High-pressure phases and pressure-induced phase transition of MoN6 and ReN6

Transition metal nitrides have been widely used in many scientific and technical areas because of their unique physical and mechanical properties. We report two new nitrogen-rich transition metal nitrides, MoN₆ and ReN₆, by crystal structure searching technique. Under high pressure, MoN₆ will undergo phase transition (from R-3m to Pm-3 phase) at 54 GPa, and ReN₆ always keep the R-3m phase in the pressure range from 50 to 100 GPa. There are benzene-like six-membered “N6” rings with nitrogen single bonds in the R-3m phase structures, indicating that MoN₆ and ReN₆ are expected to be the high-energy-density materials.     

Nuclear charge radii of Al and Si from elastic electron scattering between 25 and 60 MeV

Elastic electron scattering cross sections of²⁷Al and Si (natural isotopic mixture) have been measured relative to carbon. The rms charge radiiR _m , deduced with partial wave calculations, are (3.01±0.05) fm for²⁷Al and (3.06±0.05) fm for Si, in good agreement with results from muonic X-ray energies. The values given are those for a Fermi charge distribution with skin thickness 2.5 fm; harmonic oscillator shell model distributions yield radii smaller by 0.03 fm. The ratioR _m (²⁷Al)/R_m(Si) is 0.984±0.016.     

Beats of quantum oscillations of the hall coefficient and resistivity in semiconductor alloys n-Bi0.93Sb0.07 at a small deviation of the magnetic field direction from the trigonal axis

Quantum oscillations of the resistivity ??₂₂ and Hall coefficient R _12.3 in the semiconductor alloy n-Bi_0.93Sb_0.07 have been studied at H ?? C ₃ and j ?? C ₁ in magnetic fields to 14 T and at temperatures of 1.5, 4.5, 10, and 20 K. At temperatures of 1.5 and 4.5 K, beats of quantum oscillations of ??₂₂ and R _12.3 due to a small deviation of the magnetic field H from the crystallographic C ₃ axis have been observed. To determine the oscillation period ?? _i , cyclotron mass m _ci , cyclotron frequency ?? _ci , and extreme section S _extri, experimentally measured quantum oscillation beats have been compared with the model beats of oscillations of three harmonic functions, two of which have close frequencies. The deviation of the parameters ?? _i , m _ci , and S _extri from the same parameters when the magnetic field H exactly coincides with the trigonal C ₃ axis has made it possible to estimate the magnetic field H deflection angle from the trigonal C ₃ axis, which is ??1°.     

Structural and vibrational properties of PVT grown Bi2Te3 microcrystals

High-quality Bi₂Te₃ microcrystals have been grown by physical vapor transport (PVT) method without using a foreign transport agent. The microcrystals grown under optimal temperature gradient are well facetted and they have dimensions up to ～100 μm. The phase composition of grown crystals has been identified by X-ray single crystal structure analysis in space group R3?m, a=4.3896(2) Å, b=30.5019(10) Å, Z=3 (R=0.0271). Raman microspectrometry has been used to describe the vibration parameters of Bi₂Te₃ microcrystals. The FWHM parameters obtained for representative Raman lines at 61 cm^?1 and 101 cm^?1 are as low as 3.5 cm^?1 and 4.5 cm^?1, respectively.     

Binding-energy reference in X-ray photoelectron spectroscopy of insulators

The surface potential of a sample in XPS depends on the flux and energy of incident electrons and on the resistance, R, between the surface and the spectrometer. When R is very low, the kinetic energy E_m of the ejected photoelectron, relative to the spectrometer vacuum level, is given by the well known relation E_m=hν φ_Bφ_S, where hv is the photon energy, φ_B the binding energy relative to the sample Fermi level, and φ_S the work-function of the spectrometer. However, when R is very high and the residual charge left by the ejected photoelectron is solely compensated by a sufficient flux of low-energy monoenergetic electrons of energy φ_e, the sample charges to φ_e. The measured kinetic energy is now given by E_m = hνφ_Bφ_R+φ_e, where φ_R, is the work-function of the sample. Consequently, binding energies on insulated samples are measured relative to the vacuum level, not the Fermi level, since E_m now depends on gf_R. A good conductor can be examined both shorted and insulated. The difference in measured kinetic energy is E_m (shorted)E_m (insulated) = φ_Rφ_Sφ_e. This may provide a method for measuring changes in the work-function while monitoring surface composition.     

