda for his valuable advice about the electroplating method of iron targets. We also thank to Mr. T. Maeda and Mr. S. Niiya for preparation of hardware for data-taking.     

Experimental study of ternary fission of U235 with thermal and resonance neutrons

The alpha particle spectra from ternary fission of U²³⁵ have been investigated in the thermal and the resonance neutron energy regions. The resonance neutrons have been obtained by passing the reactor neutron flux through a boron filter. A silicon surface barrier detector telescope technique for alpha particle detection has been used. In the resonance neutron energy region the ratio _f / _f has been found to be 1·02 ± 0·2 times the value of _f / _f in the thermal region. The non-gaussian tail of the LRA energy distribution has been observed.The authors are indebted to Dr. I.Wilhelm, Mrs. M.Pospíilová, Mr. J.vanda for their kindly help in the experimental data handling and to Mr. V.Kvítek for his assistance during the experiment.     

Radiation and thermally induced effects in YAlO3:Mn crystals

We have studied effects induced by γ-radiation and temperature in Mn-doped YAlO₃ crystals. The studies have been performed by means of optical spectroscopy that include measuring of optical absorption changes induced by γ-radiation and elevated temperature as well as thermally stimulated luminescence (TSL). It has been shown that under γ-irradiation of YAlO₃:Mn crystals, along with the ionization of Mn_Al⁴⁺ ions (Mn_Al⁴⁺→Mn_Al⁵⁺+e⁻), some additional coloration processes take place. This additional coloration is characterized by a wide intense band centered at 26,000- that is ascribed to color centers intrinsic to YAlO₃ lattice. This coloration is removed by the way of crystal warming at , while the coloration caused by Mn_Al⁵⁺ ions is removed at higher temperature . The observed TSL glow of irradiated crystals reveals three peaks near 360, 400 and that correspond to three types of traps. Parameters of the traps have been determined. The TSL emission corresponds to intra-center luminescence of Mn_Al⁴⁺ and Mn_Y²⁺ ions. The possible ionization and trapping mechanisms in YAlO₃:Mn crystals are discussed.     

Mössbauer study of119Sn defects in silicon from ion implantations of radioactive119In

Radioactive¹¹⁹In⁺ ions (T _1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV -radiation of the daughter¹¹⁹Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.     

Optical and Paramagnetic Properties of Synthetic Diamond Single Crystals with a Low Content of Nitrogen

Optical and paramagnetic properties of synthetic diamond single crystals grown by the temperature gradient method in the Fe-Co-C and Fe-Co-Al-C systems using split-sphere high-pressure apparatus have been investigated. For crystals with a high (>5·10¹⁷ cm^–3) nitrogen concentration a good agreement of the concentrations of single substitution nitrogen atoms obtained from EPR, IR, and UV measurements was observed. For crystals with a low ((0.5–5.0)·10¹⁷ cm^–3) nitrogen concentration, there was no correlation between the results of substituting nitrogen concentrations obtained by the methods mentioned. It is shown that this behavior is attributable to the transition of the substituting nitrogen atoms from the paramagnetic neutral to nonparamagnetic positive charge state due to compensation by the boron impurity.     

Crystal-Physical Model of Ion Transport in Nonlinear Optical Crystals of KTiOPO<Subscript>4</Subscript>

The ionic conductivity along the principal axes a, b, and c of the unit cell of the nonlinear-optical high-resistance KTiOPO₄ single crystals (rhombic syngony, space group Pna2₁), which are as-grown and after thermal annealing in vacuum, has been investigated by the method of impedance spectroscopy. The crystals were grown from a solution-melt by the Czochralski method. The as-grown KTiOPO₄ crystals possess a quasi-one-dimensional conductivity along the crystallographic c axis, which is caused by the migration of K⁺ cations: σ_║c = 1.0 × 10^–5 S/cm at 573 K. Wherein the characteristics of the anisotropy of ionic conductivity of the crystals is equal to σ_║c/σ_║a= 3 and σ_║c/σ_║b= 24. The thermal annealing at 1000 K for 10 h in vacuum increases the magnitude of σ_║c of KTiOPO₄ by a factor of 28 and leads to an increase in the ratio σ_║c/σ_║b= 2.1 × 10³ at 573 K. A crystal-physical model of ionic transport in KTiOPO₄ crystals has been proposed.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Synthesis and properties of single crystals of nickel zinc ferrite

