Effects of Substituting Ni and Zn for Cu in the Electron Doped Sr0.9La0.1CuO2 Superconductor

We used X-ray diffraction, energy dispersive spectroscopy and low field magnetization to characterize Sr_0.9La_0.1Cu_1–x R _x O₂ samples for R=Zn and Ni. We found that both Ni and Zn are substituted at the Cu-site. The value of T _c was almost independent of composition until x0.03 for R=Zn while it was reduced to 30 K at x0.02 for R=Ni. This trend of T _c reduction is very similar to the pair breaking-effect in conventional superconductors and electron-doped (Nd, Ce)₂CuO_4– but the rate of reduction of T _c for R=Ni is larger in Sr_0.9La_0.1CuO₂ than in (Nd, Ce)₂CuO_4–. These results are discussed along with the recent experimental observation of gap symmetry in electron-doped superconductors.     

δ-FeO (OH) and its solutions

Decomposition products of -FeO(OH)-type Fe_1–x M _x O_1–x (OH)_1+x phases (M=Mg, Zn, Ca, Cd) have been studied by X-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. It has been shown that the M=Mg and Cd -phases decompose to -Fe₂O₃-based solid solutions which in turn undergo exsolution to form some MgO and CdO at a higher temperature. In the case of Fe_1–x Zn _x O_1–x (OH)_1+x , the decomposition proceeds over -Fe₂O₃ ss to an unstable spinel solid solution. All decomposition products are topotactically related to their precursors in the decomposition chain. In the electron microscope some -type phases undergo in situ decomposition under intense beam bombardment with somewhat different results than obtained for thermal decomposition products under ambient conditions. The plate-like morphology and crystal size is retained in the decomposition products; however, the products have a more pitted appearance after decomposition.     

Reactivity of oxygen-deficient Mn(II)-bearing ferrites (Mn x Fe3-x O4-δ, O⩽x⩽1, δ>0) toward CO2 decomposition to carbon

The reduction of CO₂ to carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (Mn _x Fe_3-x O_4-, Ox1, >0) at 300 °C. They were prepared by reducing Mn(II)-bearing ferrites with H₂ gas at 300°C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO₂ to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mössbauer study of the phase changes of the solid samples during the H₂ reduction and CO₂ decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, , contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO₂ to carbon by the donation of an electron at adsorption sites.     

600°C Section of the Fe–FeS–NiS–Ni Phase Diagram

The 600°C section of the Fe–FeS–NiS–Ni phase diagram was studied by optical and electron microscopy techniques, x-ray diffraction, and electron probe x-ray microanalysis. The results agree with the most reliable data available in the literature. The solid-solution regions identified are those of (Fe _z Ni_{1 – z} )_{3 ±} S₂(high-temperature heazlewoodite structure), (Fe _z Ni_{1 – z} )S_{1 +} , (Fe _z Ni_{1 – z} )_{9 +} S₈(pentlandite structure), -(Fe,Ni), and -(Fe,Ni). The section also contains seven two-phase and three three-phase regions. The S content of the monosulfide solid solution attains 50.8 at. % at Ni : (Ni + Fe) = 0.6 and 54.0 at. % at Ni : (Ni + Fe) = 0.2. The heazlewoodite solid solution contains up to 26 at. % Fe (at 44.3 at. % S). The highest Ni content of the pentlandite solid solution is 22.5 at. % at 47.5 at. % S and 32.0 at. % at 46.2 at. % S.     

Specific heat measurements of intercalation compounds M x TiS2 (M=3d transition metals) using ac calorimetry technique

Specific heats of 3d transition metal intercalates of 1T-CdI₂-type TiS₂, M _x TiS₂ (M=V, Cr, Mn, Fe, Co, and Ni; 0x1), have been measured in the temperature range 1.6–300 K using an ac calorimetry technique. The electronic specific heat coefficient (2–100 mJ/mole K²) and the Debye temperature _D (240–430 K) are found to depend on the guest 3d metals and their concentrations. All the intercalates show anomalous specific heat at low temperatures following an – lnT dependence ( and are constants), as found in dilute alloys.     

