Theory of solid solubility for rare earth metal based alloys

Both parabola and ellipse separating schemes are used to study the solid solubilities for the binary alloy systems based on the 13 rare earth metals. It has been found that the soluble elements can be separated from the insoluble ones by a parabolyy ₁=a−bx ₁ ² or an ellipse(x ₂−m)²/c²+(y₂−n)²/d²=1. The results show that the overall reliabilities of the solid solubilities for the 897 binary alloys based on the rare earth metals are 89.2% and 92.8% for the parabola and ellipse regularities respectively. The constants a and b in the parabola equation, andm, n, c andd in the ellipse equation are discussed, which can be related to some appropriate parameters for each host metal respectively.     

Atomic parameter model for the solid solubilities in binary transition metal based alloys

Based on the same method by us which describes the solid solubilities of the binary nontransition metal based alloys, the solid solubilities at room temperature in 1380 binary alloys which are based on the 23 transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re, Os, Ir and Pt) of the fourth, fifth and sixth long periods have been studied in this paper. It has been found that the soluble elements can be separated from the insoluble elements by an ellipse equation (x−m) ²/c ²+(y−n) ²/d ² = 1, by using a criterion of 0.5at% solubility at room temperature for every host element. The results show that the overall reliability for the ellipse equation is up to 90% for the 1380 alloys, which indicates the theoretical results are very good in agreement with the experimental data. The parameters m, n, c and d in the ellipse equation can be explained by the appropriate parameters for every host metal.     

Electronic structure of the metallic tungsten bronces Lax−yGdyWO3 (ESR measurements)

ESR- and magnetic susceptibility measurements on the metallic bronce La_x?yGd_yWO₃ (x = 0.10, 0.15; y ? x) prove that the 6s²5d¹ orbitals of the rare earth (RE) ions do not contribute to the conduction band of the WO₃ complex. The RE ions are completely decoupled from it; crystal field effects, therefore, are observable.     

Coercivity of single-domain nickel wires

The coercivity H_c of compacts of thin (0.1?5 μ diameter) nickel wires embedded in a silver matrix has been measured as a function of the effective wire radius d_eff. H_c increases linearly with 1/d_eff², in agreement with Aharoni's theory of magnetization reversal by curling. From the slope, δH_{c/gd (deff^?2)}, upper and lower bounds for the exchange constant A of Nickel have been derived (77K): 1.5 × 10^?11 Wsec/m ? 3.0 × 10^?11 Wsec/m.     

EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr5+ ions

The (PO₄)^3? units in a CsH₂PO₄ (CDP) crystal were replaced in a small fraction of sites by (CrO₄)^3? groups and the EPR of the Cr⁵⁺ center was investigated. Splitting of the EPR line appears at T¹_c=245 K, 91 K higher that the ferroelectric transition temperature T_c=154 K. The electronic wave function of Cr⁵⁺ (3d¹) is identified as d_x2_?y2. The d_x2_?y2 function couples with the near protons and the reorientation of this unit in the two possible configurations occurs in the paraelectric phase and breaks the symmetry far above T_c. The observed correlation time 10^?9 sec and associated activation energy ΔU=0.215 eV are discussed.     

New limits on D0 (1.865) production in proton-nucleus collisions at 400 GeV/c

We present final results of a sensitive search for new particles in π^±K^? effective mass spectra observed in proton-nucleus collisions at 400 GeV/c. We establish a limit for D⁰ (1.865) production B_π⁺π^? dσ/dy < 360 nb/nucleon at y_cm^≈ ?0.4. For D?⁰ → π^?K⁺ the limit is 290 nb/nucleon.     

5d and 4ƒ mixing coefficients for rare earth ions in the pure metals and in silver and gold

The contribution to the crystalline electric field (C.E.F.) parameters from 4? character in the conduction electric wave function has been calculated, without the use of mixing coefficients ?_?, for rare earth ions in gold and silver and for the heavy rare earth metals. From experiment we have deduced the value of mixing coefficient ?_d in each case and used this to predict other C.E.F. potentials.Not only can the theory account well for the fact that the observed A₄⁰〈r⁴〉 coefficient is opposite in sign from that calculated using a lattice sum point charge model, in silver and gold, but the absolute value of A₆⁰〈r⁶〉, calculated without the use of any variable parameters, agrees well with experimental values.     

