Reversible H2 passivation of Si ≡ Si3 interface defects in (1 1 1)Si/SiO2

K-band electron spin resonance (ESR) at 4.3 K has revealed the dipole-dipole (DD) interaction effects between [1 1 1]P_b centers (^*Si ≡ Si₃ defects with unpaired sp³ hybrid [1 1 1]) at the 2 dimensional (1 1 1)Si/SiO₂ interface. This has been enabled by the perfectly reversible H₂ passivation of P_b, which affects the defect's spin state. Sequential hydrogenation at 253–353°C and degassing treatments in high vacuum at 743–835°C allowed to vary the P_b density in the range 5 × 10¹⁰ < [P_b] (1.14 ± 0.06) × 10¹³ cm^-2. With increasing [P_b] fine structure doublets are clearly resolved. It is found that (1 1 1)Si/SiO₂ interfaces, dry thermally grown at ≈920°C, naturally comprise a ^*Si ≡ Si₃ defect density — passivated or not — of 1.14 × 10¹³ cm^-2.     

Tuning the multiferroic properties of Pb(Fe1/2Nb1/2)O3 by cationic substitution

A series of substituted lead iron niobate compounds with the general formula Pb²⁺_(1−x)A^Z_x(Fe_{{(1−(2−Z)x)/2}}Nb_{{(1+(2−Z)x)/2}})O₃ (0<x<0.6 and A=La³⁺, K⁺ or Sr²⁺) were prepared by a modified solid-state synthesis. The relative concentrations of Fe³⁺ and Nb⁵⁺ were adjusted to compensate the charge imbalance due to the aliovalent substitution. The dielectric constant and magnetic susceptibilities were studied as a function of temperature. The temperature of the dielectric maximum, T_M, of the substituted compounds decreased linearly with increasing concentration of the substituent ions. The magnetic measurements showed an antiferromagnetic transition at temperatures T_N1 due to the superexchange interactions mediated by Fe–O–Fe and an additional antiferromagnetic-type transition at T_N2. T_N1 linearly increased with the increasing concentration of Fe³⁺ ion at the B-site of ABO₃-type substituted compounds. T_M is shown to be directly dependent on the concentration of the ferroactive Nb⁵⁺ ions at the B-site and Pb²⁺ ions at the A-site.     

Ionic conductivity of crystalline and glassy Mg4.5Na7(P2O7)4

In our work single crystals of Mg_4.5Na₇(P₂O₇)₄ were prepared, pulverized, pressed into pellets and sintered in order to measure the electrical conductivity of polycrystalline specimens. The conductivity was also measured on glassy specimens obtained by the melting of previously prepared crystals. The electrical conductivities at 25°C with values of the order of 10⁻¹⁶ Ω⁻¹ cm⁻¹ for polycrystalline samples and a value of the order of 10⁻¹⁴ Ω⁻¹ cm⁻¹ for glass, show that the glassy phase of Mg_4.5Na₇(P₂ because of its greater molar volume and loosely packed structure, is a better matrix for ionic motion.     

Determination of different oxygen transport mechanisms and measurement of the oxygen ion conductivity of Y1Ba2Cu3O7−x

By undertaking AC electrochemical impedance experiments on yttria stabilised zirconia electrolytes with polished Y₁Ba₂Cu₃O_7−x electrodes, the activation energy for oxygen ion transport within the bulk of Y₁Ba₂Cu₃O_7−x, in air, over the temperature range 823 K–1043 K, was determined to be 1.50 ± 0.05 eV. At 1000 K the oxygen ionic conductivity was calculated to be around one order of magnitude lower than that in yttria stabilised zirconia. Typical calculated values were σ=5×10⁻⁵ (ω cm)⁻¹ and 6×10⁻³ (ω cm)⁻¹ at the respective temperatures 823 K and 1043 K. By employing a similar cell but with Y₁Ba₂Cu₃O_7−x paste electrodes, oxygen transfer between the Y₁Ba₂Cu₃O_7−x and the electrolyte was found to occur via a surface diffusional processes. Over the temperature range 873 K–1098 K, in air, the activation energy for in-diffusion at the surface was found to be 1.4±0.1 eV and that for out-diffusion at the surface to be 1.76±0.05 eV.     

