Study of the Absorption Characteristics of Transitions in the HOT 2υ2–υ2 Band of the 34SO2 Molecule

Russian Physics Journal - The absorption coefficient of the rovibrational 2υ2–υ2 band of the 34SO2 molecule localized in the region 350–850 cm–1 is studied for the first...     

SDW in the 2D Compound CuFeTe2

In a previous work (ICAME'97) we presented the Mössbauer results for a non-stoichiometric sample of the quasi-two-dimensional (2D) dichalcogenide CuFeTe₂, where a Spin Density Wave (SDW) ground state with T _SDW=256±15 K was proposed. Here we report the study of the magnetic and electric properties determined by magnetic susceptibility, Mössbauer spectroscopy and resistance measurements, of an almost stoichiometric sample prepared by the vertical Bridgman growth technique. The SDW behavior is supported by the results obtained by the following different techniques: Magnetic susceptibility: A magnetic transition is observed at T _SDW=308 K with a Pauli paramagnetic behavior above this temperature. Mössbauer effect: The shape of the spectra and the thermal evolution of the hyperfine field are characteristic of the SDW's in quasi-2D systems. Electrical resistance: There is a metal–semiconductor transition along the layers as the temperature decreases indicating the opening of a gap at the Fermi level.     

Quantum critical behaviour in the CePd2Si2/CeNi2Ge2 system

We have explored the vicinity of the antiferromagnetic quantum critical point in the related heavy fermion metals CePd₂Si₂ and CeNi₂Ge₂ as a function of hydrostatic pressure. The normal state resistivity of the antiferromagnet CePd2Si2 near the critical pressure, at which magnetic order disappears, varies as ρ ～ T^χ(1:1 < χ < 1:4) over nearly two orders of magnitude in temperature up to about 30 K. This anomalous form for the resistivity appears to defy not only Fermi-liquid theory, but also simple phenomenological models for the effect of spin fluctuations close to a quantum critical point. An analogous unconventional behaviour is observed in the ambient pressure resistivity of the electronically and structurally equivalent, non-magnetic metal CeNi₂Ge₂. At pressures above 15 kbar, a new and unexpected superconducting transition appears in CeNi₂Ge₂ below 220 mK, which rises to higher temperatures with increasing pressure, reaching 400 mK at 26 kbar.     

Vibrational–Rotational Analysis of the Hot 2ν2–ν2 Band of the 15NH2D and 15NHD2 Molecules

Optics and Spectroscopy - High-resolution spectra of the $$2{{\nu }_{2}}{-} {{\nu }_{2}}$$ hot band of the 15NH2D and 15NHD2 molecules are investigated for the first time. The analysis is carried...     

Accumulating evidence for the two-step magnetic ordering in the borocarbides DyNi2B2C and DyCo2B2C

Accumulating evidence for a two-step magnetic ordering in the borocarbide DyNi₂B₂C is summarized, including earlier overlooked evidence for the initial magnetic transition and a recent magnetization study of polycrystalline samples. The two-step ordering involves initial two-dimensional ferromagnetic ordering in the DyC (basal) planes at T_N (=16.3 K), gradual build-up of the three-dimensional (3D) alternate stacking of ferromagnetic planes, and a final 3D ordering in the AF–I-related structure at a lower temperature T_o (=10.4 K), depicting a first-order transition. Supporting evidence for the two-step magnetic ordering in DyNi₂B₂C comes from point-contact spectroscopy measurements in the normal state for DyNi₂B₂C–Ag contact, and from similar behaviour of PrNi₂B₂C and (Pr_0.91Dy_0.09)Ni₂B₂C. In the isostructural borocarbide DyCo₂B₂C the two magnetic transitions (at 7.8 and 2.6 K) deduced from the specific-heat measurements are also attributed to a two-step magnetic ordering.     

Zeeman effects in the visible 2B2 ← 2A1 system of NO2

The Zeeman effect facilitates certain rotational assignments in bands of the ${}^2\text{B}{}_2\text{-}{}^2\text{A}{}_1$ electronic system of NO₂. A partial analysis of two bands of this system is reported.     

Structure of the energy bands in semiconductors of the AIBIIIC2 VI type AgInS2, AgInSe2, AgInTe2

The energy-band structure of the compounds AgInS₂, AgInSe₂, AgInTe₂ is calculated. These compounds are found to have a simple type of conduction band, which consists of several competing maxima lying at different points of the Brillouin zone.     

Density functional study of the polymorphism of Cs2C2 and Rb2C2

By density functional theory-based calculations it is shown that in the athermal limit the orthorhombic polymorph of Cs₂C₂ is more stable by ≈7 kJ/mol with respect to the hexagonal modification, while the energy difference between the corresponding two Rb₂C₂-polymorphs is about 4 kJ/mol. The calculations do not corroborate the experimental finding of unusually long and short C-C bond lengths in Cs₂C₂ at low temperatures. This theoretical result is supported by calculations on monomeric LiCCH, where DFT calculations give all bond lengths within 1%.     

Low-temperature electron microscopy of the surface of the superconductor Bi2Sr2CaCu2O8

Electron microscopy studies of the microstructure and composition of the surface of the high-temperature superconductor Bi₂Sr₂CaCu₂O₈ are performed. The secondary-electron emission intensity and its temperature dependence are estimated in local regions at temperatures lower than 300 K. The results are interpreted within the secondary-electron emission model.     

Study of the superionic system AgI-PbI2-Ag2O-B2O3

The superionic system AgI-PbI₂-Ag₂O-B₂O₃ with two compositions has been prepared. The pelletised samples were investigated with regard to conductivity, modulus and dielectric analysis at various temperatures and frequencies. The activation energy determined for the samples was found to be varying between 0.09 to 0.10 eV. The effect of polarization at the electrode has been analyzed from conductivity spectra. From the impedance and modulus analysis it has been found that the system is non-ideal and there exists a distribution of relaxation times which is independent of temperature.     

Study of the modulated structure of Bi2Sr2CaFe2Ox

The ceramics and single crystals of the Bi₂Sr₂CaFe₂O_x compound were synthesized. The X-ray diffraction data showed orthorhombic symmetry. The lattice parameters are equal toa=5.464 Å,b=5.453 Å,c=31.313 Å. The crystal structure is described by the primitive Bravais lattice with the possible space groups Pbmm. Pbm2 and Pb2₁m. The obtained X-ray patterns show the presence the incommensurate structural modulation with the following parameters: the modulation vector lies in the (100)-plane, the value of the wave-vector componentq _b=0.22(3). The comparison of the obtained results with data for Fe-doped Bi₂Sr₂CaCu₂O_x and Bi₂Sr₃Fe₂O_x are presented. No magnetic peculiarities of the compound were found. Mssbauer measurements of the ceramic samples indicate the presence mainly of Fe³⁺ oxidation state and Fe⁴⁺ (about 20%). The decrease of the quadrupole-splitting values for 2212Fe in comparison with Fe-doped 2212Cu was revealed that may be connected with higher symmetry of the local environment of Fe atoms in 2212Fe.     

Toward the 2s-2p spectroscopy of the µp atom

Very recent results relevant to the planning of laser spectroscopy of the 2s-2p splitting in the µp atom are presented. An experimental configuration providing a sufficiently small muon stopping volume at the lowest pressures has been tested. The first experimental indications for the existence of a long-lived 2s fraction at low pressure are discussed.