Energy resolved imaging with a stratified phosphor detector

Polycrystalline solid state solutions of Ba_ySr_1 − yCl₂ have been produced; these adopt the cubic fluorite phase for y ≤ 0.30. The cubic structure minimizes optical scattering from grain boundaries, and so for y ≤ 0.30 the materials are transparent, a key advantage for ceramic scintillators and phosphors. The substitution of Sr²⁺ ions with Ba²⁺ ions has the advantage that it substantially increases the x-ray absorption coefficient with respect to pure SrCl₂. Additional doping with rare earth ions such as Sm²⁺ and Eu²⁺ gives bright x-ray phosphor materials. The Sm or Eu-doped materials show a broad 4f⁵5 d¹ → 4f⁶ emission peaked at 685 nm or a broad 4f⁶5 d¹ → 4f⁷ emission peaked at 406 nm respectively. These materials have been tested as x-ray phosphors and the spatial resolution was determined to be at least 6 LP/mm, whilst the x-ray radioluminescence intensity is around 40% that of the commercial x-ray phosphor Gd₂O₂S:Tb. A stratified phoswich structure, comprising Eu and Sm-doped layers of Ba_ySr_1 − yCl₂ was produced in which the relative intensities of the two emissions varies with x-ray beam energy; this can be used for energy discrimination in imaging by way of emission spectra as opposed to the more commonly used pulse shape discrimination. A dual energy imaging technique based on these bi-layered structures and utilizing a semi-professional grade digital SLR camera is described and composition-sensitive imaging has been demonstrated.     

Spin-0 and spin-1/2 particles in a constant scalar-curvature background

We study the Klein-Gordon and Dirac equations in the presence of a background metric ds²=−dt²+dx²+e^−2gx(dy²+dz²) in a semi-infinite lab (x>0). This metric has a constant scalar-curvature R=6g² and is produced by a perfect fluid with equation of state p=−ρ/3. The eigenfunctions of spin-0 and spin-1/2 particles are obtained exactly, and the quantized energy eigenvalues are compared. It is shown that both of these particles must have nonzero transverse momentum in this background. We show that there is a minimum energy E²_min=m²c⁴+g²c²?² for bosons (E_KG>E_min), while the fermions have no specific ground state (E_Dirac>mc²).     

Error propagation in extrapolated nuclear mass predictions

The properties of the error of the nuclear masses calculated from the transverse mass relations are analysed. The work assumes that the calculated errors of the nuclei whose masses are known experimentally behave as a sample selected randomly from a normal population having a zero mean and a standard deviationσ. It is found that the errors of the calculated masses of nuclei far from the line of beta-stability behave asc ₁ d ^3/2 wherec ₁ is a constant andd is the distance of the nucleus from the line of beta-stability. It is shown also that the errors related to the calculated mass differences behave asc ₂ d ^1/2 wherec ₂ is another constant.     

Preparation,stoichiometry and magnetic properties of Cu y Cr2Se4−z Br x spinels with 0.5≲x≲2

The chemical composition of Cu _y Cr₂Se_4?z Br _x spinels depends strongly on the preparation parameters. Spinels with 0.8?y?1.2, 0.5?x?2, and 0?z?x?0.2 have been prepared. Whereas the lattice constanta _o of these spinels differs only by less than approximately 0.6%, their Curie temperatureT _c depends sensitively on the spinel composition. For Cu_1.1Cr₂Se_3.4Br_o.46,a _o=1.0410 nm andT _c=310 K were found to compared witha ₀=1.0447 nm andT _c=84 K of CuCr₂Se₂Br₂.     

Diffusionskonstante und charakteristische Absorption vor der Bandkante von Mn in ZnO-Kristallen

ZnO single crystals were doped with Mn and Co by diffusion. In the temperature range from 1400–1600 K the Mn and Co-diffusion-constants were determined:D _Mn=3.2 · 10^?3 exp (?2.87 eV/kT) cm² sec^?1 andD _Co=1·10exp(?3.98 eV/kT) cm² sec^?1. The Mn doped ZnO crystals show a characteristic colour due to an absorption near the intrinsic absorption edge. The corresponding absorption spectra were measured forE⊥c andE∥c. A discussion of different absorption mechanism shows that a charge-transfer transition is responsible for this absorption.     

Electronic structure of the surface of rare Earth metals

A qualitative model describing the surface of rare earth metals with an uncompleted 4f electron shell (Ce-Yb) and the process of thermal evaporation from this surface is proposed. The model is based on a correlation established between the energies of the lowest-lying levels of the 4f^N?15d6s² configuration and the temperatures of equal saturated-vapor pressures of these metals.     

