Effect of Oxygen-Deficiency of CuO2 Plane on the Structure, Magnetism, and Transport Properties

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 1.0) and the corresponding vacuum annealed samples were investigated systematically by means of XRD, infrared (IR) spectra, ESR, and resistivity. It is found that the doping of Sr and the oxygen vacancies in CuO₂ planes show different effects on the lattice parameters a and c, and the changes of a and c of La_{2 – x} Sr _x CuO_{4 –} samples (x 0.2) rest with the cooperation of the two factors. The two high frequency IR vibration modes at 500 and 689 cm^–1, which are referred to the vibrations of apical oxygen and planar oxygen, are analyzed in detail. The disappearance of the mode at 689 cm^–1 is interpreted in terms of the screened effect of charge carriers in CuO₂ planes. ESR results indicate that oxygen deficiency of CuO₂ layers not only decreases carrier concentration, but also destroys the antiferromagnetic spin correlation or spin fluctuation and results in localized Cu²⁺ spins. The effect of localized Cu²⁺ spins (or spin scattering) on the superconductivity and transport properties is discussed in the text.     

Structure, Phonon Vibration, and Spin Correlation of LaBa2Cu3?xCoxOy

Polycrystalline samples LaBa₂Cu_3–xCo _x O _y (0 x 1.0) were synthesized by solid state reaction method. The structure, phonon vibration, conduction, and spin correlation were investigated by means of X-ray diffraction, infrared spectra, resistivity, and electron spin resonance. It is found that there are orthorhombic–tetragonal and tetragonal–orthorhombic structural transitions with Co doping, and the conduction behavior changes from metallic to semiconducting. With the increase of Co content, the Cu(1)—O(1) phonon mode around 531 cm^–1 softens, the Cu(2)—O(2) phonon mode around 657 cm^–1 hardens, and the Cu(1)—O(4) mode around 583 cm^–1 is nearly unchanged. The Cu²⁺ spins tend to localize with Co doping. The changes in structure, phonon vibration, and spin correlation with Co doping are analyzed and discussed.     

In–Plane and Out–of–Plane Optical Properties of NdBa2Cu3Ox Single Crystals Close to x = 7.0

We present results of reflectivity measurements with EcandE c on NdBa ₂ Cu ₃ O _x (Nd123) single crystals close to full oxygen doping. Along the c–axis the optical conductivity shows a well developed absorption band around 450 cm ^–1 at all temperatures. The in–plane optical properties are dominated by crystal–field excitations at low energies, a prominent step at 400 cm ^–1 and a weaker feature between 500 - 550 cm ^–1. A comparison of and the in–plane scattering rate _ab () with neutron scattering derived spin susceptibility spectra suggests that the in–plane and out–of–plane anomalies are caused by the same mechanism, probably electron–spin scattering.     

Mechanical properties of thermosets

The tensile properties of a DGEBA (diglycidylether of bisphenol A)-norbornene anhydride network (T _g130±5 °C), were studied in the range (220 K-T _g); 4×10^–4 to 14×10^–3S^–1. The viscoelastic spectrum (1 Hz) reveals a low transition at 220 K. The bulk modulus is practically constant between 200 K andT _g — 20 K. The Poisson's ratio increases very slowly untilT _g — 30 K. Then it increases rapidly to reach its asymptotic value (0.5) near toT _g. The tensile (E) and shear (G) moduli display the classical behaviour linked to viscoelasticity. Plastic yielding occurs atT 80 °C, the elongation at yield is almost temperature and strain rate independent (G3_y = 0.035), whereas the yield stress obeys Kambour's relationship: _y = 1.1 (T _g —T) and Eyring's law (activation volume = 914cm³mol^–1). Physical ageing at 120 °C strongly affects the yield stress and the ductility. The maximum draw ratio, obtained atT T _g, is _RC = 1.35, which seems to be consistent with the network's crosslink density.     

Investigation of the temperature dependence of electron and phonon Raman scattering in single crystal YBa2Cu3O6.952

Detailed Raman-scattering measurements have been performed on high-quality YBa₂Cu₃O_6.952 single crystal (T _c =93 K, T _c =0.3 K). A sharp (FWHM 7.2 cm^–1 at 70 K and 10.0 cm^–1 at 110 K) 340 cm^–1phonon mode has been observed inB _1g polarization. An electronic scattering peak at 500 cm^–1 in theB _1g polarization extends down to 250 cm^–1. These FWHM values determine the upper limit of the homogeneous linewidth of the phonon and electronic excitations. The start of the electronic spectral function renormalization and of the 340 cm^–1 mode anomalies (frequency softening, linewidth sharpening, and intensity increase) have been observed to occur approximately 40 K aboveT _c . The 340 cm^–1 mode Fano shape analysis has been performed and the temperature dependences of the Fano shape parameters have been estimated. All 340 cm^–1 mode anomalies have been explained by the electronic spectral function renormalization.This work was supported by Swedish Natural Sciences Research Council (G.B. and L.B.) and by the National Science Foundation (DMR 91-20000) through the Science and Technology Center for Superconductivity (G.B. and M.V.K.).     