Magnetic anisotropy in the paramagnetic phase of TbAl2

The magnetic anisotropy of a single crystal of TbAl₂ has been measured by torque magnetometry from below the Curie point up to 170 K, well into the paramagnetic phase. Within a (110) plane the torque can be described by the expression L(θ) = {P sin 2θ} H² + {Q sin 2θ + S sin 4θ} H⁴ + {T sin 4θ} H⁶, where θ is the an gle formed by the magnetization vector with a [001] axis. The first term (in H²) is interpreted as produced by arrays of defects with axial symmetry. The second (in H⁴) and third (in H⁶) terms arise from anisotropic fourth and sixth rank tensor paramagnetic susceptibilities. On the other hand if the anisotropy is described in terms of effective conventional anisotropy constants K₁ and K₂ within the temperature range 90–170 K it is found that both constants change continuously across the Curie temperature and furthermore the [111] direction remains the easy direction in the paramagnetic range. Anisotropy measurements reveal themselves as a sensitive indicator of the level of macroscopic defects in magnetic crystals.     

Spectral intensities in the ν1 band of NH3

Intensities have been measured for individual transitions in the Q and R branches of the ν₁ band of NH₃ using a difference-frequency laser spectrometer. The data yield an integrated band strength of S⁰_v=219.36±1.03 cm^-2/MPa at 297 K, corresponding to a transition moment of μ_v = 8.535(20) × 10^-32 C·m, and a Herman-Wallis correction factor, (1 + _jm)², where _j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν₄ (E, L = 2), so were excluded from the fit. A small sample of ν₃ band lines occurring in the ν₁ band scans also yields a rough estimate of the ν₃ band intensity with evident irregular perturbations.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Phase transitions and electrical properties of CsH(SO4)0.76(SeO4)0.24 mixed crystals

The study by X-ray diffraction, calorimetry, vibrational and impedance spectroscopy of CsH(SO₄)_0.76(SeO₄)_0.24 new solid solution is presented. Crystals of this composition undergo two phase transitions at T = 333 and 408 K. The last one at 408 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O₄⁻] reorientation and fast H⁺ diffusion. A sudden jump in the conductivity plot confirms the presence of this transition. Above 408 K, this high temperature phase is characterized by high electrical conductivity (7 × 10^t-3 Ω⁻ cm⁻¹) and low activation energy (E_a < 0.3 eV).     

Cl nuclear quadrupole resonance studies of molecular motions of ClO3 and water diffusion in Ca(ClO3)2·2H2O

A ³⁵Cl nuclear quadrupole resonance (³⁵Cl-NQR) investigation of polycrystalline Ca(ClO₃)₂·2H₂O is described. The ³⁵Cl-NQR frequencies (ν_Q) for two resonance lines (ν_Q1 and ν_Q2), the spin lattice relaxation time (T_1Q) for ν_Q2 only and the line width δν_Q2 were measured in the temperature range 292–345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO₃⁻ ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T_1Q proved the occurrence of water diffusion and hindered rotation of ClO₃⁻ ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width δν_Q2 confirmed the conclusions drawn from the analysis of T_1Q(T).     

Structure determination, magnetic and optical properties of a new chromium(II) thioantimonate, [Cr((NH2CH2CH2)3N)]Sb4S7

The chromium(II) antimony(III) sulphide, [Cr((NH₂CH₂CH₂)₃N)]Sb₄S₇, was synthesised under solvothermal conditions from the reaction of Sb₂S₃, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P2₁/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS₃³⁻ trigonal pyramids and Sb₃S₆³⁻ semi-cubes generate Sb₄S₇²⁻ chains which are directly bonded to Cr(tren)²⁺ pendant units. The effective magnetic moment of 4.94(6)μ_B shows a negligible orbital contribution, in agreement with expectations for Cr(II):d⁴ in a ⁵A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides.     

Duree de vie et depolarisation par collisions avec l''helium des niveaux 5P3/2 Et 5P1/2 de l''ion Cd

The lifetimes of the Cd⁺ 5²P_3/2 and 5²P_1/2 states have been measured by the Hanle effect. The Cd⁺ ions are produced in a d.c. discharge in cadmium vapor, with helium as buffer gas. The results are: τ(5²P_3/2) = (2.60±0.20) ×10⁻⁹sec, and τ(5²P_1/2) = (3.05 ± 0.13) × 10⁻⁹sec.

We measured also the cross sections for the destruction of the orientation in the 5²P_1/2Cd⁺ state (<5Ų), of the orientation (18±10Ų) and of the alignment (46±10Ų) in the 5²P_3/2 state due to collisions with the helium atoms.     