Localization in the ground state of the ising model with a random transverse field

We study the zero-temperature behavior of the Ising model in the presence of a random transverse field. The Hamiltonian is given by $$H = - J\sum\limits_{\left\langle {x,y} \right\rangle } {\sigma _3 (x)\sigma _3 (y) - \sum\limits_x {h(x)\sigma _1 (x)} } $$ whereJ>0,x,y∈Z ^d, σ₁, σ₃ are the usual Pauli spin 1/2 matrices, andh={h(x),x∈Z ^d} are independent identically distributed random variables. We consider the ground state correlation function 〈σ₃(x)σ₃(y)〉 and prove:

1. Letd be arbitrary. For anym>0 andJ sufficiently small we have, for almost every choice of the random transverse fieldh and everyx∈Z ^d, that $$\left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle \leqq C_{x,h} e^{ - m\left| {x - y} \right|} $$ for ally∈Z ^d withC _{x h} <∞.
2. Letd≧2. IfJ is sufficiently large, then, for almost every choice of the random transverse fieldh, the model exhibits long range order, i.e., $$\mathop {\overline {\lim } }\limits_{\left| y \right| \to \infty } \left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle > 0$$ for anyx∈Z ^d.

     

Die Stromdichte eines quadratisch integrierbaren Klein-Gordon-Feldes mit Wechselwirkung

A four vector is constructed for the statistical interpretation of a relativistic scalar wave function which is not a solution of an interaction-free Klein-Gordon equation. The zero component of the four vector is positive definite, whereas the four components satisfy the equation of continuity. It is proved that these components, which are bilinear forms inΨ(x)=∫d ⁴pa(p)e^?ipxsatisfying the normalization condition(2π) ⁴(2m)^?1∫ d⁴pθ(p⁰)θ6(p²)¦a(p)¦²=1 reduce to the four-vector ofPetzold and co-workers if the transition fromΨ(x) to the free-particle wave functionΦ(x)=∫d ³¯pa(¯p)e^?ipxsatisfying(2π) ³ (2m)^?1∫(2p₀)^?1¦a (¯p)¦²d³¯p=1 is made in the proper way. The nonrelativistic limit in the case of relativistic interactions is also discussed.     

K +-meson production inpBe interactions atT p=2.9 GeV

The production ofK ⁺ andπ ⁺ mesons and protons inpBe collisions atT _p=2.9 GeV has been studied at the ITEP proton synchrotron. Ejectiles with a momentum ofp=545 MeV/c were observed under an emission angle ?=17°. The detectors which have been developed for the identification of kaons out of a six orders of magnitude more intense background of pions and protons are described. A cross-section ratio d²σ _K ⁺/dΩdp: d² σ _p /dΩdp: d²σ _p /dΩdp of (1±0.34):(85±1):(31±1) has been measured. Normalization with existing pion data yields an invariant differential cross sectionE·d³σ _K ⁺/d³ p=(3.1±1.2) mbGeV^?2c³sr^?1 and a total cross section of σ_tot(pBe)=(3.7±1.5) mb. These cross sections are compared with existing data and theoretical predictions. TheA dependence ofK ⁺ production in the few-GeV range is analyzed.     

Localization in the ground state of a disordered array of quantum rotators

We consider the zero-temperature behavior of a disordered array of quantum rotators given by the finite-volume Hamiltonian: $$H_\Lambda = - \mathop \Sigma \limits_{x \in \Lambda } \frac{{h(x)}}{2}\frac{{\partial ^2 }}{{\partial \varphi (x)^2 }} - J\mathop \Sigma \limits_{\left\langle {x,y} \right\rangle \in \Lambda } \cos (\varphi (x) - \varphi (y))$$ , wherex,y∈Z ^d , 〈,〉 denotes nearest neighbors inZ ^d ;J>0 andh={h(x)>0,x∈Z ^d } are independent identically distributed random variables with common distributiondμ(h), satisfying ∫h ^?δ dμ(h)<∞ for some δ>0. We prove that for anym>0 it is possible to chooseJ(m) sufficiently small such that, if 0<J<J(m), for almost every choice ofh and everyx∈Z ^d the ground state correlation function satisfies $$\left\langle {\cos (\varphi (x) - \varphi (y))} \right\rangle \leqq C_{x,h,J} e^{ - m\left| {x - y} \right|} $$ for ally∈Z ^d withC _x,h,J <∞.     

