Evolution of the modulated antiferromagnetic structure of CeAl2 in the presence of nonmagnetic impurities

Neutron diffraction studies show that the alloy system Ce_1-xLa_xAl₂ with x = 0.1 and 0.2 orders in the same incommensurate modulated antiferromagnetic structure as the pure compound CeAl₂. The existence and concentration dependence of a commensurate extra reflection ($\text{5}\text{2}$$\text{3}\text{2}$$\text{1}\text{2}$) is interpreted as being due to a modulation quenching of the CeAl₂ structure. This is in contrast to the suggestion that the magnetic order of CeAl₂ can be described by a triple-q structure.     

Spin dynamics in the impurity-doped one-dimensional heisenberg paramagnet (CH3)4NMn(1-x)CuXCl3: Nuclear magnetic relaxation

Proton spin-lattice relaxation rate has been measured at room temperature in the impurity-doped (CH₃)₄NMn_(1-x)Cu_xCl₃ for X = 0.04, 0.1 and 0.17. The result for Hz. snfc;chain-axis as a function of resonance frequency clearly shows that the spectral density of the spin fluctuations in the impure system remains to have the characteristics 1-D diffusive term (ω^{-$\text{1}\text{2}$}), with a slower rate of the spin diffusion in accordance with the theory by Richards. The result for H⊥ chain-axis indicates, however, the existence of a singularity of the fluctuations near ω = 0.     

Far infrared studies of lattice and free carrier effects in Hg1-xMnxTe

The far infrared reflectivity of Hg_1-xMn_xTe samples with x = 0.01, 0.06, and 0.11 has been measured between 5.5 and 295 K. For x = 0.06 and T = 5.5 K, fits to a dielectric function including an approximate interband term gave the first determination of $\text{m}{}^1\text{/m}{}_0\text{= 0.0059}$, and band gap value, -39±10 meV, in good agreement with the result of Bastard et al. The temperature and alloy dependence of the coupled plasmon-phonon modes has also been determined.     

Thermochemical analysis of PdxAg1-x alloys from XPS core-level binding energy shifts

XPS core level binding energy shifts of the $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ energy levels of Pd and Ag for a large number of coevaporated Pd_xAg_1-x alloys with 0?x?1 have been measured. An analysis of the Pd level shifts yields the heats of formation of the PdAg alloy system in good agreement with those reported from calorimetric measurements. Combining these data with the Ag level shifts one obtains the heat of formation of Cd diluted into Pd_xAg_1-x.     

Study of isovector charge-exchange excitations and their decay via the 16O(3He,tp) reaction

The nucleus ¹⁶F was studied via the ¹⁶O(³He, t) reaction at 81 MeV. Differential cross sections for many states were obtained and interpreted with DWBA calculations, using microscopic wave functions and an effective projectile-nucleon interaction. Proton decay to several states in ¹⁵O was observed and angular correlations for protons in coincidence with tritons detected at θ = 0° were measured. Several spin-parity assignments have been made. The distribution of isovector ΔL = 1 strength could be deduced. The analog of the giant dipole resonance ($\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{? 9.5}\text{MeV}\text{)}$ is strongly excited. The magnetic quadrupole strength has two strong components, one low, at E_x = 0.424 MeV, and one high, at $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{? 7.5}\text{MeV}$. Evidence is given for a proportionality between cross section and M2 strength for transitions to J^π = 2^? states, which possibly make the (³He, t) reaction a suitable tool for determining quantitatively isovector M2 (or B_ij) strengths.     

Angular distributions and structure functions from two-jet events at the CERN SPS pp collider

The two-jet cross section measured in the UA1 apparatus at the CERN $\text{p}\text{p}$ Collider has been analysed in terms of the centre-of-mass scattering angle θ and the scaled longitudinal parton momenta x₁ and x₂. The angular distribution dσ/d cos σ rises rapidly as cos → 1, independent of x₂ and x₂, as expected in vector gluon theories (QCD). The differential cross section in x₁ and x₂ is consistent with factorization and provides a measurement of the proton structure function $\text{F(x) = G(x) +}\text{4}\text{9}\text{[Q(x) +}\text{Q}\text{(x)]}$ at values of the four-momentum transfer squared, -t? ≈ 2000 GeV². Over the range x = 0.10?0.80 the structure function shows an exponential x dependence and may be parametrized by the form F(x) = 6.2 exp (?9.5x).     