Structural phase transitions in KCdF3

The successive phase transitions in KCdF₃ have been studied by using X-ray diffraction and differential type thermal analysis. Three transitions are observed at 485, 471 and 243 K; these are of 1st-, 2nd- and 2nd-order respectively. The space groups of the four phases are found, from the high temperature side, to be Pm3m, P4/mbm, Pbnm and Pbnm respectively. The first and second transitions can respectively be explained in terms of the condensation of soft-phonon modes at the M and R points in the cubic Brillouin zone. The third transition may be caused by instability due to titlings of CdF₆ octahedra.     

Phase transitions in polarized samples of multicomponent solid solutions based on lead zirconate titanate

The physical properties of multicomponent solid solutions that are based on lead zirconate titanate and belong to the rhombohedral part of the phase diagram are investigated. The conditions for the existence of the R3c, R3m, and P4mm phases in polarized samples are determined. The region of existence of the relaxor phase is revealed.     

Molecular field theory analysis of R3Co11B4 compounds

The temperature dependence of magnetization of the R₃Co₁₁B₄ compounds has been analysed using the two-sublattice molecular field theory. The molecular field coefficients, n_CoCo, n_RCo, n_RR, have been calculated by a numerical fitting process. The analytic form of the exchange field H_R(T) varying with temperature for each of the R₃Co₁₁B₄ compounds is presented, and some results are discussed.     

Central configurations of the collinear three-body problem and singular surfaces in the mass space

This Letter is to provide a new approach to study the phenomena of degeneracy of the number of the collinear central configurations under geometric equivalence. A direct and simple explicit parametric expression of the singular surface H₃ is constructed in the mass space (m₁,m₂,m₃)∈³(R⁺). The construction of H₃ is from an inverse respective, that is, by specifying positions for the bodies and then determining the masses that are possible to yield a central configuration. It reveals the relationship between the phenomena of degeneracy and the inverse problem of central configurations. We prove that the number of central configurations is decreased to 3!/2−1=2, m₁, m₂, and m₃ are mutually distinct if m∈H₃. Moreover, we know not only the number of central configurations but also what the nonequivalent central configurations are.     

Dynamical study of remanent magnetization in nanoparticles

For collections of noninteracting nanoparticles, we study the reduced static remanent magnetization, m_R, produced by the removal of a saturating magnetic field. We show that, except for special cases such as easy uniaxial anisotropy, m_R depends on both the ramp-down rate of the field and the energy dissipation rate of the spin dynamics. Using the Landau–Lifshitz equation, we illustrate this result with explicit dynamical calculations of m_R for cubic and for mixed cubic–uniaxial anisotropies.     

A new monoclinic phase and elastic effects in PbZr1−x TixO3 solid solutions

The elastic matching of single-or polydomain ferroelectric phases R3m-P4mm, Cm-P4mm, and R3m-Cm and the relaxation of mechanical stresses in PbZr_1?x Ti_xO₃ solid solutions are investigated. The conditions for constancy of the optimum volume concentrations of twin domains of the P4mm and Cm phases in the vicinity of the morphotropic phase boundary in the x-T diagram are analyzed, and the correlation between the morphotropic boundary and interfaces, namely, the planes of zero mean strains, is discussed.     

Intensities and half-widths at different temperatures for the 201III←000 band of CO2 at 4854 cm−1

Measurements made at temperatures of 197, 233, and 294°K of the absolute intensities and self-broadening coefficients for the vibration-rotation lines of the 201_III←000 band of the ¹²C¹⁶O₂ molecule, are reported. From these measurements, values have been derived for the vibration-rotation interaction factor (F_VR), the purely vibrational transition moment (|R(O)|), and the intensity (S_Band). The results are: E_VR(m) = 1+(2.2±0.7)×10^?3m+(5.6±1.6)×10^×5m², |R(0)| = (2.064±0.017)×10^?3 debye, S_Band = 21,329±69 cm^?1km^?1atm^?1_STP. The results for the self-broadening coefficients are presented in the text.     