A method for growing single crystals of nickel zinc ferrite using PbO-PbF₂ as a flux under a gas pressure of 15 atmospheres of argon mixture is described.The magnetic properties indicate that with the addition of zinc oxideK ₁/M decreases in absolute value. TheH increases with zinc content. Theg value decreases and reaches 2·05 forx=0·8.The author wishes to thank Dr. Braginski and Dr. Krishnan for friendly cooperation and for valuable discussion, Mr. Duclos and Mrs. Enaud for performing the chemical analysis and Mr. Sanz for technical assistance in preparing the single crystals.     

The influence of quenching rate on the kinetics of transformations of metastable phases in the Al-30 wt.% Zn alloy

The effect of quenching rate on the precipitation process in the Al-30 wt. % Zn alloy has been studied by the X-ray diffraction and electron microscopy. No effect has been observed both on the T-T-T curve for the transformation of coherent into semicoherent phase and on the isothermal growth of precipitates of these phases. The significant dependence has been, however, found when the ageing of the investigated alloy led to the formation of incoherent phases. The T-T-T curves for _R and _R transformations are shifted to the shorter ageing times with the increased quenching rate. The slopes of these T-T-T curves yielding parallel straight lines remain unchanged. The role of coherency stresses and of quenched-in strains in the investigated processes is discussed.In conclusion the authors would like to express their appreciation to Doc. Dr. V.Syneek, CSc. for his valuable discussions and to Ing. V.íma for the preparation of Al-Zn alloys. Our thanks are also due to Mr. V.Petr and Mr. Z.iký for their help in the heat-treatment and X-ray diffraction measurements of the investigated samples, and to Mr. P.Vyhlídka for the homogeneity control of the Al-Zn alloys.     

Elastic strain and coloration pattern in natural quartz crystals

Very small elastic strains (tilts of the order of 0.25 sec of arc and dilationsΔd/d?10^?6, whered is the spacing of net planes) have been observed in natural quartz crystals. According to their rocking curves which are of almost theoretical width, these crystals were commonly expected to be practically perfect crystals. On double crystal X-ray topographs a pattern was revealed of uniformly strained layers parallel to the rhombohedron faces (10¯11) and with thickness ranging between 20 and 200 microns. This fine structure strain pattern was correlated to the pattern of the optical coloration which could be produced by irradiating the originally transparent crystals with X-rays. A localincrease of coloration matched with a localcontraction of the lattice. Tilts occurred in transition zones between adjacent layers with slightly different lattice spacings. Strain and coloration patterns probably have as a common cause the deposition of layers with different impurity concentrations during the growth process of the crystals. Although no change of the strain as a result of the X irradiation could be detected in the colored layers in particular, experimental evidence has been found for anoverall expansion of the lattice of the order ofΔd/d?5×10^?7 due to X irradiation. This expansion seems to saturate at this low value and is probably caused by electronic processes connected with the coloration. Some aspects concerning the nature of the color centers have been discussed. It seems likely from the results of the strain measurements that both sets of layers, colored and transparent ones, play a combined role in coloration.     

Search for the lowest 2+ mixed-symmetry state in102Ru

TheK-conversion coefficients of some 2_i ⁺ 2_f ⁺ transitions in¹⁰²Ru have been measured and their electric monopole components have been deduced. The intensity of theE0 component in the 2₃ ⁺ 2₁ ⁺ transition supports a possible interpretation, based on gamma decay, of the 2₃ ⁺ level as the lowest mixed-symmetry state. Negative parity has been assigned to the level at 2261 keV.We would like to thank Mr. M. Ottanelli for his continuous, important technical support. One of the authors (D.C.) thanks the INFN for hospitality and financial support during this work.