Slow paramagnetic relaxation versus magnetic ordering of high-spin iron III in trigonal bipyramidal environments: Hyperfine splitting of the low temperature Mössbauer spectra of some high symmetry chloroferrate anion salts, [FeCl 5 2− ] and [FeCl5(CH3OH)2−]

A combination of Iron-57 Mössbauer spectroscopy and magnetic susceptibility measurements are used to show that the [FeCl₅ ^2–] and [FeCl₅-(CH₃OH)^–2] anions (stabilized in the solid state by large quaternary cations) undergo ferromagnetic order, T_critical6 K.     

Smooth phase in the one-dimensional discrete Gaussian model with 1/(−j)2 interaction at inverse temperature β>1

We consider the one-dimensional discrete Gaussian model with interaction energyg satisfyingg(i, j)=g(i–j)1/(i– j)² and prove that for the inverse temperature>1 this system displays a smooth phase characterized by <(n _{n 0} –n _{y 0})²> C < if the nearest neighbor coupling g(1) is sufficiently large. Our method also allows us to treat the 1/(i– j)² Ising model and reproves the existence of spontaneous magnetization under the above conditions.     

Anion dependence of the valence state detrapping behavior for a fused hydrocarbon bridged binuclear mixed valence iron compound and its di-oxygen sensitivity

Monocationic forms of the symmetric and asymmetric indacene bridged species [(Cp^*Fe)₂(-s-indacene)],I, and [(Cp^*Fe)₂(-as-indacene)],II, are fully detrapped and trapped, respectively, over the entire range from 1.5 K to ambient temperature as their BF ₄ ^– salts. In contrast to [II ⁺][BF ₄ ^– ], the TCNE^.– salt [II ⁺][TCNE^.–] exhibits a transition from fully trapped to a largely detrapped valence state behaviour over the increasing temperature range 100 to 300 K. Mössbauer spectra ofI suggest that while it is relatively insensitive to oxygen as a neat solid, it is strongly oxidized by O₂ in dry hexane solution. Similar studies ofII indicate essential insensitivity to O₂, both as a solid and in hexane solution.     

Microplasticity of silicon crystals

The low-frequency (1 Hz) internal friction (Q^–1) method was used to study the microplasticity of silicon whisker crystals grown by the method of chemical gas-transport reactions in a closed ampoule. A study was made of p-type crystals with the growth axis 111, 1–60 in diameter, working length 1–3 mm, both in the original state and after plastic ( 1%) deformtion by torsion. The temperature and amplitude dependences of Q^–1 were studied in 5·10^–5 torr vacuum. The amplitude of alternating vibrations was within the range 10^–5–10^–3 and the axial stresses were 10⁶–10⁷ N/m². The experimental results led to the conclusion that the microplasticity of undeformed silicon whiskers was due to heterogeneous nucleation of dislocations in stress concentration regions near surface defects, assisted by thermal fluctuations. In deformed whiskers the microplasticity was attributed to the nucleation and motion along dislocations of single and double thermal kinks in accordance with the Seeger model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88–93, May, 1980.     

A repetitively pulsed sealed-TE CO2 laser using an oxygen tolerant discharge scheme

A repetitively pulsed (40 Hz) TE CO₂ laser using an oxygen tolerant discharge scheme is described. Long lived (>10⁵ shots) stable discharges at high pump energy density (200 J.l^–1 atm^–1) have been achieved both with and without the use of additive gases.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Laser-induced fluorescence detection of singlet CH2 in low-pressure methane/oxygen flames

Methylene, CH₂, is a chemically important intermediate in hydrocarbon combustion but has previously eluded optical detection in a combustion environment. The CH₂ signal as a function of height above the burner surface in a premixed, laminar, methane/oxygen flame (5.6 Torr and fuel equivalence ratio 1.05) is measured by laser-induced fluorescence (LIF) in the B ₁ – ã¹ A ₁ electronic system. The ã state which lies 3165 cm^–1 above the ground state is populated at the high temperatures of the flame (800–1800 K). Although less than one photon for each laser pulse is detected, we can unambiguously attribute the LIF features in the region 450 to 650 nm to CH₂ by both scanning the excitation laser and dispersing fluorescence. LIF temperatures and CH and OH LIF concentration profiles are also obtained for the flame. The CH₂ radical concentration maximum occurs closer to the burner than that of either OH or CH, as expected from models of methane combustion chemistry.     

