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Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500 C to 1500 C by adding to it small amounts of calcium, barium, or strontium. This compound is an excellent thermoelectric material.
Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500 C to 1500 C by adding to it small amounts of calcium, barium. or strontium. This novel compound is an excellent thermoelectric material.
The relationship between emission properties and sample composition is studied for lanthanum-boron compounds. Specifically, the La-B system is considered between 1400 and 2100 K and between LaB(4.24) and LaB(29.2) to determine the phase relationship, chemical activity of the compounds, vapor composition, and vaporization rate. The results indicate that: (1) a blue-colored phase near LaB(9) exists between a purple-colored LaB(6) and elemental boron, (2) vaporization is sufficiently more rapid than diffusion so that great compositional differences exist between the surface and the interior, (3) an activation energy lowers the boron vaporization rate from LaB(6), and (4) a steady-state surface composition between LaB(6.04) and LaB(6.07) exists for freely vaporizing materials as a function of interior composition, purity, and temperature. It is noted that the ultimate life of a thermionic diode is governed by electrode vaporization rate whereas efficiency is governed by the electrode work function.
The electron-pairing mechanism in unconventional high-temperature superconductors (HTS) has not been resolved. We proposed that the electron-pairing medium of unconventional HTS is the change of the electron clouds of transition metal ions, which is analogous to the lattice vibration in conventional superconductors. Real-time evolution of the electron clouds of transition metal ions under excitations in La{sub 2}Fe{sub 2}As{sub 2}O{sub 2}, FeSe sheet, and HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8} was calculated by the time-dependent density functional theory (TDDFT). The characteristic frequencies are 160 meV, 190 meV, and 250 meV, respectively. The frequencies are close to that of the lattice vibration in conventional HTS at high pressures, showing that the change of the electron clouds of the transition metal ions can be the electron-pairing medium.
We report on the study of In substitution for Mn on the magnetic and transport properties of layered manganese oxides La{sub 0.7}Er{sub 0.05}Sr{sub 0.15}Ca{sub 0.1}Mn{sub 1−x}In{sub x}O{sub 3} (0 ≤ x ≤ 0.30) synthesized via sol-gel method. For all the samples, all peaks are satisfactorily indexed in the rhombohedra structure with R 3-bar c space group. Magnetic data, under a magnetic field of 0.05 T, revealed that our compounds exhibit a continuous (second-order) transition from a ferromagnetic (FM) to a paramagnetic (PM) state upon decreasing the temperature. Also, magnetic entropy change and relative cooling power for magnetic field variation were predicted. Then, we have fitted the experimental data of resistivity using non-linear curve fitting, a typical mathematical function (Gauss function). This function can describe the carrier transport behavior of manganites as a function of temperature around the electrical phase transition. The obtained results were discussed. These predicted parameters agree with the experimental data.
Recent observations of selective emergence (suppression) of superconductivity in the uncollapsed (collapsed) tetragonal phase of LaFe 2 As 2 has rekindled interest in understanding what features of the band structure control the superconducting $T_c$. In this work, we show that the proximity of the narrow Fe-$d_{xy}$ state to the Fermi energy emerges as the primary factor. In the uncollapsed phase this state is at the Fermi energy, and is most strongly correlated and a source of enhanced scattering in both single and two particle channels. The resulting intense and broad low energy spin fluctuations suppress magnetic ordering and simultaneously provide glue for Cooper pair formation. In the collapsed tetragonal phase, the $d_{xy}$ state is driven far below the Fermi energy, which suppresses the low-energy scattering and blocks superconductivity. A similar source of broad spin excitation appears in uncollapsed and collapsed phases of CaFe 2 As 2 . This suggests controlling coherence provides a way to engineer $T_c$ in unconventional superconductors primarily mediated through spin fluctuations.