Influence of preparation method on catalytic properties of mixed calcium-cobalt orthophosphates

Mixed calcium-cobalt orthophosphates of the formula Ca_3–x CO_x(PO₄)₂, with 0 x 1.1, were prepared by coprecipitation and solid-state reaction. Structural characterization showed that, in both cases, the solids obtained resulted from substitution of some Ca²⁺ ions by Co²⁺ ions in the -Ca₃(PO₄)₂ structure. The solubility limit of cobalt in this structure corresponded tox=0.31. The morphology of these compounds was investigated by surface-area measurements and scanning electron microscopy. When tested in the 2-propanol decomposition reaction, the maximum activity in dehydrogenation was obtained with the compound corresponding to cobalt maximum solubility in -Ca₃(PO₄)₂ structure. Higher activities were obtained for samples prepared by coprecipitation.     

Electrical conduction in γ-irradiated and unirradiated zinc-iron ferrites

The electrical conductivity of -irradiated and unirradiated finely-divided spinels of composition (Zn _x ²⁺ Fe _1–x ²⁺ Fe ₂ ³⁺ )O ₄ ^2– was studied in a nitrogen atmosphere as a function of temperature. The results of both -irradiated and unirradiated ferrites with compositions x 0.79 showed that the electrical conduction occurred by fast electron exchange amongst Fe²⁺ and Fe³⁺ ions situated on octahedral sites in the spinel lattice, by a hopping mechanism. For composition x > 0.79 it was found that the transition of the charge carriers through cation vacancies is the predominant mechanism. Some breaks in the conductivity-temperature curves were found near the Curie points. Seebeck voltage measurements showed that -irradiated and unirradiated spinels behave as n-type semiconductors. The effect of -irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.     

Effect of Crystal Structure on the Electrical Properties of CaTi1 – xFexO3 – δ

The electrical conductivity of CaTi_{1 – x} Fe _x O_{3 –} (x= 0–0.5) was measured as a function of temperature and oxygen partial pressure. At 1000°C, the highest conductivity was observed at x= 0.2. The crystal structure of the materials with x= 0, 0.2, 0.25, and 0.3 was studied by x-ray powder diffraction and refined by the full-profile analysis method. The results were used to elucidate the mechanisms of the high-temperature (1000°C) formation, ordering, and transport of oxygen vacancies in CaTiO₃upon substitution of Fe³⁺for Ti⁴⁺. The composition dependences of ionic conductivity calculated for CaTi_{1 – x} Fe _x O_{3 –} agree well with experiment.     

Relative permittivity and dielectric loss tangent of substrate materials for high-Tc superconducting film

We measure the relative permittivity _r and dielectric loss tangent tan of substrate materials for high-T _c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO₃, YAlO₃, LaSrGaO₄, NdGaO₃, sapphire, and ZrO₂ ceramic. The _r values are 10–30 and become almost constant below about 50 K. The tan values decrease with decreasing temperature and are below 1×10^–5 at 77 K except for those of NdGaO₃ and ZrO₂ ceramic. This suggests that the tan values of MgO, LaAlO₃, YAlO₃, LaSrGaO₄, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T _c superconducting films. It is also demonstrated that the tan of the substrate material is strongly affected by impurities.     

Superconductivity of (Y1−xREx)Ba2Cu3O7#x2212;δ system

Polycrystalline samples of the superconducting oxides (Y_1–x RE _x )Ba₂Cu₃O_7– (RE = Er and Dy) withx=0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared. From the X-ray diffraction and the electrical resistivity measurements, it was found thatT _c and the unit cell volume have common peaks nearx0.4. Close examination of previously published data on the (Y_1–xRE _x )Ba₂Cu₃O_7– system also indicate that an anomaly exists nearx–0.4. This anomaly is ascribed to an anomalous change of in oxygen nearx0.4.     