Microwave studies of the superconducting state in Rb3C60

Methods of electron-spin resonance (ESR) and direct, non-linear field-modulated microwave absorption (FMMA) were applied for the measurements in low- and high-purity samples of rubidium-doped fullerene, Rb₃C₆₀. The coexistence of the normal strong ESR signals and regular series of weak absorption lines similar to those seen in systems of Josephson junctions was observed in the high-purity sample. The possible influence of the vortex lattice on the ESR signals was also studied. We determined from FMMA investigations using the Portis model the critical field μ₀H^* = 40 μT, the depinning current density J_c^*(μ₀H₀ = 1 mT) 4 × 10⁸ A/m² in low magnetic field and J_c^*(μ₀H₀ > 100 mT) 1.6 × 10⁸ A/m² in higher fields. These values were generally one order of magnitude higher than the highest corresponding values previously observed in high-temperature superconductors (HTS's).     

TEA-CO2 laser generation of ultrasound in non-metals

An industrial TEA-CO₂ laser, operating at a wavelength of 10.6 μm, has been used to produced broadband ultrasonic pulses in polymers. The generation mechanism falls into three categories. At low power densities ≤ 10⁷ W cm⁻² a thermoelastic regime predominates. As the power density is increased in the range (1–5) × 10⁷ W cm⁻² ablation of the material surface plays an increasingly important role in the acoustic generation. Thirdly, at greater power densities, plasma breakdown just above the material surface serves as the means of generation. This paper describes the acoustic sources for these types of generation mechanism and presents theoretically calculated acoustic waveforms to match those recorded experimentally.     

Dielectric and ferroelectric properties of the mixed crystals system (CH3NH3)5Bi2(1 − x)Sb2xCl11

Dielectric and pyroelectric properties of the mixed crystals system, (CH₃NH₃)₅Bi_{2(1 − x)}Sb_2xCl₁₁ (0 < x < 0.25) were systematically investigated. Temperature dependencies of ′_c in the vicinity of ferro-paraelectric phase transition were measured for the mixed crystals with x = 0.05, 0.07, 0.11, 0.13 and 0.25 in the frequency region 1 kHz–1 MHz. The substitution of bismuth atoms by antimony drastically reduces the magnitude of ′_c and shifts the ferro-paraelectric phase transition towards higher temperatures. The dielectric dispersion of the complex electric permittivity, _c^*, in x = 0.05 crystals was studied in the frequency range from 30 to 1000 MHz. Around 321 K phase transition, two dielectric relaxators are postulated; a low-frequency one in the megahertz region showing a critical slowing down and a high-frequency one in the gigahertz region.     

Infrared optical response of YBa2Cu3O7 and PrBa2Cu3O7 An ellipsometric study

Ellipsometry was used to study (110) and (001) oriented films of YBa₂Cu₃O₇ and PrBa₂Cu₃O₇ in the mid-and near-infrared spectral regions. Below a photon energy of 0.1 eV, the in-plane component of the dielectric tensor of YBa₂Cu₃O₇ is dominated by a Drude term with a squared plasma energy of (3.0 ± 0.3) eV². This “oscillator strength”, and the Lorentzian broadening energy of (0.104 ± 0.005) eV at room temperature, are confirmed by the changes induced in Pr-substituted material, and by low-temperature measurements in the near-infrared. The deviation from the Drude behavior observed above 0.1 eV is accounted for by a broad absorption band with an oscillator strength of (3.6 ± 0.1) eV² in YBa₂Cu₃O₇ which shifts to higher energies and takes over almost all of the oscillator strength of the Drude term when Y is substituted by Pr. The response to electric fields perpendicular to the planes is much weaker, with an upper bound of 0.63 eV² for the squared plasma energy. The in-plane loss function computed from the measured dielectric function follows the Drude-like lineshape, modified by the bound-state absorption band, down to the lowest energy reached in our measurements (0.058 eV).     

Studies of lithium intercalation in 3R-WS2

The lithium intercalation into the layered dichalcogenide 3R-WS₂ has been investigated by electrochemical reduction and by chemical reaction in n-butyl lithium solution. Essential results are (a) a charge transfer of nearly 0.6e⁻/W in Li_xWS₂, (b) a small increase of the c-axis parameter of about 0.6%, and (c) a high mobility of the Li⁺-ions. The chemical diffusion coefficient of Li⁺-ions is estimated to be 8 × 10⁻⁹ cm² s⁻¹ in the composition range 0 ≤ x ≤ 0.25. The appearance of a structural transformation from 3R-WS₂ to 2H-Li_xWS₂ is interpreted on grounds of instabilities in the interlayer structure.     