Hyperfine and nuclear quadrupole interactions in copper-doped cadmium oxalate trihydrate single crystals

Electron spin resonance experiments on Cu²⁺ doped in a single crystal of cadmium oxalate trihydrate grown by a slow diffusion technique have been carried out at 77 K. The major features of the ESR spectra can be attributed to divalent copper (3d⁹) in substitutional Cd²⁺ sites. Information has been gained about the hyperfine and quadrupole interactions concerning the ion. The spin-Hamiltonian parameters in the $\text{S =}\text{1}\text{2}$, $\text{I =}\text{3}\text{2}$ manifold are: g_x = 2.0211; g_y = 2.2249; g_z = 2.4536; A_x = +84.5 × 10^?4cm^?1; A_y = +16.8 × 10^?4cm^?1; $\text{A}{}_{\mathrm{z}}\text{= ?40.8 × 10 ×}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$; P_x = ?7.4 × 10^?4cm^?1; P_y = ?0.4 × 10^?4cm^?1; and P_z = +7.8 × 10^?4cm^?1. An evaluation of the asymmetry and quadrupole coupling parameters revealed that the ground state of the guest ion in Cd(COO)₂ · 3H₂O is 0.97|x² ?y₂ > +0.24 |3z² ? r² >.     

A thermodynamic study of nonstoichiometric cerium dioxide

Thermogravimetric measurements were performed on nonstoichiometric CeO_2?x in the temperature range 750–1500°C and from oxygen pressures of 10^?2 to 10^?26 atm. From this data the deviation from stoichiometry x = x(T, P_o2) was determined. The thermodynamic quantities Δ$\text{H}$_o2 and Δ$\text{S}$_o2 were calculated in the region 0.001? x ? 0.3 and found to be independent of temperature.In the composition region 0.001< x < 0.006, the variation of Δ$\text{S}$_o2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δ$\text{H}$_o2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δ$\text{H}$_o2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed.In the composition region 0.006 < x < 0.1, x ∝ with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ with n increasing rapidly with x to n? 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO_1·72 and CeO_1·70 was not observed in this study at temperatures between 1300° and 1500°C.     

Formation and lithuim ionic conduction of the antifluorite type solid electrolytes,Li2+x-y-z[(NH)1-x-y-zNxClyHz]

Antifluorite type solid electrolytes, Li_2+x-y-z[(NH)_1-x-y-zN_xCl_yH_z] have been synthesized from Li₃N, LiCl and LiCl·H₂O or $\text{Li}{}_2\text{[(}\text{NH}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{H}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$]. Either of the last two compounds introduces NH^2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH^2- ions in the compound, reflecting the difference of anion sizes between Cl^- and NH^2- ions. Activation energies of Li⁺ diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH^2- ions, although the values differ by a factor of ≈2 netween the both methods.     

Measurement of the electric quadrupole moment of the 482 keV state of 181Ta by the time differential perturbed angular correlation technique

The electric quadrupole interaction of the 482 keV state of ¹⁸¹Ta in an environment of metallic rhenium has been investigated by time differential angular correlation measurements. For the field gradient calibration a recent observation^{1, 2}) of the quadrupole splitting of the 6.3 keV line of ¹⁸¹Tain the same environment has been used. Adopting the quadrupole moment of the ground state which was derived from muonic X-ray data ³) we obtain $\text{Q}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{(482}\text{keV}\text{) = 2.51 ± 0.15}\text{b}$. A comparison of the intrinsic quadrupole moment Q₀ with that of the ground state revealed that the excited state is slightly less deformed: $\text{Q}{}_0\text{(}\text{5}\text{2}{}^{\mathrm{+}}\text{)/Q}{}_0\text{(}\text{7}\text{2}{}^{\mathrm{+}}\text{) = 0.936 ± 0.014}$. A measurement of the temperature dependence between liquid nitrogen and room temperature showed that the electric quadrupole interaction remains essentially constant.     