Oxygen Loss of the Manganite Surface Layer in La1 ? δMnO3/Metal Interface. Transport, XPS, and Photoconductivity Measurements

We report electrical measurements, XPS measurements, and photoconductivity on La_{1 –} MnO₃/metal interfaces. A clear evidence of a photo-induced insulator–metal transition of a La_0.81MnO₃/Al/Al₂O₃/Nb tunnel junction and second peak on R–T dependence of LaMnO₃/metal junctions are reported. These effects are explained in terms of formation of the La_{1 –} MnO₃ oxygen depleted layer caused by the out-diffusion of oxygen in La_{1 –} MnO₃/metal interface.     

Fabrication of bulk superconductors YBa2Cu3?xTexO7?δ with highly oriented layer structure using the melt-texture growth process

We report on the successful fabrication of bulk samples satisfying the nominal composition YBa₂Cu_3–x Te _x O_7– and containing highly single-crystal-like texture. While this type of crystal growing process is not new, our process requires only the existence of spatial temperature gradient in some parts of the common tube furnace. The samples with tellurium were found to be much more stable and better superconductors than the Y-123 specimen. Large layer textures with cross-section 50×500m² were observed to grow inside the usual bulk sample. The critical currents were measured by the d.c. magnetization method and found to be easily greater than 6000 A cm^–2 for the samples with Te.     

IR Spectra of La1.85Sr0.15Cu1?xMxO4?δ(M = Zn, Ni, Mg)

Polycrystalline samples La_1.85Sr_0.15Cu_1–xZn_xO_4– (0 x 0.3), La_1.85Sr_0.15Cu_1–xNi_xO_4– (0 x 0.3), and La_1.85Sr_0.15Cu_1–xMg_xO_4– (0 x 0.3) were synthesized by the solid-state reaction method. The crystal structure and phonon vibration were investigated by means of X-ray diffraction (XRD) and infrared spectrum. Zn, Ni, and Mg doping results in the lattice parameter c decreasing and a (b) increasing. The change of the phonon modes around 504 cm^–1 and 681 cm^–1 can be satisfactorily interpreted in terms of the change of the crystal structure and the itinerant nature of charge carrier in CuO₂ sheet. The relation between the structure and phonon vibration is discussed.     

IR Spectra of La1.85Sr0.15Cu1?xMxO4?δ(M = Zn, Ni, Mg)

Polycrystalline samples La_1.85Sr_0.15Cu_1–xZn_xO_4– (0 x 0.3), La_1.85Sr_0.15Cu_1–xNi_xO_4– (0 x 0.3), and La_1.85Sr_0.15Cu_1–xMg_xO_4– (0 x 0.3) were synthesized by the solid-state reaction method. The crystal structure and phonon vibration were investigated by means of X-ray diffraction (XRD) and infrared spectrum. Zn, Ni, and Mg doping results in the lattice parameter c decreasing and a (b) increasing. The change of the phonon modes around 504 cm^–1 and 681 cm^–1 can be satisfactorily interpreted in terms of the change of the crystal structure and the itinerant nature of charge carrier in CuO₂ sheet. The relation between the structure and phonon vibration is discussed.     

