Neutron Scattering study of Sr_2Cu_3O_4Cl_2

We report a neutron scattering study on the tetragonal compound Sr_2Cu_3O_4Cl_2, which has two-dimensional (2D) interpenetrating Cu_I and Cu_{II} subsystems, each forming a S=1/2 square lattice quantum Heisenberg antiferromagnet (SLQHA). The mean-field ground state is degenerate, since the inter-subsystem interactions are geometrically frustrated. Magnetic neutron scattering experiments show that quantum fluctuations lift the degeneracy and cause a 2D Ising ordering of the Cu_{II} subsystem. Due to quantum fluctuations a dramatic increase of the Cu_I out-of-plane spin-wave gap is also observed. The temperature dependence and the dispersion of the spin-wave energy are quantitatively explained by spin-wave calculations which include quantum fluctuations explicitly. The values for the nearest-neighbor superexchange interactions between the Cu_I and Cu_{II} ions and between the Cu_{II} ions are determined experimentally to be J_{I-II} = -10(2)meV and J_{II}= 10.5(5)meV, respectively. Due to its small exchange interaction, J_{II}, the 2D dispersion of the Cu_{II} SLQHA can be measured over the whole Brillouin zone with thermal neutrons, and a novel dispersion at the zone boundary, predicted by theory, is confirmed. The instantaneous magnetic correlation length of the Cu_{II} SLQHA is obtained up to a very high temperature, T/J_{II}\approx 0.75. This result is compared with several theoretical predictions as well as recent experiments on the S=1/2 SLQHA.Comment: Figures and equations are rearrange

Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit

We have investigated the lowest binding-energy electronic structure of the model cuprate Sr_2CuO_2Cl_2 using angle resolved photoemission spectroscopy (ARPES). Our data from about 80 cleavages of Sr_2CuO_2Cl_2 single crystals give a comprehensive, self-consistent picture of the nature of the first electron-removal state in this model undoped CuO_2-plane cuprate. Firstly, we show a strong dependence on the polarization of the excitation light which is understandable in the context of the matrix element governing the photoemission process, which gives a state with the symmetry of a Zhang-Rice singlet. Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice singlet on the exciting photon-energy is shown to be consistent with interference effects connected with the periodicity of the crystal structure in the crystallographic c-direction. Thirdly, we measured the dispersion of the first electron-removal states along G->(pi,pi) and G->(pi,0), the latter being controversial in the literature, and have shown that the data are best fitted using an extended t-J-model, and extract the relevant model parameters. An analysis of the spectral weight of the first ionization states for different excitation energies within the approach used by Leung et al. (Phys. Rev. B56, 6320 (1997)) results in a strongly photon-energy dependent ratio between the coherent and incoherent spectral weight. The possible reasons for this observation and its physical implications are discussed.Comment: 10 pages, 8 figure

Expanding frontiers in materials chemistry and physics with multiple anions

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials

EFFECT OF REPLACING TREATED AND UNTREATED CORN IMPURITIES WITH UREA INSTEAD OF WHEAT BRAN ON PRODUCTIVE PERFORMANCE OF AWASSI LAMBS

The study was conducted to study the effect of replacing different levels of treated and untreated corn impurities with urea instead of wheat bran on productive performance of Awassi lambs. Wheat bran were replaced by five levels of treated and untreated corn impurities as: 44:0%, 32:11%, 20:22%, 10:32% and 0:39% bran: impurities in a 2×5 factorial experiment. Concentrated fed at 3% of live body weight as dry matter basis, while alfalfa hay was offered ad libitum. Forty Awassi lambs were used, with an initial weight of 27.45 ± 2.16 kg and 4-5 months old. All lambs were fed individually feeding for 70 days, preceded by 14 days as adaptation period. Results showed a non-significant superiority in dry matter and nutrients intake by increasing corn impurities and a highly significant increased (p<0.01) in ether extract and ash intake (g/day), with superiority of digestibility (P<0.05) of organic matter% (OM) and crude protein% (CP), feed efficiency, daily gain (g/ day) and total weight gain (kg) for feeding 30% of corn impurities treated with urea (T9). In conclusion, it is possible to use corn impurities instead of wheat bran, preferably treated with urea to increase crude protein content, degraded crude fibers and improved nutritional values