The dependence of the radiative transition probability of donor-acceptor pairs on pair separation

The probability W(R) for radiative donor-acceptor pair transitions is generally assumed to decrease exponentially with increasing pair separation R, with a characteristic length a. When one centre in the pair is deep and strongly localized and the other one is shallow, a equals half the Bohr radius of the shallower centre. For pairs in GaP involving two shallow centres we have previously reported that a exceeds half this Bohr radius, and have suggested this to be due to the spatial extent of the deeper centre. In the present paper we investigate this point, both experimentally, and by considering Novotny's calculations — for direct transitions — on the R-dependence of W(R), in which the Bohr radii of both donor and acceptor are parameters. According to these calculations, W(R) is not exponential in the case of two shallow centres. In a limited range of R, W(R) is approximately exponential, however, and theoretical “effective values” of a can be obtained. These effective values are compared with experimental data on a for the pair series S_P-Si_P, S_P-Cd_Ga, S_P-Zn_Ga and S_P-C_P in the indirect semiconductor GaP; a amounts to ∽ 5.4, 7.0, 7.7 and 9.1 Å, respectively. The comparison shows that the difference found between the experimental a and half the Bohr radius of the less localized centre in the pair can indeed be explained by the influence on a of the spatial extent of the more localized centre. This findings implies a non-exponential W(R) for pairs with two shallow centres. This conclusion depends critically on the values used for the Bohr radii of the acceptors, however. These are not accurately known, due to insufficient knowledge of m¹_h, one of the quantities needed in calculating the radii. We used m¹_h = 0.36 m₀ to 0.40 m₀, corresponding to the normally used hydrogen-model energy of 40–45 meV. An alternative explanation for the experimental values of a is that in reality m¹_h is significantly lower than the 0.36 m₀ to 0.40 m₀ used, leading to larger acceptor Bohr radii and, in the extreme case, to no influence on a of the more localized centre and to an exponential W(R). In order to decide between the two possible explanations, additional experiments are presented. These include an accurate comparison of a between S_P-C_P and O_P-C_P as well as between S_P-Zn_Ga and O_P-Zn_Ga pairs. This is done by analysing the intergral band decay and time-resolved spectra of these pairs. The conclusions for all pairs mentioned are: (i) The Bohr radius of the acceptors involved is significantly larger than calculated from an effective-mass energy of 40–45 meV; they correspond to a hydrogen-model energy of 28 meV (m¹_h = 0.25 m₀). (ii) There is in first approximation no influence on the shape of W(R) of the spatial extent of the more localized centre. (iii) The experimental results are well described by an exponential W(R) with a equal to half the Bohr radius of the less localized centre of the pair.     

Study of the electric field gradient at <Superscript>111</Superscript>Cd in the <Emphasis Type="Italic">R</Emphasis>Al<Subscript>3</Subscript> compounds synthesized under high pressure

The electric quadrupole interaction parameters for impurity ¹¹¹Cd nuclei in intermetallic RAl₃ compounds (R = La, Ce, Sm, Gd, Tb, Dy, Ho, Er, Yb, or Lu) synthesized under high (8 GPa) pressure at high (1800–1900°C) temperatures have been measured using the method of perturbed angular γγ correlations. It has been established by X-ray diffraction analysis that with an increase in the atomic number of the R element the obtained high-pressure phases are crystallized successively in the orthorhombic, hexagonal, and cubic structures. In the compounds with R = La, Ce, Sm, and Gd, deviation from the known structural types and formation of new ones due to the change in the stoichiometric composition have been observed. The data obtained by the method of perturbed angular γγ correlations have confirmed deviation from the specified stoichiometric composition 1R: 3Al for the LaAl₃, CeAl₃, SmAl₃, and GdAl₃ compounds and verified the correctness of the stoichiometric composition and the presence of the Cu₃Au structural type for the remaining RAl₃ high-pressure phases.     

Characteristics of degenerated four wave mixing in ZnS/CdSe/ZnS quantum dot quantum well with multi-shell structure

The wave functions and eigenenergies of electrons in ZnS/CdSe/ZnS cylindrical quantum dot quantum well (QDQW) have been calculated by solving a three-dimensional nonlinear Schrödinger equation, in the framework of the effective-mass envelope-function theory. The third-order susceptibilities of the degenerated four waves mixing (DFWM) have been calculated theoretically by means of compact density matrix. The third-order susceptibilities as the function of the shell radius R₂, R₃ have been analyzed. The results show that the magnitude of nonlinear susceptibility is increased with the increasing of well radius. The resonance frequency of the photon have a shift when R₂ or R₃ is increasing and the relation between nonlinear susceptibility and relaxation time has also been studied.     

