Conductivity anisotropy in directionally solidified CaZrO3---CaSZ and MgO-MgSZ eutectics

The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO₃---ZrO₂(cubic) and MgO---ZrO₂(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO₃-ZrO₂(cubic) and fibers of MgO in a ZrO₂ matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO₃---ZrO₂ the coductivity is clearly anisotropic. The following values for σT have been obtained: the conductivity at 600 °C equals 2.0 × 10⁻⁶ Ω⁻¹ cm⁻¹ perpendicular to the fiber axis and 1.4 × 10⁻⁵ Ω⁻¹ cm⁻¹ parallel to it and with an activation energy of 1.3 eV for σT. For MgO---ZrO₂(cubic) the isotropic value of the conductivity at 600 °C is 10⁻⁴ Ω⁻¹ cm⁻¹ with activation energy for σT of 1.5 eV. The anisotropic conductivity in the CaZrO₃---ZrO₂ (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO₂) and non-conducting (CaZrO₃ or MgO) phases.     

Fluctuations in a supersymmetric inflationary universe

It has been demonstrated that fluctuations in the new inflationary universe may be almost scale-invariant, but are unfortunately too large. We show that supersymmetric inflationary models allow the fluctuations to be smaller. In a toy supersymmetric model, the perturbations are O(10⁻⁴) is the Yukawa interactions are O(10⁻⁶μ/m_p) where μ is the magnitude of the Higgs vacuum expectation value driving the inflation. It is therefore easier to have small fluctuations if inflation occurs close to the Planck epoch.     

Diffusion of W on A W(211) plane

The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D₀ = (3 ± 1) × 10⁻⁵ cm² s⁻¹. For diffusion across channels E =6.6 kcal, D₀ = 4 × 10⁻⁹cm² s⁻¹ at T < 752 K, and E = 24 kcal, D₀ = 5 × 10⁻⁴ cm² s⁻¹ at T > 752 K. The results for diffusion along channels yield E and D₀ values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy (E = 19 kcal, D₀ = 7.7 × 10⁻³ cm² s⁻¹) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit (E = 13.3 kcal, D₀ = 7 × 10⁻⁷ cm² s⁻¹). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D₀ above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed.     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

The study of hydronium NASICON conductivity with deuterium

The ionic conductivity of the bulk phase of bonded hydronium NASICON (Hyceram^TM) was measured at equilibrium with an H₂O/N₂ and then a D₂O/N₂ atmosphere, each at 100% relative humidity and 75% relative humidity over the temperature range 25°C to 50°C. At 100% relative humidity and 25°C, the protonic system had a bulk conductivity of 5.0×10⁻⁴ S/cm and an activation energy of 17.3kJ/mole; the same sample, when deuterated, had a bulk conductivity of 2.2×10⁻⁴ S/cm and an activation energy of 19.3kJ/mole. At 75% relative humidity and 25°C, the conductivity of the protonated system decreased to 1.4×10⁻⁴S/cm with an activation energy of 24.1 kJ/mole. The deuterated sample at 75% relative humidity had a bulk conductivity of 5.4×10⁻⁵ S/cm with an activation energy of 26.0 kJ/mole. The isotope effect suggested a proton hopping (Grotthus) mechanism as the means by which the protons pass through the lattice.     

A new measurement of the weak magnetism term in the betaspectra of B and N

The betaspectra of ¹²B and ¹²N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW² and b₋ = 1.106 × 10⁻⁴ MeV⁻², b₊ = −1.397 × 10⁻⁴ MeV⁻², the spectra yield a₋ = (+0.91 ± 0.11) × 10⁻² MeV⁻¹ and a₊ = (−0.07 ± 0.09) × 10⁻² MeV⁻. the a₋ − a₊ = (+0.98 ± 0.09) × 10⁻² MeV⁻¹ is in agreement with the weak magnetism prediction.     