Electronic Raman scattering of superconducting YBa2Cu3Oy single crystals

TheA _1g andB _1g low-energy Raman continua of YBa₂Cu₃O _y (Y123) single crystals, withy=7.0, 6.99, and 6.93, have been investigated. It is found that the peak frequency of theA _1g continuum is equal to 310±10 cm^–1 and independent of oxygen concentration fory in the above range. The central frequency of the broad peak in theB _1g continuum, however, shifts from about 470 cm^–1 fory7.0 to 550 cm^–1 fory6.93. Thus, a relatively small change in oxygen concentration results in a significant redistribution of the states contributing to theB _1g continuum. Assuming the low-energy portions of the continua are electronic in origin, the Raman spectra have been calculated and the results compared to the experimental spectra. It is suggested that the Raman continua arise, at least in part, from scattering across a spin fluctuation-induced pseudogap.     

FeCl3-doped polyvinylidene fluoride

Infrared (350–4000 cm^–1) and optical (1.15×10⁴–2.95×10⁴cm^–1) spectra, differential thermal analysis (DTA) and d.c. electrical resistivity of FeCl₃- doped polyvinylidene fluoride (PVDF) films, over the doping mass fraction range 0 w 0.40, have been measured. The i.r. spectra provided evidence of: (a) the presence of both and phases in the undoped, and a phase in the doped PVDF films; (b) a head-to-head content of 20%; and (c) a different doping mode beyond a 0.25 doping level. The optical spectra resulted in two induced energy bands, and a probable interband electronic transition, due to doping. Dipole relaxation and premelting endothermic peaks were identified by DTA. Electrical conduction is thought to proceed by interpolaron hopping among the polaron and bipolaron states induced by doping. The hopping distance, R _o, is calculated according to the Kuivalainen model. A numerical equation is adopted to formulate the dependence of R _oon doping level and temperature. It is found that R _o< CC separation length. This implies that, in doped PVDF, charge carrier hopping is not an intrachain process.     

Treasure of the Past X: A Spectroscopic Determination of Scattering Lengths for Sodium Atom Collisions

We report a preliminary value for the zero magnetic field Na ²S(f = 1, m = − 1) + Na ²S(f = 1, m = − 1) scattering length, a_1,−1. This parameter describes the low-energy elastic two-body processes in a dilute gas of composite bosons and determines, to a large extent, the macroscopic wavefunction of a Bose condensate in a trap. Our scattering length is obtained from photoassociative spectroscopy with samples of uncondensed atoms. The temperature of the atoms is sufficiently low that contributions from the three lowest partial waves dominate the spectrum. The observed lineshapes for the purely long-range 0g− molecular state enable us to establish key features of the ground state scattering wavefunction. The fortuitous occurrence of a p-wave node near the deepest point (R_e = 72 a₀) of the 0g− potential curve is instrumental in determining a_1,−1 = (52 ± 5) a₀ and a_2.2 = (85 ± 3) a₀, where the latter is for a collision of two Na ²S(f = 2, m = 2) atoms.     

A Spectroscopic Determination of Scattering Lengths for Sodium Atom Collisions

We report a preliminary value for the zero magnetic field Na ²S(f = 1, m = − 1) + Na ²S(f = 1, m = − 1) scattering length, a_1,−1. This parameter describes the low-energy elastic two-body processes in a dilute gas of composite bosons and determines, to a large extent, the macroscopic wavefunction of a Bose condensate in a trap. Our scattering length is obtained from photoassociative spectroscopy with samples of uncondensed atoms. The temperature of the atoms is sufficiently low that contributions from the three lowest partial waves dominate the spectrum. The observed lineshapes for the purely long-range 0g− molecular state enable us to establish key features of the ground state scattering wavefunction. The fortuitous occurrence of a p-wave node near the deepest point (R_e = 72 a₀) of the 0g− potential curve is instrumental in determining a_1,−1 = (52 ± 5) a₀ and a_2,2 = (85 ± 3) a₀, where the latter is for a collision of two Na ²S(f = 2, m = 2) atoms.     

