Probabilities for electronic transitions of molecular systems of high-temperature air components—II. The γ and β systems of NO and the (4+) system of CO

Literature results on absolute and relative probabilities for electronic transitions and on lifetimes of electronically excited states in the γ and β systems of the NO molecule and in the (4+) system of the CO molecule are critically analyzed. The results of previous studies to establish the dependence of the electronic transition strength on the r-centroid for these molecular systems are shown to be inadequate. Using a combined analysis of absolute and relative probabilities, new normalized functions S_e(r_v′v″) are obtained that describe the behaviour of the transition strengths in the spectral ranges occupied by the γ and β systems of NO and by the (4+) system of CO.     

Experimental study of145Cs Decay

The decay of mass separated¹⁴⁵Cs (T _1/2= 0.59 s) was studied. Singles gamma and electron spectra were investigated using Ge(Li) and Si(Li) detectors. A level scheme for¹⁴⁵Ba based on the application of energy sum relations is proposed. The β-branching and logft values for the ground and excited states were deduced from the analysis of γ +ce _? intensity balances. Spin and parity assignments based on transition multipolarities are proposed.     

Effect of plastic deformation of V,Nb and Ta on the superconducting transition temperature and the specific heat coefficients

Specific heat measurements performed between 1.4 and 20 K on bulk and cold-worked V, Nb and Ta superconducting materials are presented. The plastic deformation produces an increase in the superconducting transition temperature T_c, an increase which is relatively less important for Ta than for Nb and less for Nb than for V. An increase is registered for the normal linear coefficient of specific heat γ whereas the Debye temperature decreases slightly. The apparent relation between the increase of T_c and γ suggests qualitatively that the vibrating mobile dislocation contribution is not the only origin of the increase of γ but that a band structure contribution is also to be taken into account.     

Superconductivity and electronic specific heat in V-Mo system

The parameters of superconductivity and specific heat are determined from the low temperature specific heat measurements of V_(1−x)Mo_x (0 ⩽ x ⩽ 1) solid solutions. The coefficient of electronic specific heat γ decreases with increasing Mo concentration and shows a minimum around 80 at. %Mo. Debye temperature θ_D varies slightly over the whole composition range. The superconducting transition temperature T_c also decreases with increasing Mo concentration. The variation of T_c is explained by the variation of γ and discussed in terms of the band structure.     

Low temperature specific heat of Cr-Fe-Si alloys

Low temperature specific heats of Cr-Fe-Si alloys with 3 at. % Si were investigated between 1.4°–4.2°K. The electronic specific heat coefficient γ essentially varies with transition metal electron concentration ( e/a) in the same manner as the Cr-Fe alloys but with the high γ peak slightly shifted to lower e/a. The shift of γ peak suggests transfer of electrons from Si atoms to the 3d magnetic subband of the transition elements.     

Electrostriction in a uniaxial ferroelectric with second order phase transition

The electrostriction constant γ(m²V^?2) of a uniaxial ferroelectric with a second order phase transition has been calculated as a function of the dielectric constant (?P/?E)₀. The results have been experimentally verified on triglycine sulphate (TGS) by measuring γ and (?P/?E)₀. A sign reversal of γ above the Curie temperature is presented.     

Energy expression of the chemical bond between atoms in metal oxides

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, ΔE_M for metal atom and ΔE_O for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the isolated neutral atom, M and O, respectively. In this study, a ΔE_O vs. ΔE_M diagram called atomization energy diagram is first proposed and used for the understanding of the nature of chemical bond in various metal oxides. Both ΔE_M and ΔE_O values reflect the average structure as well as the local structure. For example their values vary depending on the vertex, edge or face sharing of MO₆ octahedron, and also change with the overall density of binary metal oxides. For perovskite-type oxides it is shown that the ΔE_O value tends to increase by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the 〈1 0 0〉 displacement-type transition. The bond formation in spinel-type oxides is also understood with the aid of the atomization energies. The present approach based on the atomization energy concept will provide us a new clue to the design of metal oxides.     