Lithium scandium phosphate-based electrolytes for solid state lithium rechargeable microbatteries

Li₃Sc₂(PO₄)₃ is a promising candidate for use as an electrolyte in solid state lithium rechargeable microbatteries due to its stability in air, ease of preparation, and resistance to dielectric breakdown. The room temperature ionic conductivity was optimized resulting in an increase of over two orders of magnitude to 3×10⁻⁶S/cm. The formation of Li₃(Sc_2−xM_x)(PO₄)₃, where M=Al³⁺ or Y³⁺, resulted in the decrease of porosity, greater sinterability, and considerable enhancement of the ionic conductivity. Yttrium substitutions enhanced the conductivity slightly while aluminum increased the room temperature ionic conductivity to 1.5×10⁻⁵S/cm for x=0.4. Preliminary electron beam evaporation of Li₃Sc₂(PO₄)₃ yielded amorphous thin films with ion ic conductivity as high as 5×10⁻⁵S/cm and a composition of Li_4.8Sc_1.4(PO₄)₃.     

Electron stimulated desorption of CO from Pd1/W(110)

The electron impact behavior of CO adsorbed on Pd₁/W(110) was investigated. The desorption products observed were neutral CO, CO⁺, and O⁺. After massive electron impact residual carbon, C/W = 0.15, but not oxygen was also found, suggesting that energetic neutral O, not detected in a mass analyzer must also have been formed. Formation of β-CO, i.e., dissociated CO with C and O on the surface was not seen. The total disappearance cross section varies only slightly with coverage, ranging from 9 × 10 ⁻¹⁸ cm² at low to 5 × 10⁻¹⁸ cm² at saturation (CO/W = 0.75). The cross section for CO⁺ formation varies from 4 × 10⁻²² cm² at satura to 2 × 10⁻²¹ cm² at low coverage. That for O⁺ formation is 1.4 × 10⁻²² cm² at saturation and 2 × 10⁻²¹ cm² Threshold energies are similar to those found previously [J.C. Lin and R. Gomer, Surf. Sci. 218 (1989) 406] for CO/W(110) and CO/Cu₁/W(110) which suggests similar mechanisms for product formation, with the exception of β-CO on clean W(110). It is argued that the absence or presence of β-CO in ESD hinges on its formation or absence in thermal desorption, since electron impact is likely to present the surface with vibrationally and rotationally activated CO in all cases; β-CO formation only occurs on surfaces which can dissociate such CO. It was also found that ESD of CO led to a work function increase of the remaining Pd₁/W(110) surface of 500 meV, which could be annealed out only at 900 K. This is attributed to surface roughness, caused by recoil momentum of energetic desorbing entities.     

From Planck to GUT via dimensional transmutation

Consider a gauge singlet superfield S coupled to a pair of adjoint fields in a SUSY-GUT. If the tree-level vacuum is flat in S, the vev S which defines the GUT scale will be determined via dimensional transmutation at a scale M where the soft-breaking (mass)² vanishes as a result of running from M_P = (8πG_N)^−1/2. Because of the large number of adjoint fields N_A coupled to S, one finds that M can be generically close to M_GUT = 2 × 10¹⁶GeV:

, where λ is a Yukawa 0.7. This work examines the symmetries and dynamical constraints required in a SUSY-GUT in order that the desired flatness in S is achieved, and that this flatness may survive in a supergravity framework.     

Investigation of parity mixing in Ta and Lu by measurement of the circular polarization of γ-rays

The circular polarization of the 482 keV γ-radiation of ¹⁸¹Ta and the 343 keV γ-radiation of ¹⁷⁵Lu was measured with a Compton polarimeter. Spurious effects arising from higher order contributions of quantum electrodynamics to the Compton scattering cross section were discovered. The results for the polarization are P = − (4.1±1.3)10⁻⁶ for ¹⁸¹Ta and P = − (1.5±6.0)10⁻⁶ for ¹⁷⁵Lu. These values are corrected for instrument asymmetries, bremsstrahlung and intensity of other lines.     