Majorana masses,photon gas heating and cosmological constraints on neutrinos

Non-vanishing Majorana masses generally lead to flavor-changing neutral currents in the neutrino sector. It is shown that when both right- and left-handed neutrinos have non-vanishing Majorana masses (M_R≠0 and M_L≠0), flavor-changing neutral currents could be as large as flavor-diagonal ones. However, when only right-handed neutrinos have non-vanishing Majorana masses (M_R≠0 but M_L=0), flavor-changing neutral currents are small. If M_R?D (Dirac masses), they are of $\text{O}\text{((}\text{D}\text{M}{}_{\mathrm{<mtext>R</mtext>}}\text{)}{}^2\text{)}$. If M_R?D, they are $\text{?(}\text{m}{}_{\mathrm{<mtext>L</mtext>}}\text{m}{}_{\mathrm{<mtext>H</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, where m_L and m_H are masses of light and heavy neutrinos appearing in a flavor-changing process.By using these results we examine cosmological implications of non-vanishing flavor-changing neutral currents. Heavy neutrinos can decay into three light neutrinos at an appreciable rate by exchanging a Z-boson. It is demonstrated that owing to this decay mode, heavy neutrinos of mass larger than 70 keV but less than 2m_e give rise to no contradiction with the standard big bang cosmology in the most general case.We also show that if there exist heavy neutrinos of mass m_H2m_e, their decay at an early era of the universe induces photon gas heating, which alters Cowsik and McClelland's constraint on light neutrino masses to Σm_L < k · 100 eV with the sum running over all Majorana eigenstates. Here the constant k, representing the heating effect of the photon gas, is restricted by the deuterium abundance of the present universe. For instance, Σm_L < 240 eV for m_H ～ 25 MeV and the present baryon density = 3.4 × 10^?31 g · cm^?3.     

Model calculation of amplitudes for FT-ICR ion detection in a cylindrical Penning trap

A Green’s function strategy first proposed by Grosshans et al. is used to calculate the electric charges induced by trapped ions on the 4-fold or 8-fold segmented ring electrode of a cylindrical Penning trap. The ions are assumed to move in the central region of the trap where the harmonic approximation holds. The electric charges induced on each detection segment of the ring electrode are obtained in the form of a triple Fourier series with coefficients that describe the contribution of each frequency combination m ₊ ν ₊+m _? ν _?+m _z ν _z as a function of R ₊, R _?, Z, where ν ₊, ν _?, ν _z are the characteristic frequencies and?R ₊, R _?, Z the corresponding amplitudes of the ion motion. The sideband structure is analyzed and the origin of the sidebands is tracked. Finally, single-electrode, differential, and additive detection are discussed.     

Anomalous Hall effect in (Co41Fe39B20) x (Al-O)100 − x nanocomposites

The concentration dependence of the coefficient R _s characterizing the anomalous Hall effect (AHE) has been studied by measuring the electrical resistivity ρ, magnetoresistance, and the magnetic field dependence of magnetization and Hall resistivity of (Co₄₁Fe₃₉B₂₀) _x (Al-O)_{100 ? x} nanocomposite thin films. It has been demonstrated that the AHE coefficient increases by more than an order of magnitude with a decrease in the percentage x of the amorphous ferromagnetic metal from 60 to 30 and its behavior is described by the relation R _s ～ ρ ^m , where m = 0.46 ± 0.1. At the same time, the coefficient characterizing the normal Hall effect grows by a factor of less than 10. The mechanisms underlying the giant Hall effect in nanocomposites have been discussed.     

The entropy change on melting of simple substances

It is shown that the volume independent component, R 1n 2, of the entropy of melting, ΔS_m, for argon persists, unchanged, some distance into the fluid phase as a configurational entropy. For argon, sodium, and caesium in its normal melting regime ΔS_m = Rln 2 + αB_TδV_m, where ΔV_m is the volume change on melting and αB_T is the temperature independent product of the thermal expansion coefficient and the isothermal bulk modulus.     

Hall coefficients for A15 compounds: Nb-Sn and V-Si

The Hall coefficients, R_H, for A15 structure single crystal V₃Si and polycrystal V25.25 at.% Si and Nb 26 at.% Sn have been measured as functions of temperature. The data between the superconducting transition temperature, T_c, and 80 K for the Nb-Sn show a small dip centred arounf 30 K which accompanies a cubic-to-tetragonal lattice distortion commencing at about 45 K. R_H for the VSi samples, which are believed to be non-transforming, is temperature independent in the range 17–40 K and equal to 2.0 ± 0.2×10^?10m³C^?1. These result are discussed in relation to the effect of the tetragonal distortion on the band structures of these compounds.