Spectroscopic properties of mixed complexes with two different ligand groups surrounding lanthanide ion, discussing energy transfer and absorption
The magnetic properties of heterostructures consisting of two films are studied. The upper layer involves rare-earth intermetallic nanostructured superlattices consisting of exchange-coupled layers (TbCo{sub 2}/FeCo){sub n} (TCFC), and the lower layer includes either epitaxial manganite La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) with optimum strontium doping or an epitaxial film of an yttrium–iron garnet Y{sub 3}Fe{sub 5}O{sub 12} (YIG) with a Bi additive. TCFC is a ferromagnet having high Curie temperature and provides controllable induced magnetic anisotropy. Experimental studies showed that the interlayer interaction of the TCFC/LSMO heterostructure is antiferromagnetic. There was an increase in the FMR line width in the structures due to the flow of a spin current through the interface between two films. There was electric voltage in the TCFC/YIG heterostructure induced in the TCFC intermetallide film, due to an inverse spin Hall effect under ferromagnetic resonance conditions.
In this paper, we study the structural, magnetic, and magnetocaloric properties of the polycrystalline peroviskite manganites La{sub 0.5}Pr{sub 0.3}Ba{sub 0.2}Mn{sub 1-x}Ti{sub x}O{sub 3} with x = 0 and 0.1. Our samples were prepared by solid-state reaction method. The XRD study has been analyzed by Rietveld refinement technique. Both samples crystallize in the rhombohedral symmetry with R 3-bar c space group. The second order of magnetic phase transition in all samples is confirmed by the Arrott analysis and the behavior of the master curve. Moreover, the magnetic entropy change ∆S{sub M} has been determined by the Maxwell relation, using phenomenological model and Landau theory. The relative cooling power (RCP) value under a magnetic field of 5 T is 236.29 J kg{sup −1} for La{sub 0.5}Pr{sub 0.3}Ba{sub 0.2}Mn{sub 0.9}Ti{sub 0.1}O{sub 3} sample which will be an interesting compound for application materials. Also, an agreement was found between the magnetic entropy change values calculated by Landau theory and those obtained using Maxwell relation above T{sub C} and a difference below it, for a magnetic field of 2 T.
This work presents a novel approach based on the nitrate decomposition method for the preparation the oxygen-deficient LaBaCaCu{sub 3}O{sub y} (La1113) compound. The XRD results reveal the presence of the triple perovskite structure LaBaCaCu{sub 3}O{sub y} as a dominant phase crystallizing in the tetragonal system with the space group P4/mmm. The SEM observation shows a low porosity and EDAX data indicates the presence of the basic elements of the phase. The superconducting character of the compound is confirmed by AC susceptibility measurements with T{sub c} = 63 K even if the samples are not treated under oxygen atmosphere.
The confirmation of ferromagnetism at low temperature in a low-doped manganites system is always debatable. It is for the first time, electrical, magnetic, and thermal properties have been measured for manganites single crystal of La{sub 0.88}Ca{sub 0.12}MnO{sub 3} by using a floating-zone method. The electrical resistivity shows a perceptible change of resistance at a low temperature which can be viewed as a signature of the ferromagnetic phase. The ferromagnetic phase of the investigated La{sub 0.88}Ca{sub 0.12}MnO{sub 3} single crystal with Curie temperature of T{sub C} = 120 K which is in closed agreement with ac-susceptibility measurement. An analysis of the specific heat suggests the transition peak (T{sub P}) coincides with the T{sub C} and attains 1.2 J mol{sup −1} K at 116 K. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) were found to be 69% and 10% respectively, which expands its subtle potential for applications in spintronics and thermistor.
A complex study of the electron transport and magnetic characteristics of epitaxial manganite films La{sub 0.7}Ba{sub 0.3}MnO{sub 3} (LBMO) was carried out under conditions of the crystal structure tension caused by a mismatch between the parameters of the LBMO crystal and the substrate. The epitaxial thin films with the thickness 40–100 nm were grown by pulsed laser deposition at T = 700–800 °C in pure oxygen pressure 0.3–1 mbar. The substrates (110) NGO, (001) STO, (001) LAO, and (001) LSAT were used. By comparison of the lattice parameter of LBMO targets with substrate’s one, the lattice mismatches were derived. We used substrates in which the lattice parameter was less than for the LBMO crystal one. It is shown that the temperature dependence of the film resistance in the low-temperature region does not depend on the film stress and is in good agreement with the calculation that takes into account the interaction of carriers with magnetic excitations in the presence of strongly correlated electron states. A nonmonotonic temperature dependence of the resistance of an LBMO film deposited on ferroelectric crystals PMN-PT that was observed. This feature is typical for manganites, and indicating the presence of ferromagnetism in the system was observed.