The role of Sb(5+) in the structure of Sb(2)O(3)-B(2)O(3) binary glasses--an NMR and Mössbauer spectroscopy study

Glasses of general formula xSb₂O₃ (1−x)B₂O₃ (0x0.8) have been prepared by conventional melt- quenching. Mössbauer spectroscopy shows that a fraction of the Sb³⁺ is converted to Sb⁵⁺ and this fraction increases with x. High-field ¹¹B MAS NMR gives well-resolved resonances from boron atoms which are 3- and 4-coordinated to oxygen. The fraction of 4-coordinated boron, N₄, goes through a maximum value of 0.12±0.01 at x=0.5. The position of the maximum in N₄ is consistent with the cation potential for Sb³⁺, as observed for other systems. However, the low value of N₄ at this maximum is not so readily explained. The values are similar to those predicted if [BO₄]⁻ were stabilised by [SbO₄]⁺ but the trends with composition are different.     

Preferential sputtering and radiation enhanced segregation in palladium-platinum alloys

Five palladium-platinum alloys of different compositions ranging from 10 to 90 at% Pd were sputtered with 1 keV Ar⁺ ions. The surface concentrations were then determined with Auger electron spectroscopy (AES) and low energy ion scattering spectroscopy (ISS). The observed concentrations differed largely from bulk values. This difference is explained in terms of the difference in sputtering yields for platinum and palladium and the radiation enhanced segregation of palladium. The surface was then mechanically cleaned in situ. The surface concentrations measured subsequently corresponded excellently with the bulk values confirming the calibration procedure for the calculation of the surface concentrations. A recently developed model for surface segregation was used to fit the experimental data. Values for the surface segregation energy ΔG and the radiation enhanced diffusion coefficient D were obtained in the range 2000–8000 J/mol and (1.2–8.0)×10⁻²⁰ m²/s, respectively.     

The deuteron A(Q) structure function and the neutron electric form factor

We have measured the deuteron A(Q²) structure function in the momentum transfer region between 1 and 18 fm⁻². The accuracy of the data ranges from 2 to 6%. These measurements allow a sensitive test of theoretical predictions. We find that meson-exchange currents and relativistic corrections significantly improve the agreement between experiment and theory. We investigate the sensitivity of A(Q²) to the nucleon-nucleon interaction and to the neutron electric form factor G_Eⁿ(Q²). Our analysis shows that G_Eⁿ(Q²) can be extracted from these data with a significantly improved accuracy. The model dependence of this analysis is discussed.     

Intensification of the peroxide macroradical formation in polytetrafluoroethylene under action of mixed (n,γ)-radiation in the vicinity of recoil atom tracks

Formation of peroxide macroradicals in PolyTetraFluoro Ethylene (PTFE) under γ-rays, protons (100 MeV), heavy Xe-ions (1 MeV/ nucleon), and mixed (n,γ)-irradiation has been investigated. An unusually high value of the macroradical formation yield in the case of reactor irradiation (G(R)_n,γ=(7.04±0.18)×10⁻² 1/100 eV) as well as unusual increase of G(R) in the first three cases with growing linear energy transfer (LET) values has been explained as an evidence for synergetic effects that may appear during radiation degradation of PTFE in the fields of mixed ionizing radiation.     

Polarisation circulaire du rayonnement gamma de Sb, Cs et Ag

The βγ circular polarization correlation of the 3⁻(β⁻ 621 keV)3⁻(γ 1692)2⁺ cascade in ¹²⁴Sb, the 4⁺(β⁻ 662)4⁺ (γ 796)2⁺ (γ 605)0⁺ in ^13Z4Cs and the 6⁺(β⁻529)6⁺ (γ 937)4⁺ (γ 885)2⁺ (γ 658)0⁺ in ^110mAg have been studied by using a Compton effect polarimeter. The measured asymmetry parameters are 0.172±0.004, −0.0702 ±0.0024 and 0.0549±0.0013 respectively.     