X-ray emission study of the electronic structure of nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Valence states of metal ions and the phase composition of nanocrystalline Al₂O₃ (of the original oxide and the oxide irradiated by high-energy Fe⁺ ions) are studied by using x-ray emission Al L_{2, 3} and O Kα spectra. It is established that the shape of the Al L_{2, 3} spectra strongly changes as one goes from the original (bulk) Al₂O₃ to nanocrystalline oxide, while the O Kα spectra remain practically unchanged. Moreover, irradiation by high-energy Fe⁺ ions results in slight additional changes in the x-ray spectral characteristics of the aluminum oxides under study. The obtained experimental data are compared with the results of theoretical calculations of the electronic structure of α and γ phases of Al₂O₃ performed using the LDA formalism. Using the results of x-ray spectral studies, electronic structure calculations, and x-ray diffraction analysis, it is shown that the revealed spectral differences between the nanocrystalline state of aluminum oxide and the bulk material can be interpreted as a phase transition from the α phase to the γ phase of Al₂O₃ with an addition of bayerite.     

Mössbauer effect study of hyperfine interactions in145Nd

The magnetic hyperfine splitting of the 72.5 keV γ rays of¹⁴⁵Nd was investigated in intermetallic compounds of Nd and in the paramagnetic salts Nd _x Y _1-x Cl₃·6H₂O (withx=0.02 andx=0.05) at 4.2 K. With the magnetic hyperfine tensorA of Nd_0.01Y_0.99Cl₃·6H₂O known from EPR spectroscopy, the analysis of the unresolved magnetic hyperfine spectra yieldsI _e =5/2 for the spin of the 72.5 keV state, in contradiction to a previous result. The multipolarity of the 72.5 keV γ transition was found to be essentiallyM1 with δ²=0.010±0.014, and the magnetic moment of the 72.5 keV state was determined as μ(5/2)=?0.319±0.004 nm. For various divalent and trivalent Nd compounds as well as for metallic Nd the isomer shift IS of the 72.5 keV γ line was measured. A value for the change of the mean square nuclear charge radius during the 72.5 keV γ transition of Δ〈r ²〉=+(1.9±0.9)·10^?3fm² was deduced using electron density differences from free-ion Hartree-Fock calculations.     

Rotational constants for HCN and DCN

Microwave measurements of rotational transitions within vibrationally excited states of several isotopic species of HCN have given improved values for the pertinent B_v constants. These new data have been combined with infrared measurements given in the literature (ncluding D_v terms) to arrive at a set of rovibrational constants (α and γ constants) which is consistent with all available data. Bond distances resulting from several different B_e approximations are intercompared to assess the variability of the r_e values and the importance of the γ terms. The latest r₀ and r_s bond distances are also given.     

<Emphasis Type="Italic">Ab initio</Emphasis> calculations of the superconducting transition temperature for NbC at various pressures

Ab initio calculations of the superconducting properties have been performed for niobium carbide (NbC) at normal pressure and upon a 15 and 30% compression. Factors accounting for the relatively low values of the transition temperature T _c in transition metal carbides are considered and the possible ways of increasing this parameter are discussed.     

Magnetic and electrical properties of several equiatomic ternary U-compounds

Magnetisation, specific heat, electrical resistivity, magnetoresistivity and Hall effect were measured for several equiatomic ternary (1-1-1) intermetallic compounds of formula RTX with R = U, Th, Hf and Ti, T a transition metal (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au), and X = Al, Ga, Sn and Sb. These compounds crystallize in three different crystal structures: the cubic MgAgAs-type, and the hexagonal Fe₂P- and CaIn₂-types. All U-compounds, which we focus upon in this paper, exhibit magnetic moments of about 3μ_B/U at high temperature and encompass U-U distances from 3.51 to 4.68 Å. For the compounds which the largest U-U distances, Kondo-lattice behaviour was observed. The specific heat coefficient γ shows typical metallic values with some enhancement. Remarkably these compounds have an electrical resistivity up to three orders of magnitude larger than that expected and usually found for U-based intermetallic compounds. The Hf- and Th-based compounds serve as nonmagnetic reference materials, however, they also exhibit anomalously larger resistivities.     

Angular dependence of the Knight shift, electric field gradient, and spin-lattice relaxation time of 9Be NMR in beryllium metal

Angular dependences of ⁹Be NMR (±1/2) and (±1/2 ? ±3/20 transition frequencies are measured in a single-crystal beryllium metal plate in a field of 7.04T. The isotropic K _iso and anisotropic K _aniso components of the Knight shift are determined. The measured values of K _iso and T ₁ are considered in terms of the contact, polarization, and orbital contributions.     