The original version of this article unfortunately contained a mistake in Fig. 4(b) and Fig. 5(b). On the Y-axis, (states/eV) should be F(w)(states/eV). The original article has been corrected.
We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa{sub 2}Cu{sub 3}O{sub 7−y} (YBCO) and the colossal magnetoresistive manganite LaMnO{sub 3} (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below T{sub Curie}∼160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias (V∼1–2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5-nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a ∼ 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current.
Superconducting properties of LaSn{sub 3} were calculated at ambient and applied positive hydrostatic pressure. The lattice structure of LaSn{sub 3} remained stable at ambient and all applied positive hydrostatic pressures due to the positive frequency of phonon dispersion plots for all modes of vibrations. The electron-phonon coupling constant (λ{sub ep}) and superconducting transition temperature (T{sub c}) show an almost linear decrease with positive hydrostatic pressure. The majority of electron‑electron interaction is mediated by acoustic modes of vibration in comparison to optical modes of vibrations.
The key feature of parent cuprates of the La{sub 2}CuO{sub 4} type, in addition to their high ionic polarizability and closeness to polarization catastrophe, is identified as their instability against charge transfer that is accompanied by the formation of a system of metastable dipole-active Mott–Hubbard excitons, i.e., electron–hole (EH) dimers. This feature determines the behavior of cuprates upon nonisovalent substitution. Within the simplest model equivalent to a system of composite bosons, nonisovalent substitution shifts the phase equilibrium toward condensation of EH dimers and the formation of inhomogeneous EH liquid. To describe the electronic state of doped cuprates effectively, we propose to use the pseudospin S = 1 formalism. It enables us to treat cardinally new charged states such as Anderson’s RVB phases. Recombination of EH dimers at a critically low energy of local and nonlocal correlations drives the system into the state of a Fermi liquid.
Mathematical aspects of thermal diffusivity measurements are reviewed and applied to develop an experimental setup at JPL. Certain approximations commonly appearing in the literature are examined in some detail and rejected based upon sensitive slope variations having significant impact on the results. The final mathematical formulation used was one developed by Parker et al. (1961), which evaluated the diffusivity in a way that could be simply evaluated by examining an oscilloscope trace. A computer algorithm was written to examine solution sensitivity to the number of terms taken in the infinite series. The mathematical technique is being used at JPL to evaluate diffusivities of graphite, Boron Carbon and Lanthanum Sulphur compounds in the temperature range of 300 K to 1200 K.
Cesium cerium bromide (Cs2CeBr5) and potassium cerium bromide (K2CeBr5) are new scintillator materials for X-ray and gamma ray detector applications. Recently halide scintillator materials, such as Ce doped lanthanum bromide has been proved to be very important material for the same purpose. These materials are highly hygroscopic; a search for high light yield non-hygroscopic materials was highly desirable to advance the scintillator technology. In this paper, we are reporting the crystal growth of novel scintillator materials, cesium cerium bromide (Cs2CeBr5) and potassium cerium bromide (K2CeBr5). Crystals were successfully grown from the melt using the vertical Bridgman-Stockbarger technique, in a comparison with the high performance LaBr3 or LaCl3 crystals, cerium based alkali halides crystals, (Cs2CeBr5) and (K2CeBr5) have similar scintillation properties, while being much less hygroscopic. Furthermore, cesium based compounds will not suffer from the self-activity present in potassium and lanthanum compounds. However the Cs2CeBr5 crystals did not grow properly probably due to non-congruent melting or to some phase transition during cooling. Keywords." Scintillator materials; Ce3+; Energy resolution; Light yield; K2CeBr5