An assessment of expressions for the apparent thermal conductivity of cellular materials

Diverse expressions for the thermal conductivity of cellular materials are reviewed. Most expressions address only the conductive contribution to heat transfer; some expressions also consider the radiative contribution. Convection is considered to be negligible for cell diameters less than 4 mm. The predicted results are compared with measured conductivities for materials ranging from fine-pore foams to coarse packaging materials. The dependencies of the predicted conductivities on the material parameters which are most open to intervention are presented graphically for the various models.Nomenclature a Absorption coefficient - C _v (Jmol^–1 K^–1) Specific heat - E Emissivity - E _L Emissivity of hypothetical thin parallel layer - E ₀ Boundary surfaces emissivity - f Fraction of solid normal to heat flow - fics Fraction of total solid in struts of cell - K(m^–1) Mean extinction coefficient - k(W m^–1 K^–1) Effective thermal conductivity of foam - k _cd(W m^–1 K^–1) Conductive contribution - k _cr(W m^–1 K^–1) Convective contribution - k _g(W m^–1 K^–1) Thermal conductivity of cell gas - k _r(W m^–1 K^–1) Radiative contribution - k _s(W m^–1 K^–1) Thermal conductivity of solid - L(m) Thickness of sample - L _g(m) Diameter of cell - L _s(m) Cell-wall thickness - n Number of cell layers - r Reflection coefficient - t Transmission coefficient - T(K) Absolute temperature - T _m(K) Mean temperature - T _N Fraction of energy passing through cell wall - T ₁(K) Temperature of hot plate - T ₂(K) Temperature of cold plate - V _g Volume fraction of gas - V _w Volume fraction of total solid in the windows - w Refractive index - (m) Effective molecular diameter - (Pa s) Gas viscosity - Structural angle with respect to rise direction - (W m^–2 K^–4) Stefan constant     

Optical and electrical properties of electrodeposited silver based thin films

The electrodeposited superionic conductor Ag₆I₄WO₄ was doped with various concentrations of [CrO₄]^2– to form the quarternary compound Ag₆I₄WO_4(1–xCrO_4(x). The doping level,x, was varied from 0 to 0.6 and the optimum compound was used for further analysis. X-ray diffraction (XRD) analysis indicated major peaks occurring atd values of 3.75,2.29,1.96 and 3.96 in the order of decreasing intensity. The energy dispersive analysis of X-rays (EDAX) technique verified quantitatively the ratio of the components in the solid electrolyte. From the fringes seen in the interference pattern of the transmission spectrum, the refractive index and thickness of the film was calculated. The absorption spectrum indicated the characteristic chromate peak at 310 nm when the dopant was present. An open circuit voltage (OCV) of 670 mV was observed for the fabricated cells with optimum performance at a doping level ofx=0.1, where the best discharge characteristics were observed. The subsequent conductivity was calculated to be of the order 10^–3–1 cm^–1 from the Cole-Cole plot.     

Devitrification and vitrification of tellurite glasses

The crystallization of pure tellurite glass during various heating rates was studied. The activation energy for crystallization was 115 × 10²² eV mol^–1. The glass transformation, T _g, starting crystallization, T _x, crystallization, T _c and melting temperatures, T _m, have been reported for binary tellurite glasses of the form (1 – x) TeO₂–xA_nO_m [A_nO_m = MnO₂, Co₃O₄ and MoO₃]. Among many different parameters of the glass forming potential the two-thirds rule, T _g/T _m, the glass stabilization range, T= T _x – T _g, and the glass forming tendency, K _g= (T _c– T _g)/(T _m – T _c), are reported for the first time for tellurite glasses.     

The crystallization and electrical properties of lead-based ferroelectric thin films for uncooled pyroelectric infrared detector

Epitaxially grown and polycrystalline PT, PLT and PZT thin films with thickness from 1 to 2 m have been prepared on Pt/Ti/SiO₂/Si substrates by means of the modified sol–gel spin-coating technique. The ferroelectric thin films have good crystallization behavior, excellent dielectric and pyroelectric properties. The pyroelectric coefficients of PT and PLT thin films are 2.9×10^–8 C/cm² k and (3.37–5.25)×10^–8 C/cm² k, respectively. The figures of merit for voltage responsivity of PT and PLT thin films (F _I ) are 0.60×10^–10 Ccm/J and (0.79–1.13)×10^–8 Ccm/J, respectively. The figures of merit for current responsivity of these films are 9.0×10^–9 Ccm/J and (10.5–16.0)×10^–9 Ccm/J, and the figures of merit for detectivity of these films are 0.74×10^–8 Ccm/J and (0.79–1.13)×10^–8 Ccm/J, respectively.     