Ferromagnetic resonance and magnetic crystallographic anisotropy of monocrystalline lithium ferrite films

The crystallographic anisotropy constant K₁ of monociystalline lithium ferrite films was measured by the methods of ferromagnetic resonance and rotational moments. The presence of uniaxial anisotropy in the plane of a film with the constant K_u 10₃ erg · cm^–3 is established experimentally. The nature of the uniaxial anisotropy is explained by the anisotropy of the stresses in the plane of the film, a formula is obtained to compute the angle of deflection of the easy magnetization axis from the crystallographic direction. An estimate is made of the difference in the stresses along the axes (_x–_z) 10¹⁰ dyne · cm^–2.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 86–89, September, 1973.     

Quasistatic magnetic permeability of an amorphous ferromagnet

Dependence of the differential magnetic permeability on the speed of magnetization reversal was found in ribbons of an amorphous ferromagnetic material. When the ribbon thickness is 10^–3 cm and the initial permeability is 10^–5, an increase in the frequency of the harmonic magnetization reversal causes a decrease of by a factor of 2–3; this takes place in the region around 100 Hz. The effect is explained by the influence of eddy currents on the magnetization distribution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 58–62, January, 1986.     

New far-infrared laser lines produced by resonant Q-branch-pumping of CH3F

Conclusion We showed that by pumping the ₃-Q-branch of CH₃F using the 9P-branch radiation produced by a continuously tunable 20 atmospheres CO₂ laser all Q-branch transitions with quantum number 5J28 can be pumped. From the 23 laser lines with frequencies from 10 cm^–1 to 47 cm^–1, 13 were detected for the first time. The optimum operating pressure for the FIR laser was 11 Torr.     

The behavior of copper impurity in CdSnAs2

Single crystals of n-type CdSnAs₂ with a carrier concentration of 2 ·10¹⁷–4 ·10¹⁸ cm^–3 and mobility (3 to 6) · 10³ cm²/V ·sec were copper doped by diffusion saturation at temperatures from 400 to 570C. As a result of the study of the electrical properties of the doped crystals it was established that the copper in CdSnAs₂ is a fast-diffusing acceptor impurity. The solubility of Cu depends primarily on the donor-center concentration and has clearly a retrograde character. Low-temperature heat treatment (over the 200–400C range) of the Cu-doped specimens results in an increase in the acceptor concentration. The form of the log R(10³/T) curve indicates the existence of acceptor centers with an ionization energy of 0.05 eV in the Cu-doped CdSnAs₂ specimens.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 39–44, July, 1973.     

Spatial shape and development dynamics of auroral scintillation patches

Results of simultaneous measurements of altitude distribution of auroral small-scale irregularities and total electron content by the method of radio illumination of the ionosphere by signals from an orbital satellite at 150–400 MHz are presented. It is shown that under magnetically quiet conditions the small-scale irregularities (1km) tend to occupy local regions, which extend over 100– 200 km along the geomagnetic fieldB with 5– 20 km from the North to South. Characteristic times of formation and collapse of such local structures under the conditions of weak geomagnetic activity are of the order of more than one hour.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 3, pp. 276–285, March, 1996.This work was supported by the Russian Foundation for Fundamental Research (grants Nos. 93-02-3360 and 96-02-18500-a.)     

Laser separation of oxygen isotopes by IR multiphoton dissociation of (CH3)2O

Isotopically selective (with respect to ¹⁸O) one- and two-frequency multiphoton dissociation of dimethyl ether (CH₃)₂O by pulsed TEA CO₂ laser radiation has been studied. The maximum primary selectivity, 16, is attained with the dissociation yields of the desired component (CH₃) ₂ ¹⁸ O ₁₈=5×10^–4 and 1.7×10^–2 for one- and two-frequency excitation, respectively. The dependences of MPD yields and selectivity on laser radiation frequency, (CH₃)₂O pressure, buffer gas (N₂) pressure and temperature have been measured. Multiphoton absorption coefficients have been measured and the average number of absorbed quanta calculated. The laser photon energy consumed for separating one ¹⁸O atom has been estimated: 11 and 4 keV/¹⁸O atom for one- and two-frequency excitation, respectively.     