Davydov splitting and two-photon excitation of cadmium tungstate (CdWO4) single crystal phosphorescence

Phosphorescence characteristics of CdWO₄ excited by one-photon (λ = 308 nm) and two-photon (λ = 570–590 nm) processes were measured. A Davydov splitting of 120 ± 20 cm⁻¹ was obtained in the phosphorescence spectra, suggesting a diffusion coefficient of about 1.2 × 10⁻² cm² s⁻¹, and a diffusion length of about 3.1 × 10⁻⁴ cm for the room temperature measured lifetime of 8μs. The phosphorescence quantum efficiency was less than 2% at low temperatures (only 0.25% at room temperature), indicating that the dominant decay mechanism was radiationless. The radiative lifetime was thus estimated as 1–2 ms. The two-photon phosphorescence excitation is characterized by an absorption cross-section of the order of 10⁻⁴⁹cm⁴s.     

Prediction of low-lying oddballs in lattice QCD

We find, in a high precision Monte Carlo calculation of the glueball mass spectrum in pure SU(3) lattice gauge theory, a low-lying oddball with quantum numbers 1⁻⁺. We estimate its mass to be m(1⁻⁺)=1.68±0.18 GeV. We also measure the mass of the 0⁻⁻ oddball and find m(0⁻⁻)=2.79±0.22 GeV.     

Oxygen diffusion and surface exchange in La1−xSrxFe0.8Cr0.2O3−δ (x=0.2, 0.4 and 0.6)

Oxygen tracer diffusion (D*) and surface exchange rate constant (k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La_1−xSr_xFe_0.8Cr_0.2O_3−δ (x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10⁻²¹ atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV (x=0.2), 1.53 eV (x=0.4) and 1.21 eV (x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10⁻⁸ cm² s⁻¹ for x=0.2 to 10⁻⁷ cm² s⁻¹ for x=0.4 and 0.6. The activation energies determined at constant H₂O/H₂ ratio are 1.21 eV (x=0.2), 1.59 eV (x=0.4) and 0.82 eV (x=0.6).

The surface exchange rate constant of oxygen for the H₂O molecule is similar in magnitude to that for the O₂ molecule and both increase with increasing Sr concentration.     

LEED studies of the adsorption of CO2 on thin epitaxial NaCl(100) films

The adsorption of CO₂ on the NaCl(100) surface was studied with a high-resolution LEED-system. Measurements without charging up at low electron energies and without damage by the e-beam could be performed by using ultrathin epitaxial films on a conducting Ge(100) substrate. The adsorption behavior was recorded as a function of time and pressure at constant substrate temperatures of 78 and 83 K and CO₂ partial pressures from 4 × 10⁻⁸−2 × 10⁻³ Pa. The adsorption system shows a first-order two-dimensional phase transition to a (2 × 1) superstructure including glide planes (herringbone-like structure) at p = 7.2 × 10⁻⁸Pa (T = 78 K). The condensation of the CO₂ solid is starting at p = 1.5 × 10⁻⁴ Pa (T = 78 K). The LEED-pattern shows in this c(2 × 2) superstructure, which corresponds to the pyrite-like structure of the CO₂ solid. Both observed superstructures are commensurable with the NaCl(100) surface. Observation of island growth shows that the domains of the (2 × 1) superstructures have already at coverage of 5% of a monolayer an average lateral size of at least 200 A.     

Z-scan determination of the third-order optical nonlinearity of a triphenylmethane dye using 633 nm He–Ne laser

The third-order nonlinear optical response of a triphenylmethane dye (Acid blue 7) was studied using the Z-scan technique with a continuous-wave He–Ne laser radiation at 633 nm. The magnitude and sign of the third-order nonlinear refractive index n₂ of aqueous solution of Acid blue 7 dye were determined; the negative sign indicates a self-defocusing optical nonlinearity in the sample studied. The negative nonlinear refractive index n₂ and nonlinear absorption coefficient β were estimated to be −1.88 × 10⁻⁷ cm²/W and −3.08 × 10⁻³ cm/W, respectively, corresponding to Re(χ⁽³⁾) = −8.35 × 10⁻⁶ esu, and Im(χ⁽³⁾) = −6.88 × 10⁻⁷ esu. The experimental results show that Acid blue 7 dye have potential applications in nonlinear optics.