Material design of new lithium ionic conductor, thio-LISICON, in the Li2S–P2S5 system

A new lithium ionic conductor of the thio-LISICON (LIthium SuperIonic CONductor) family was found in the binary Li₂S–P₂S₅ system; the new solid solution with the composition range 0.0≤x≤0.27 in Li_3+5xP_1−xS₄ was synthesized at 700 °C and characterized by X-ray diffraction measurements. Its electrical and electrochemical properties were studied by ac impedance and cyclic voltammetry measurements, respectively. The solid solution member at x=0.065 in Li_3+5xP_1−xS₄ showed the highest conductivity value of 1.5×10⁻⁴ S cm⁻¹ at 27 °C with negligible electronic conductivity and the activation energy of 22 kJ mol⁻¹ which is characteristic of high ionic conduction state. The extra lithium ions in Li₃PS₄ created by partial substitution of P⁵⁺ for Li⁺ led to the large increase in ionic conductivity. In the solid solution range examined, the minimum conductivity was obtained for the compositions, Li₃PS₄ (x=0.0 in Li_3+5xP_1−xS₄) and Li₄P_0.8S₄ (x=0.2 in Li_3+5xP_1−xS₄); this conductivity behavior is similar to other thio-LISICON family with the general formula, Li_xM_1−yM_y′S₄ (M=Si, Ge, and M′=P, Al, Zn, Ga, Sb). Conduction mechanism and the material design concepts are discussed based on the conduction behavior and the structure considerations.     

Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study

Impedance spectroscopy was used to study the oxygen reaction kinetics of La_0.8Sr_0.2MnO₃ (LSM)-based electrodes on Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes. Three types of electrodes were studied: pure LSM, LSM–YSZ composites, and LSM/LSM–YSZ bilayers. The electrodes were formed by spin coating and sintering on single-crystal YSZ substrates. Measurements were taken at temperatures ranging from 550 to 850°C and oxygen partial pressures from 1×10⁻³ to 1 atm. An arc whose resistance R_el had a high activation energy, E_a=1.61±0.05 eV, and a weak oxygen partial pressure dependence, (P_O2)^−1/6, was observed for the LSM electrodes. A similar arc was observed for LSM–YSZ electrodes, where R_el(P_O2)^−0.29 and the activation energy was 1.49±0.02 eV. The combination of a high activation energy and a weak P_O2 dependence was attributed to oxygen dissociation and adsorption rate-limiting steps for both types of electrodes. LSM–YSZ composite cathodes showed substantially lower overall interfacial resistance values than LSM, but exhibited an additional arc attributed to the resistance of YSZ grain boundaries within the LSM–YSZ. At 850°C and low P_O2, an additional arc was observed with size varying as (P_O2)^−0.80 for LSM and (P_O2)^−0.57 for LSM–YSZ, suggesting that diffusion had become an additional rate limiting step. Bilayer LSM/LSM–YSZ electrodes yielded results intermediate between LSM and LSM–YSZ. The results showed that most of the improvement in electrode performance was achieved for a LSM–YSZ layer only ≈2 μm thick. However, a decrease in the grain-boundary resistance would produce much better performance in thicker LSM–YSZ electrodes.     

New red Y0.85Bi0.1Eu0.05V1−yMyO4 (M=Nb, P) phosphors for light-emitting diodes

The Y_0.85Bi_0.1Eu_0.05V_1−yM_yO₄ (M=Nb, P) as new near-ultraviolet excited phosphors were synthesized and their luminescence properties under 365 nm excitation were investigated in detail. It indicated that by doping small amount of P⁵⁺ into V⁵⁺ sites, the excitation intensity of charge transfer (CT) band of Bi–O (330–400 nm) was greatly improved. By substituting Nb⁵⁺ for V⁵⁺, both the CT bands of Bi–O and Eu–O (240–320 nm) were significantly enhanced. As a result, the emission intensity of Y_0.85Bi_0.1Eu_0.05V_1−yM_yO₄ (M=Nb, P) could be improved about 90% by doping 5 mol% P⁵⁺ and 110% by doping 5 mol% Nb⁵⁺. Comparing with the commercial Y₂O₂S:Eu³⁺ phosphors, the Y_0.85Bi_0.1Eu_0.05V_0.95M_0.05O₄ (M=Nb, P) phosphors exhibited excellent color purity and much higher brightness. The results showed that these Y_0.85Bi_0.1Eu_0.05V_1−yM_yO₄ (M=Nb, P) phosphors could be considered as promising red phosphors for application in LED.     

On the luminescence of LiBaF3:Eu

From the temperature dependence of the line—band luminescence intensity ratio of LiBaF₃:Eu²⁺ a 4f−5d activation energy (Δ) of 800 cm⁻¹ is derived, being much higher than the value reported in the literature (100 cm⁻¹). The temperature dependence of the luminescence decay can be well described with Δ = 800 cm⁻¹ and with 4f−4f and 5d−4f radiative probabilities of 4×10²s⁻¹ and 6×10⁵s⁻¹, respectively.