The thermal conductivity of propane

This paper presents thermal conductivity measurements of propane over the temperature range of 192–320 K, at pressures to 70 MPa, and densities to 15 mol · L^–1, using a transient line-source instrument. The precision and reproducibility of the instrument are within ±0.5%. The measurements are estimated to be accurate to ±1.5%. A correlation of the present data, together with other available data in the range 110–580 K up to 70 MPa, including the anomalous critical region, is presented. This correlation of the over 800 data points is estimated to be accurate within ±7.5%.Nomenclature a _n, b_ij, b_n, c_n Parameters of regression model - C Euler's constant (=1.781) - P Pressure, MPa (kPa) - P _cr Critical pressure, MPa - Q ₁ Heat flux per unit length, W · m^–1 - t time, s - T Temperature, K - T _cr Critical temperature, K - T ₀ Equilibrium temperature, K - T _re Reference temperature, K - T _r Reduced temperature = T/T _cr - T _TP Triple-point temperature, K Greek symbols Thermal diffusivity, m² · s^–1 - T _i Temperature corrections, K - T Temperature difference, K - T _w Temperature rise of wire between time t ₁ and time t ₂, K - T ^* Reduced temperature difference (T–T _cr)/T_cr - _corr Thermal conductivity value from correlation, W · m^–1 · K^–1 - _cr Thermal conductivity anomaly, W · m^–1 · K^–1 - _e Excess thermal conductivity, W · m^–1 · K^–1 - ^* Reduced density difference - Thermal conductivity, W^–1 · m^–1 · K^–1, mW · m^–1 · K^–1 - _bg Background thermal conductivity, W · m^–1 · K^–1 - ₀ Zero-density thermal conductivity, W · m^–1 · K^–1 - Density, mol · L^–1 - _cr Critical density, mol · L^–1 - _re Reference density, mol · L^–1 - _r Reduced density Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Phonon Vibration and Conduction of La2 ? xSrxCuO4 ? δ and La1.85 ? xSr0.15 + xCu1 ? xCoxO4 ? δ

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 0.5) and La_{1.85 – x} Sr_{0.15 + x} Cu_{1 – x} Co _x O_{4 –} (0 x 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane stretching vibration mode (689 cm^–1). The softening of the phonon vibration mode gives an index of the weakening of hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

Radiation of internal waves during vertical motion of a body through a nonuniform liquid

Energy losses to radiation of internal waves during the vertical motion of a point dipole in two-dimensional and three-dimensional cases are computed.Notation _o(z), p_o(z) density and pressure of the ground state - z vertical coordinate - v, p, perturbed velocity, pressure, and density - H(d 1n _o/dz)^–1 characteristic length scale for stratification - N=(gH^–1–g²c _o ^–2 )^1/2 Weisel-Brent frequency - g acceleration of gravity - c_o speed of sound - vertical component of the perturbed velocity - V vector operator - k wave vector - frequency - d vector surface element - W magnitude of the energy losses - (t), (r) (x)(y)(z) Dirac functions - v_o velocity of motion of the source of perturbations - d dipole moment of the doublet - _o,l length dimension parameters - _o intensity of the source Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 619–623, October, 1980.     

Electrical properties of BaSnO3 in substitution of antimony for tin and lanthanum for barium

Polycrystalline materials of BaSn_1–x Sb _x O_3– and Ba_1–y La _y SnO_3– were prepared. Substitutional solubilities of antimony for tin and lanthanum for barium, respectively, in BaSnO₃ were obtained to be x=0.18 for BaSn_1–x Sb _x O_3– and y<0.052 for Ba_1-y La _y SnO_3–. The X-ray photoemission spectroscopy measurements showed the valence of antimony and tin is mixed in our samples of BaSn_1–x Sb _x O_3–. At lower temperature, magnetic susceptibilities of BaSn_1–x Sb _x O_3– and Ba_1–y La _y SnO_3– satisfy the Curie law, indicating the existence of non-interacting localized electrons at the Sn⁴⁺ site, and forming a Sn⁴⁺+e^– state in these systems. By substitution of antimony and lanthanum in BaSnO₃, the conductive properties are semiconductor-like. To explain this conductive behaviour, three types of mechanism were taken into consideration.     

Ferroelectric Lead Zirconate Titanate Films Prepared by Spray Pyrolysis of Carboxylate Solutions

Ferroelectric PbTi_0.6Zr_0.4O₃films 0.5–1.5 m in thickness were produced on platinum substrates by spray pyrolysis of carboxylate solutions. The optimized compositions of the precursor solutions, containing methacrylic acid and ethylene glycol, are stable under normal conditions, allow the annealing temperature to be reduced, and lead to higher quality film surfaces and large grains. The film exhibit the following electrical properties: T _C= 360–460°C, _max= 1750 at T _C, tan = 0.02–0.1 at 1 kHz and room temperature, P _{s max} = 18 C/cm², P _{r max} = 15 C/cm²at 50 Hz, and E _c= 42–120 kV/cm.