An assessment of expressions for the apparent thermal conductivity of cellular materials

Diverse expressions for the thermal conductivity of cellular materials are reviewed. Most expressions address only the conductive contribution to heat transfer; some expressions also consider the radiative contribution. Convection is considered to be negligible for cell diameters less than 4 mm. The predicted results are compared with measured conductivities for materials ranging from fine-pore foams to coarse packaging materials. The dependencies of the predicted conductivities on the material parameters which are most open to intervention are presented graphically for the various models.Nomenclature a Absorption coefficient - C _itv(J mol^–1 K^–1) Specinc heat - E Emissivity - E _L Emissivity of hypothetical thin parallel layer - E _o Boundary surfaces emissivity - f Fraction of solid normal to heat flow - f _s Fraction of total solid in struts of cell - K(m^–1) Mean extinction coefficient - k(Wm^–1 K^–1) Effective thermal conductivity of foam - k _cd(Wm^–1 K^–1) Conductive contribution - k _cr(Wm^–1 K^–1) Convertive contribution - k _g(Wm^–1K^–1) Thermal conductivity of cell gas - k _r(Wm^–1 K^–1) Radiative contribution - k _s(Wm^–1 K^–1) Thermal conductivity of solid - L(m) Thickness of sample - L _g(m) Diameter of cell - L _s(m) Cell-wall thickness - n Number of cell layers - r Reflection coefficient - t Transmission coefficient - T(K) Absolute temperature - T _m(K) Mean temperature - T _N Fraction of energy passing through cell wall - T ₁(K) Temperature of hot plate - T ₂(K) Temperature of cold plate - V _g Volume fraction of gas - V _w Volume fraction of total solid in the windows - w Refractive index - (m) Effective molecular diameter - (Pa s) Gas viscosity - Structural angle with respect to rise direction - (Wm^–2 K^–4) Stefan constant     

Space charge limited current, variable range hopping and mobility gap in thermally evaporated amorphous InSe thin films

We have analyzed the properties of as-deposited InSe thin films, deposited onto well cleaned glass substrates under a vacuum of 10^–5 Torr, using X-ray diffraction, Rutherford back scattering, energy dispersive analysis of X-rays, optical transmittance and current–voltage (120–390 K) measurements. Allowed and indirect transition was identified and the mobility gap was determined as 1.44 eV. Under low field (<1×10⁵ V cm^–1) and in the temperature range of 130–200 K, the conductivity in the films was behaving like that of Mott's variable-range hopping (VRH) type. Mott's parameters such as characteristics temperature (T ₀), hopping range (R _hop), hopping energy (W _hop), values of localized states density N (E _F), and activation energy (E _a) were estimated. In the temperature range 210–290 K, thermionic conduction mechanism plays a dominant role and its activation energy was calculated. At high field (>2×10⁵ V cm^–1) and in the temperature range of 300–390 K, space charge limited conduction currents (SCLC) mechanism was observed and the related parameters, such as electron density (n ₀), trap density (n _t), the ratio between free electron density to the total electron density (), mobility () and the effective mobility (_eff) of the InSe film of typical thickness 265 nm were calculated and the results are discussed.     

The high-temperature thermal expansion of BiPbSrCaCuO superconductor and the oxide components (Bi2O3, PbO,CaO, CuO)

The thermal expansion of superconducting Bi_1.6Pb_0.4Sr₂Ca₂Cu₃Ox (BiPbSrCaCuO) and its oxide components Bi₂O₃, PbO, CaO and CuO have been studied by high-temperature dilatometric measurements (30–800°C). The thermal expansion coefficient for the BiPbSrCaCuO superconductor in the range 150–830°C is =6.4×10^–6K^–1. The temperature dependences of L/L of pressed Bi₂O₃ reveals sharp changes of length on heating (T ₁=712°C), and on cooling (T ₂=637°C and T ₃=577°C), caused by the phase transition monoclinic-cubic (T ₁) and by reverse transitions via a metastable phase (T ₂ and T ₃). By thermal expansion measurements of melted Bi₂O₃ it is shown that hysteresis in the forward and the reverse phase transitions may be partly caused by grain boundary effect in pressed Bi₂O₃. The thermal expansion of red PbO reveals a sharp decrease in L/L, on heating (T ₁=490°C), related with the phase transition of tetragonal (red, a=0.3962 nm, c=0.5025 nm)-orthorhombic (yellow, a=0.5489 nm, b=0.4756 nm, c=0.5895 nm). The possible causes of irreversibility of the phase transition in PbO are discussed. In the range 50–740°C the coefficient of thermal expansion of pressed Bi₂O₃ (_m=3.6 × 10^–6 and _c=16.6×10^–6K^–1 for monoclinic and cubic Bi₂O₃ respectively), the melted Bi₂O₃ (_m=7.6×10^–6 and _c=11.5×10^–6K^–1), PbO (_t=9.4×10⁶ and _or=3.3×10^–6K^–1 for tetragonal and orthorhombic PbO respectively), CaO (=6.1×10^–6K^–1) and CuO (=4.3×10^–6K^–1) are presented.     