Equilibrium of three liquid phases and approach to the tricritical point in benzene-ethanol-water-ammonium sulfate mixtures

We have determined the region of coexistence of three liquid phases in the system C₆H₆-EtOH-H₂O-(NH₄)₂SO₄ at 21°, 45°, 48° and 48.6°C, and have located the tricritical point. The temperature and composition at the tricritical point are T_t = 48.9°C and mass fractions x_salt = 0.0175, x_water = 0.351, x_ethanol = 0.450, x_benzene = 0.181. This composition is inferred to lie outside the three-phase region at 21° and 45°, in agreement with the phenomenological theory of Griffiths. The locus of the three liquid phases in the isothermal composition tetrahedron has the parabolic, inflected (cubic), and cusped aspects predicted by the theory. For the three exponents β₁, β₂, and β₃ associated with the vanishing of the three characteristic dimensions of the coexistence region, we find β₁ = 0.4, β₂ = 1.0, β₃ = 1.5, compared to the theoretical $\text{β}{}_1\text{=}\text{1}\text{2}\text{, β}{}_2\text{= 1, β}{}_3\text{=}\text{3}\text{2}$. We verify that the algebraic degree 1/β′ of the coexistence curve near the two critical end points exceeds its classical value of 2.     

High-temperature superconductivity in the BaPb1-xBixO3 systems

Phases of the type BaPb_1-xBi_xO₃ have been prepared for the first time. These phases all have perovskite related structures, and superconductivity was observed over the range $\text{x ≌ 0.05-0.3}$. The highest critical temperature is 13 K which is exceptionally high for an oxide and is much higher than that previously observed for any superconductor not containing a transition element. Semiconducting behavior is observed from x = 1 to about 0.35.     

Diffusion et rotation du fluor dans un fluorure ionique: etude par R.M.N. de Ba4−xZr2 + x2F16

Fluoride subcell thermal behavior has been studied from 180 to 450 K for two compositions Ba_4?xZr_{2 + $\text{x}\text{2}$}F₁₆ corresponding to x = 0.04 and x = 0.26. At low temperature two fluorine atoms rotate quickly around a baryum atom. Above 330 K this phenomenon leads diffusion thanks to an exchange mechanism between the previous fluorine atoms and the others, the whole anipnic subcell being then affected by the fluorine mobility. Activation energy decreases from 0.52 to 0.46 eV as x increases from 0.04 to 0.22. This property seems to be closely related to the formation of cationic vacancies whose number increases with x.     

Conductivite ionique des systemes Kx(Znx/2Ge1-x/2)O2 et Kx(GaxGe1-x)O2 de structure cristobalite

The crystal chemistry of the K_x(Zn_x/2Ge_{1-$\text{x}\text{2}$})O₂ and K_x(Ga_xGe_1-x)O₂ systems has been investigated. In each of them a solid solution with a cristobalite-type structure has been obtained with a 0.90?×?1 range. The K⁺ conductivity increases strongly with vacancy content, while the activation energy remains nearly constant.Influence of various crystal chemical parameters on the conductivity (lattice covalency, size of the bottlenecks, etc...) is discussed.     

Rotational spectrum of sulfuryl bromide fluoride

The rotational spectra of SO₂⁷⁹BrF and SO₂⁸¹BrF have been obtained between 18 and 40 GHz. Both molecules are near-prolate symmetric rotors with a and b-type dipole components. A least-squares fit of the observed moments of inertia obtained by correcting for the bromine quadrupole interaction yields $\text{r}\text{(SBr) = 2.155 ± 0.006}\text{A}\text{?}$ and ? FSBr=100.6°±1.5° structural parameters when $\text{r}\text{(SO) = 1.407}\text{A}\text{?}$, $\text{r}\text{(SF) = 1.56}\text{A}\text{?}$, and ? OSO=123.7° are assumed.     

Microwave spectrum of ethyl iodide: Nuclear quadrupole interaction and centrifugal distortion analysis

The microwave spectrum of ethyl iodide has been reinvestigated between 4 and 80 GHz. A total of 181 ground-state transitions with J ≤ 26 and $\text{F ≤}\text{57}\text{2}$ have been analyzed using numerical diagonalization of the quadrupole Hamiltonian. The following rotational and quadrupole coupling constants have been determined (in MHz): A′ = 29 116.321; B′ = 2979.5639; C′ = 2796.4520; χ_aa = ?1478.111; χ_bb = 564.464; χ_cc = 913.648, and χ_ab = 896.38. The quadrupole coupling constants have been transformed to their principal axis system. All the quartic centrifugal distortion constants have been significantly determined, the standard deviation of the fit being only σ = 31 kHz.     