Analyticity properties and a convergent expansion for the inverse correlation length of the high-temperatured-dimensional Ising model

We show that the inverse correlation lengthm(β) (= mass of the fundamental particle of the associated lattice quantum field theory) of the spin-spin correlation function 〈s _x s _y 〉,x, y εZ ^d , of thed-dimensional Ising model admits the representation $$m(\beta ) = - ln\beta + r(\beta )$$ for small inverse temperaturesβ > 0.r(β) is ad-dependent function, analytic atβ = 0.c _n , the nth β = 0 Taylor series coefficient of r(β) can be computed explicitly from the Z^d limit of a finite number of finite lattice A spin-spin correlation functions 〈s₀s_x〉t>Afor a finite number ofx = (x ₁,x₂, ..., x_d), ¦x¦ = ∑ _i ^d 1¦x_i¦< R(n), where R(n) increases withn. Furthermore, there exists aβ' > 0, such that for eachβ ε (0,β')m(β) is analytic. Similar results are also obtained for the dispersion curve ω(p), ω(p)=ω(0)=m, pε(-π, π]^d?1, of the fundamental particle of the associated lattice quantum field theory.     

Gleichzeitige Messung von Hyperfeinstruktur,Starkeffekt und Zeemaneffekt des85Rb19F mit einer Molekülstrahl-Resonanzapparatur

A molecular beam resonance apparatus with electric quadrupole lenses asA- andB-fields and with superimposed parallel electric and magnetic transition-fields was used. Molecules in different rotational statesJ, m _J are separated by theA-field. Spectra of molecules in different vibrational states are resolved by their different Starkeffect energies. By this means the following electric and magnetic properties of the molecule could be measured in the rotational stateJ=1 and vibrational statesv=0 and 1: The magnetic and electric dipole moment of the molecule, the scalar and the tensor nuclear dipole — dipole interactiond _s andd _T, the nuclear spinrotational interactionc _F andc _Rb, the nuclear quadrupole interactioneqQ, the nuclear magnetic moment μ_Rb, the anisotropy of the diamagnetic susceptibility ξ_⊥?ξ_∥, the anisotropy of the diamagnetic shielding of the external field by the electrons at the position of the nuclei σ_⊥?σ_∥. Using these quantities it was possible to calculate the quadrupole moment and a weighted quadrupole moment of the electronic charge distribution. The results are: (J=1,v=0) μ_el=8,5464 (17) debμ _J/J=?29,79(2)x10^?6 μ _B d _s/h=0,36(23) kHzd _T/h=0,69(22)kHzc _F/h=10,42(70) kHzc _Rb/h=0,479 (48) kHz.eqQ _Rb/h=?70,3410(26) MHzμ(1?σ_S)Rb=1,3474(5) μ_k (ξ⊥-ξ _∥)=12(6)×10^?30 erg/Gauß² (σ_⊥-σ∥)_Rb=?3,8(2,1)×10^?4 (σ⊥-σ _∥)_F=?2,6(3)×10^?4     

Optical and time-resolved electron paramagnetic resonance studies of the excited states of para-methylcinnamic acid and para-methylcinnamate anion

Time-resolved electron paramagnetic resonance (EPR), fluorescence, and phosphorescence spectra have been observed for the excited states oftrans-p-methylcinnamic acid (p-MeCA) andtrans-p-methylcinnamate anion (p-MeCA^?) in rigid organic glasses at 77 K. With a stretched-polymer-film technique, we assigned the resonance fields in the time-resolved EPR spectra of the lowest excited triplet (T₁) states ofp-MeCA andp-MeCA^?. From the analysis of these spectra we concluded that the deviation from planar structure in the T₁ state is small inp-MeCA andp-MeCA^? and the direction of C=O iss-cis to the ethylenic C=C bond inp-MeCA. The deprotonation appears to have little effect on the zero-field splitting (ZFS) parameters. The ZFS parameters were calculated theoretically using semiempirical molecular orbitals. The sublevel preferentially populated by intersystem crossing (ISC) is T _y in bothp-MeCA andp-MeCA^?. However, following the deprotonation ofp-MeCA, (P _y?P _z)/(P _x?P _z) changes from 5.7 inp-MeCA to 2.1 inp-MeCA^? (P _i are relative populating rates; thex andy axes are close to the long and short in-plane molecular axes, respectively, andz-axis is perpendicular to the molecular plane). The fluorescence lifetimes indicate that the deprotonation has little effect on the sum of the three ISC rate constants for the three T₁ sublevels. A decrease in acidity ofp-MeCA upon excitation has been observed.