High-pressure phases in the GaSb-Mn system

The effect of high pressure (6 GPa) on the formation of new phases in a polycrystalline mixture GaSb: Mn = 1: 1 upon heating was studied. Sphalerite-type solid solutions with a small amount of Mn form at temperatures below 520–600 K. At higher temperatures, new crystalline GaSbMn phases are synthesized: a phase with a simple cubic structure with a lattice parameter a = 2.946 ± 0.001 Å (at 620–670 K) and a phase with a tetragonal CuAl₂-type structure (space group I4/mcm) with lattice parameters a = 6.426 ± 0.004 Å and c = 5.349 ± 0.004 Å (at 690–870 K). These new phases are metastable under normal conditions and have magnetic properties. The structure, conductivity, and thermal stability of the synthesized phases are investigated, and the products of decomposition of these new phases upon annealing are analyzed.     

New phases in the most basic zone of the system Ba−Cu−O

Summary In the most basic part of the binary system BaO−CuO two new compounds were identified corresponding to the Ba₂CuO₃ and Ba₃CuO₄ formulae. Another more oxidized phase of composition Ba₂CuO_3+δ was also obtained, which can exist in two crystalline modifications. For all these new substances the structural type and the lattice parameters are reported.     

Characterization of phases in the Fe-Nb system

The Fe-Nb system was investigated by means of X-ray diffraction and Mössbauer spectroscopy (at 300 and 77 K), in the range from 1 to 66.7 at%. We have found that the limit of solubility of Fe in Nb at 1100°C is between 3 and 4 at% Fe, and observed the coexistence of the Nb solid solution (Nbss) phase and Fe₂₁Nb₁₉ in the range from 4 to 40 at% Fe. The Mössbauer parameters of all the single phases are reported. The lattice parameters of Nbss phase present no significant variation with the Nb content. The X-ray pattern for the Fe₂₁Nb₁₉ phase could not be solved. The Laves phase Fe₂Nb presents Mössbauer and X-ray parameters that agree with the literature.     

Spin-spin correlations in the insulating and metallic phases of the Mott system V 2 O 3

The magnetic response in V ₂ O ₃ has been investigated using polarised neutron scattering with polarisation analysis. Measurements were carried out at three temperatures corresponding to the antiferromagnetic insulating ground state, the metallic phase and the high temperature metallic phase. At the first order metal insulator transition there is a dramatic change in the magnetic response with the metallic and high temperature metallic phases being characterised by ferromagnetic spatial correlations of the paramagnetic response. The establishment of ferromagnetic correlations at the metal insulator transition accounts for the abrupt jump in the uniform susceptibility. It is proposed that the differentiation of the V-V distances across the edges of VO ₆ octahedra is of critical importance for the change in electronic conductivity but also for the establishment of the spatial correlations. The gradual high temperature evolution of the conductivity then occurs by the reduction in the vanadium d overlap brought about by thermal expansion. The first order reduction in atomic volume which occurs on the establishment of the metallic phase results from an instability of the vanadium local moment arising from the change in electronic structure. Received 7 April 1999     

New metastable phases of silicon

It has been known since 1963 that a metastable phase (III,BC-8) results from the decompression of silicon from its high pressure metallic phases. However recent theoretical studies suggest the possibility of several metastable phases with similar total energies. Upon rapid release of pressure from the metallic state, two new, metastable, phases of Si have been discovered, with tetragonal structures. X-ray diffraction data on these new phases are presented.     

Orientational bonding of phases accompanying directed crystallization of the eutectic of the system Si-TiSi2

The characteristic features of structure formation in cast and direct crystallized alloys of the system Si-TiSi₂ were studied. It is shown that the predominant orientation of the bonding of the phases in directionally crystallized eutectics (DE) of the system Si-TiSi₂, observed at the stage of steady-state growth, already appears on the surface of nucleation, which apparently indicates that the nucleation of the phases in the alloys of this system is of an epitaxial character.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 44–48, September, 1987.     

Quantum-vacuum geometric phases in the noncoplanarly curved fiber system

The connection between the quantum-vacuum geometric phases (which originates from the vacuum zero-point electromagnetic fluctuation) and the non-normal order for operator product is considered in the present paper. In order to investigate this physically interesting geometric phases at quantum-vacuum level, we suggest an experimentally feasible scheme to test it by means of a noncoplanarly curved fiber made of gyrotropic media. A remarkable feature of the present experimental realization is that one can easily extract the nonvanishing and nontrivial quantum-vacuum geometric phases of left- and/or right-handed circularly polarized light from the vanishing and trivial total quantum-vacuum geometric phases. Since the normal-order procedure may remove globally the vacuum energy of time-dependent quantum systems, the potential physical vacuum effects (e.g., quantum-vacuum geometric phases) may also be removed by this procedure. Thus the detection of the geometric phases at quantum-vacuum level may answer whether the normal-order technique is valid or not in the time-dependent quantum field theory.Received: 4 February 2004, Published online: 29 June 2004PACS: 03.65.Vf Phases: geometric; dynamic or topological - 03.70. + k Theory of quantized fields - 42.70.-a Optical materials - 42.50.Xa Optical tests of quantum theory     

Intermetallic phases of the Hf−Fe system

An assessment of the phases present in the Hf?Fe system agress well with the phase diagram and yields parameters in general agreement with previous Mössbauer studies. The Hf₂Fe phase exhibits a quadrupole split spectrum whereas the HfFe₂ compound shows magnetic hyperfine splitting.     