Magnetic behaviour of TbMnFe

Neutron diffraction and M?ssbauer measurements have been carried out on the cubic Laves phase intermetallic TbMnFe. The magnetic moment on the transition metal atom is found to be low, 0.2μ _B, at room temperature. This moment is temperature independent down to 10 K. Magnetic moment on the rare earth atom varies from 2.5μ _B at 296 K to 7.27μ _B at 10 K. M?ssbauer spectra recorded at 298 K and 78 K have magnetic character but there is a large distribution of hyperfine field values. Both these features arise due to magnetic frustration created in the sample due to the competing ferro and antiferromagnetic interactions between the transition metal atoms.     

Electrical relaxation in pure and alkali metal thiocyanate complexed poly(ethylene oxide)

Audio frequency complex admittance and DSC studies have been performed on pure poly(ethylene oxide) (PEO) and PEO complexed with alkali metal thiocyanates over the temperature range 5.5–380K. The dielectric constant of the complexed materials is found to be greater than for pure PEO. A discontinuity in the conductivity is found which increases in temperature as the size of the cation increases. In every case, the discontinuity is associated with a feature in the DSC results. Next, some evidence is given that water may enhance the formation of amorphous complexed PEO. In pure PEO, α_a and γ relaxations are observed in good agreement with previous work. A thermal anomaly is found corresponding to α_a. In addition, α_c is identified in pure PEO. Very little difference is found for the γ relaxation between pure PEO and PEO-LiSCN and PEO-NaSCN. For PEO-KSCN, three distinct peaks are found in the γ relaxation region. These results are consistent with a tg⁺t ? tg^-t transition interpretation for γ where the cations reside within the helical channels at low temperatures.     

First order β, γ phase transition in NH4Br

The course of the order parameter around the β, γ phase transition (235 K) in the NH₄Br has been closely observed by means of linear optical birefringence. The experimental data were fitted in the critical region T > 0.9T₀ by the Landau theory and a simple power law. Both relations reveal a first order transition, with the jump height in the birefringence amounting to Δn(T₀)/?Δn(120 K) = 0.145.     

The contact charge density of conduction electrons of Fe in Co metal as derived from internal conversion

From an internal-conversion measurement of the 14.4 keV transition ⁵⁷Fe, the contact 1 charge density of conduction electrons for Fe in Co metal was obtained to be ?_4s(0) = 4.6 ±0.4 a₀⁻³, which is close to theoretical values but is smaller than that for Fe in Fe metal obtained recently.     

Winkelkorrelationsmessungen an88Sr

The γγ ande _? ^KL γ directional correlations have been measured for the (898–1836) keV cascade in⁸⁸Sr following the decay of⁸⁸Y. The observed correlation coefficients areA ₂₂(γγ)=?0.0784±0.0042 andA ₂₂(e _? ^KL γ)=0.0102±0.0046. The γγ experiment is consistent with a mixing ratio δ(γ)=0.009±0.005 for the 898 keV transition. Using the result of thee _? ^KL γ experiment the most probable value of the ratio of the penetration matrix element to the normal γ-ray matrix element was determined to be η=0.03±0.30 showing a normal conversion process. This penetration parameter agrees with a hindrance factorH _W(E1)=2.1 · 10^?3 for theE1 transition.     

Light induced molecular magnetic polaron in EuO

Stoechiometric EuO samples do not present insulator metal transition below Curie temperature (T_c = 70 K). Experimental data presented in this paper show that when these samples are illuminated, it appears: an insulator metal transition below T_c, and, at room temperature, a decrease of activation energy, as well as a small increase in conductivity. Oxygen deficient samples exhibit usually this insulator metal transition. When they are illuminated room temperature activation energy remains unchanged, and the insulator metal transition is more important. These results cannot be explained by means of a free electron model. Electrons are photoexcitated from 4? levels, or donor levels, to conduction band. Then, these electrons polarise Eu²⁺ spins and make magnetic polarons. These polarons cannot be “Bound Magnetic Polarons” because samples do not contain oxygen vacancies. In addition these polarons would be stable until room temperature. Thus, they are expected to be “Molecular Magnetic Polarons”. Our results confirm then this model proposed by Kusuya.