Ionic-electronic conductors based on lithium-containing oxide bronzes

Lithium-containing oxide bronzes Li_xV_2?yM_yO₅-β (M=Mo or W) have been studied in wide range of temperature (25–550°C) and composition (0.22?x?0.47, 0?y?0.25) as prospective ionic-electronic conductors. By coulometric titration tecknique, $\text{Δ}\text{G}{}_{\mathrm{<mtext>Li</mtext>}}$, $\text{Δ}\text{H}{}_{\mathrm{<mtext>Li</mtext>}}$ and $\text{Δ}\text{S}{}_{\mathrm{<mtext>Li</mtext>}}$ have been found and ordering of the lithium ions within the channel structure Li_xV₂O₅-β has been discussed depending on composition and temperature. The chemical diffusion coefficient for lithium D?_Li has been measured by potentiometric technique on hot-pressed ceramic samples. The lithium self-diffusion coefficient D_Li and partial lithium-ionic conductivity have been calculated.     

Analysis of the (ν1 + ν2) and (ν2 + ν3) combination bands of ozone

The fine structures of the (ν₁ + ν₂) and (ν₂ + ν₃) combination bands of ozone in the 5.7-μm region have been recorded and analyzed. The two vibrational states are coupled through Coriolis and second-order distortion terms. The interaction has been treated by the numerical diagonalization of the secular determinant for the two coupled states. With the centrifugal distortion parameters fixed to the ground state values, the following constants have been obtained: ν₁ + ν₂ = 1796.26₆, A₁₁₀ = 3.610₄, B₁₁₀ = 0.4414₅, $\text{C}{}^1{}_{110}\text{= 0.3902}{}_9$, ν₂ + ν₃ = 1726.52₆, A₀₁₁ = 3.553₇, B₀₁₁ = 0.4398₂, $\text{C}{}^1{}_{011}\text{= 0.3884}{}_4$, Y₁₃ = ?0.46₆, and X₁₃ = ?0.01₀ cm^?1. In addition, the following anharmonic constants have been obtained: x₁₂ = ?7.82₁ and x₂₃ = ?16.49₄ cm^?1. The value of the dipole moment ratio, $\text{R =}\text{〈011|μ}{}_{\mathrm{z}}\text{|0〉}\text{〈110|μ}{}_{\mathrm{x}}\text{|0〉}$, is 1.30 ± 0.10.     

The effect of the next nearest neighbor ion on the X-ray photoelectron spectra of 2p levels for Co2+, Ni2+ and Cu2+ in MgO

The X-ray photoelectron spectra of Co, Ni and Cu 2p levels for samples of M_xMg_1-xO (M = Co, Ni, Cu), CoO, NiO and CuO were compared. The binding energies of metal 2p_{$\text{3}\text{2}$} levels did not change with their concentration. The shake-up satellite main peak intensity ratios and FWHM of metal 2p levels for Co²⁺ and Cu²⁺ in MgO were smaller than those for CoO and CuO. The Ni 2p_{$\text{3}\text{2}$} spectrum for Ni²⁺ in MgO had no shoulder, unlike NiO. Results indicate that next nearest neighbor ions (metal ions) may influence the final states after photoelectron ejection.     

A new representation for the density matrix: (II). Equations of motion

The equations of motion for the new SU(n) parameters representing the density matrix for arbitrary spin are derived. It is shown that for a class of hamiltonians which are diagonal, the equations are exactly solvable by using the device of combining the SU(n) parameters in pairs using the Pauli spin matrix σ_y. It is also shown that using the correspondence relations between the SU(n) parameters and the spherical tensor moments, it is possible to picture the time evolution of the tensor parameters using the explicit solutions for the SU(n) parameters. This procedure has been illustrated by discussing in detail the problem of spin-1 and $\text{spin}\text{-}\text{3}\text{2}$ systems interacting with an external magnetic field and subjected to quadrupole interactions.