Neutralizing a high-aperture metal-ion beam

It is found that secondary electrons ejected by the ions from the collector are responsible for neutralizing 300 sec pulses of wide-aperture ion beams (about 100–300 cm²) formed by various metals and having current densities ji of about 10^–2 A/cm² and energy _i 100 keV. A negative potential _ee=–500 V applied to the extracting electrode relative to the grounded collector improves substantially not only the beam neutralization in the transport section but also the ion generation efficiency in the accelerating gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 53–56, April, 1990.     

A pulsed laser employing Ar+ ions at high currents and low pressures

There are several papers [1–5] on pulsed Ar⁺ lasers, but all the tests have been done at low current densities (100 A/cm²). We have used densities up to 15–20 kA/cm², the best pressure range being 8×10^–3 to 2×10^–2 mm Hg. The generation under these conditions has some features not seen under ordinary conditions.     

Transient absorption and laser output of YAG : Nd

YAG : Nd grown under 98% Ar 2% H₂ protective atmosphere free of nitrogen or hydrocarbons showed after UV irradiation broad absorption peaked at 1·9×10⁴ cm^–1 which disappeared relatively slowly at room temperature. It was more intensive in oxygen treated samples than in those annealed in hydrogsn. Transient absorption suppresses laser output by the increase of absorption at 0·94×10⁴ cm^–1 (1064 nm) and, particularly in CW mode, by the anomalous rod deformation. YAG : Nd containing Fe ions (2·10^–4 wt%) showed no transient absorption.     

Correlations between frequency of infra-red active vibrational modes and copper-oxygen distance in copper oxides. Application to superconductors

The infra-red spectra of a large number of ternary Cu(II) oxides with at least a quasi square-planar coordination of oxygen around the copper ions have been studied. The frequency of the bands with the highest frequency,v _max, is found to correlate extremely well with the shortest Cu–O distance.v _max increases at an impressive rate of 20 cm^–1 per 0.01 Å when the Cu–O distance becomes less than 1.97 Å, which is the Cu²⁺–O^2– distance in square-planar CuO₄ complexes as obtained from empirical ionic radii considerations. The marked sensitivity may be used as a titration procedure not only to assign bands but also to obtain diagnostic information about local coordination in compounds derived, for example, from the YBa₂Cu₃O_7–d structure such as LaCaBaCu₃O_7–d . The only example where this correlation fails is in the two-layer non-superconducting oxides derived from La₂(Ca, Sr)Cu₂O₆. The significance of this result is discussed. The marked dependence of frequency on the bond-distance is qualitatively examined in terms of an increased electron-phonon coupling to account for the observed tendency of the superconducting transition temperature to go through a maximum as the average basal plane Cu–O distance is decreased.     

Thermodynamics and phase stabilities of the ternary system Li-In-Sb

Electrochemical investigations of the phase equilibria of the ternary system Li-In-Sb show the existence of two new ternary phases, Li₃InSb₂ and nominally Li₆InSb₃ which has a wide range of stoichiometry along the quasi-binary cut InSb-Li₃Sb. Both compounds are stable in equilibrium with elemental indium and antimony. The lithium activities are limited to ranges from 6.6×10^–8 to 3.6×10^–7 and 9.3×10^–8 to 1.1 ×10^–5, respectively, at 400 °C. The standard Gibbs energies of formation of Li₃InSb₂ and Li₆InSb₃ are –296.2 and –568.8 kJ/mol, respectively, at 400 °C and ideal stoichiometry. The activity ranges of Li, In and Sb are given for the stability of all phases of the ternary system.On leave from Institut für Physikalische und Theoretische Chemie, Technische Universität Graz, Austria