Study of La1−xMnO3−δ non-stoichiometry and defect structure using ESR and iodometry

The oxidation states of manganese in the La_1–xMnO_3– (x = 0.09–0.11) were investigated by electron spin resonance (ESR) and iodometry. The ESR analysis carried out at room temperature for the samples prepared in air revealed the presence of broad peaks at g = 2.0, considered to be relevant to Mn²⁺. It was also found that the intensity of the peak increased as lanthanum vacancy content increased. The average valence state of manganese, determined by iodometry, was approximately 3.2, and decreased by 1 as the lanthanum vacancy increased by 1. Similar trends were observed with the samples prepared at P _{o 2} = 1×10^–7. The results indicated that Mn²⁺ is stably present in the La_1–xMnO_3– having an average valence number exceeding 3.0. A series of experimental results with respect to the non-stoichiometry of La_1–xMnO_3– can be explained by assuming that Mn²⁺ is stabilized after forming a complex with a lanthanum vacancy and two oxygen vacancies.     

The Second Order Recombination and Spin-Exchange Relaxation of Atomic Deuterium at Low Temperatures in a Low Magnetic Field

We measured the 2nd order recombination rates and spin-exchange relaxation of atomic deuterium (D) in a ⁴ He coated sample cell, using the hyperfine resonance of (F = 1/2, m_F = –1/2) – (F = 3/2, m_F = –1/2) transition in a low magnetic field (3.9 mT) at temperatures between 0.6 K and 1.2 K. At lower temperatures below 0.9 K, the density decay of D atoms was dominated by D-D recombination on the liquid He surface. We found that the surface recombination cross length was 1_DD = (5.5 ± 1.3) × 10 ^–9 cm and the adsorption energy of D on ⁴ He surface was _a = 3.97 ± 0.07 K. Compared with prior measurements at high magnetic fields by other groups, 1_DD at low field was orders of magnitude smaller than what was expected when the scaling of 1/B² dependence of the direct recombination mechanism was used, and in addition, _a was significantly larger. This was attributed to the onset of the resonant recombination mechanism for the D-D surface recombination at high fields. Above 0.9 K, D-D volume recombination and recombination of D with hydrogen impurity became dominant processes of the density decay of D. The transverse relaxation times were measured and we determined the D-D spin-exchange relaxation rates, G_DD = (1.4 ± 0.6) × 10 ^–10 cm ³ sec ^–1 . It was smaller than theoretical calculations.     

Synthesis of ZnFe2O4–Zn2ZrO4Solid Solutions

Low-temperature plasma synthesis was used to prepare solid solutions ( and ) in the ZnFe₂O₄–Zn₂ZrO₄pseudobinary system. The Zn_{2 – x} Zr_{1 – x} Fe_2x O₄solid solutions were found to have a tetragonal spinel structure (a= 8.607–8.740 Å, c= 8.798–9.120 Å) in the composition range x= 0–0.55 and a cubic spinel structure (a= 8.447–8.539 Å) at x= 0.75–1.0. The tetragonal lattice distortion is attributed to a pseudo-Jahn–Teller effect. The electrical conductivity of the solid solutions shows semiconducting behavior and rises by a few orders of magnitude with increasing Fe³⁺content.     

Transport properties of InSe x flash evaporated thin films

Thin films of InSe _x were obtained by vacuum evaporation of polycrystalline materials onto substrates at moderate temperatures,T _s. Electrical properties of films grown from different stoichiometries of flash source materials are reported in this work. The temperature dependence of the conductivities shows two conduction regimes. The low temperature regime exhibits aT ^–1/4 conductivity dependence which fits well, using the Mott model, with an average localized states density value ofN(E _F ) 8×10¹⁸cm^–3eV^–1. Hall measurements as a function of temperature show that the predominant conduction mechanism is scattering by grain boundaries in polycystalline films.