Evidence of theB andC superconducting phases in the Bi-Ca-Sr-Cu-O system

Summary A sintering process of Bi−Ca−Sr−Cu−O superconductor is reported. The electrical and microstructural analysis of the pellets shows the coexistence ofB andC phases with transition temperatures of about 85 K and 105 K, respectively.     

New phases in the phase transition in amorphous InSb films

In this paper the structures in the process of the phase transition in amorphous InSb film condensed at low temperature are studied by X-ray diffraction experiments. The highest T_c = 4.18 K is as a result of hexagonal phase. The results of the conductance and the critical temperature are explained by means of the experiments of X-ray diffraction in the process of phase transition.     

Effect of orbital degeneracy on the magnetic phases of manganites in the electron doping region

The carrier electronic spectrum E(k) calculated with inclusion of orbital degeneracy of the manganese e _g band for the main types (A, G, and C) of antiferromagnetic ordering in La_1-y Ca_yMnO₃ was employed to derive the total energies of various magnetic configurations for the electron doping region y>0.5. To find the magnetic configuration with the minimum total energy, this energy was minimized with respect to the angle between the spins of Mn⁴⁺ ions belonging to two different magnetic sublattices. The manganite phase diagrams obtained in this way for T=0 K depend on the Heisenberg interatomic exchange parameter J _AF and the intra-atomic Hund exchange J _H and fit correctly to the available experimental data. The calculations show that if the e _g-level splitting is taken into account, there is no magnetic-sublattice canting for equilibrium A and C phases in the region of realistic values of the parameters 0.012<J _AF/t<0.02 and J _H/t=1.7. Transition to the ferromagnetic state through the double-exchange mechanism is energetically favorable only for the G phase with increasing electron concentration. However, already for x≤0.1, the collinear phase C becomes dominant and this transition does not occur.     

Flow-field measurements of liquid and gaseous phases in the ultra-dense region of diesel sprays

The velocities of both the liquid and the gaseous phases in a diesel spray are determined for the first time simultaneously via laser flow tagging (LFT). The experimental setup and uncertainties introduced by seeding particles in the gas phase are greatly reduced by using phosphorescent tracer molecules, i.e. acetone and biacetyl, for the gaseous phase. In addition, simultaneous droplet velocimetry is achieved by doping the liquid fuel with a lanthanide–chelate complex.The relative velocity of gas and liquid phases can be determined from the data on the spray axis close to the nozzle for the first time. This is an important quantity for modeling droplet break-up and evaporation in ultra-dense sprays.PACS 42.62.-b; 47.61.Jd     

New effects in the ISR region

We suggest that the increase of total cross sections and large P_T effects observed over the ISR range have a common origin in the hard collision of parton pairs. The observed magnitude of these effects suggest a parton-parton cross section ～ 0.2 mb. The data is consistent with vector gluon exchange mechanisms. These mechanisms can also cause inhibited shrinkage and energy dependent dips in differential cross sections.     

Glass-forming region in the Cd-Si-As system

Preparation of bulk glasses on the Cd-Si-As base is described and the glass-forming region of this system is defined. Temperatures of the characteristic phase transitions are determined by means of DTA. The melting and solidification of CdSiAs₂ are studied in detail and it is shown that they are incongruent and complex.Cukrovarnická 10, Praha 6, Czechoslovakia.The authors thank to Mrs. Beránková for the preparation of the samples and ot Mrs. Míková for performing the X-ray analysis.     

Magnetic and electrical properties of intercalated phases in the (Cr, Cu)-HfSe2 system

It has been shown that intercalation of the HfSe₂ compound with chromium atoms results in an increase in the magnetic susceptibility and a decrease in the resistivity while retaining the semiconductor conductivity type. The Cr _x HfSe₂ compounds exhibit a paramagnetic behavior at temperatures above 2 K in the entire concentration range 0 ≤ x ≤ 0.25. It has been revealed that an increase in the electron density due to additional introduction of copper can cause the appearance of a cluster-spin-glass-type state in Cr _x Cu _y HfSe₂ compounds. The data obtained indicate a large role of the indirect exchange interaction via conduction electrons in the formation of the magnetic state in layered intercalated compounds based on transition metal dichalcogenides.     

New superconducting phases in field-induced organic superconductor lambda-(BETS)2FeCl4

We derive the parallel upper critical field, Hc2, as a function of the temperature T in quasi-2D organic compound lambda-(BETS)2FeCl4, accounting for the formation of the nonuniform Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state. To further check the 2D LOFF model, we propose to study the Hc2(T) curve at low T in tilted fields, where the vortex state is described by the high Landau level functions characterized by the index n. We predict a cascade of first-order transitions between vortex phases with different n, between phases with different types of the symmetry at given n and the change of the superconducting transition from the second order to the first order as FeCl4 ions are replaced partly by GaCl4 ions.