INFLUENCE OF FEEDING CORN IMPURITIES ON RUMEN BACTERIA AND FERMENTATION CHARACTERISTICS OF SHEEP

This study was aimed to determine the effect of replacing treated and untreated corn impurities with urea instead of wheat bran on rumen bacteria and fermentation of Awassi lambs. Five levels of treated and untreated corn impurities as 44:0%, 32:11%, 20:22%, 10:32% and 0:39% bran:impurities in a 2×5 factorial experiment/ Completely Randomized Design using forty lambs with an initial weight of 27.45 ± 2.16kg and 4-5 months old. Individual feeding was used for 70 days and rumen fluid was sampled at 0, 3, 6h after morning feeding. Results showed an increasing (p<0.05) rumen pH at zero time especially corn impurities treated with urea and increasing (p<0.05) rumen ammonia at zero time and 3h after feeding with highly significant (p<0.01) increased at 6h, and superiority increased of volatile fatty acids (VFA's) for urea treated corn impurities (P<0.05) at zero time and after 3h of feeding, similar results for rumen bacterial count at zero time, 3h and 6h after morning feeding for two dilutions × 107 and × 109 Cfu/ml for impurities treated with urea. In conclusion, it is possible to use corn impurities instead of wheat bran, preferably treated with urea for positive increase rumen fermentation and total bacterial count in sheep

Electronic transport in highly conducting Si-doped ZnO thin films prepared by pulsed laser deposition

Highly conducting (ρ = 3.9 × 10-4 Ωcm) and transparent (83%) polycrystalline Si-doped ZnO (SiZO) thin films have been deposited onto borosilicate glass substrates by pulsed laser deposition from (ZnO)1-x(SiO2)x (0 ≤ x ≤ 0.05) ceramic targets prepared using a sol-gel technique. Along with their structural, chemical, and optical properties, the electronic transport within these SiZO samples has been investigated as a function of silicon doping level and temperature. Measurements made between 80 and 350 K reveal an almost temperature-independent carrier concentration consistent with degenerate metallic conduction in all of these samples. The temperature-dependent Hall mobility has been modeled by considering the varying contribution of grain boundary and electron-phonon scattering in samples with different nominal silicon concentrations

Superconducting Sr_2-xA_xCuO₂F_2+δ (A = Ca, Ba):Synthetic pathways and associated structural rearrangements

The low-temperature fluorination of a range of insulating alkaline earth cuprates Sr2-xAxCuO3 (A = Ca (0 ≤ x ≤ 2); A = Ba (0 ≤ x ≤ 0.6)) can result in superconducting oxide fluorides Sr2-xAxCuO2F2+δ. In contrast, conventional high-temperature solid-state reactions produce thermodynamically more stable mixtures of oxides and fluorides. Various soft-chemistry fluorination pathways (utilizing F2 gas, NH4F, MF2 [M = Cu, Zn, Ni, Ag]) are compared with respect to their efficacy and mechanisms. Attention is also focused on the structural features of the mixed-oxide precursor and the final-oxide fluorides to highlight the remarkable structural rearrangements that occur during the low-temperature fluorination. The effects of fluorination of other Sr-Cu-O systems are used to identify the structural requirements of the precursor oxide in order to achieve such transformations. © 1998 Academic Press

X-ray emission, photoelectron spectra, and electronic structure of Sr2CuO2F2+ delta.

The electronic structure of the high-Tc superconductor Sr2CuO2F2+ has been investigated by means of x-ray-emission spectroscopy (O K, Cu L F K), x-ray-photoelectron spectroscopy, and band-structure calculations using the full-potential linear muffin-tin orbital method. The local environment of the F atoms and the valence state of the Cu atoms in Sr2CuO2F2+ are discussed. On the basis of the x-ray-photoelectron and x-ray-emission spectra it is concluded that the F atoms preferentially bond to Sr atoms in this compound. © 1995 The American Physical Society