Showing papers on "Valency published in 1988"
TL;DR: In this paper, the authors performed band calculatons for high T c related oxides, La 2 CuO 4, YBa 2 Cu 3 O y (y =6 or 7), La 2 CaCu 2 O 6, CuO, and also NiO with the fullpotential linear augmented plane wave method in order to derive information about the characteristic aspects of these materials.
Abstract: We have performed band calculatons for the high- T c related oxides, La 2 CuO 4 , YBa 2 Cu 3 O y ( y =6 or 7), La 2 CaCu 2 O 6 , CuO, and also NiO with the full-potential linear augmented plane wave method in order to derive information about the characteristic aspects of these materials. We pay particular attention to the energy separation between the oxygen p and the copper d levels, the assignment of a p orbital for the extra hole accommodation, the significance of the p - p hopping, the occupancy in the two-dimensional Cu-O bands, and the Cu valency.
63 citations
TL;DR: In this paper, the X-ray absorption spectra of the Cu K-edge have been obtained for a high-T c superconductor YBa 2 Cu 3 O 7−y by in-situ high temperature measurements between room temperature and 600 °C and for quenched samples prepared by rapid cooling from various temperatures up to 880 °C.
32 citations
TL;DR: A partial review of high energy spectroscopic studies of the new superconductors is given in this paper, where the authors summarize the evidence on the ground state electronic configuration of these materials, the "valency" of Cu, the strength of elecrton-electron correlation, and the nature of the hole states which apparently lead to superconductivity.
Abstract: A partial review of high energy spectroscopic studies of the new superconductors is given. We attempt to summarize the evidence on the ground state electronic configuration of these materials, the "valency" of Cu, the strength of elecrton-electron correlation, and the nature of the hole states which apparently lead to superconductivity.
27 citations
TL;DR: In this paper, the authors illustrate how bond order and valency can be retrieved from MO calculations and give examples for several simple molecules, such as polycyclic molecules, for instance.
Abstract: These authors illustrate how bond order and valency can be "retrieved" from MO calculations and give examples for several simple molecules.
25 citations
TL;DR: The general criteria for a molecular orbital quantity to serve as a successful Walsh ordinate to give correct qualitative predictions of molecular shape are formulated in this paper, where the general criteria are derived from the general requirements for a successful ordination.
Abstract: The general criteria for a molecular orbital quantity to serve as a successful Walsh ordinate to give correct qualitative predictions of molecular shape are formulated.
24 citations
01 Jan 1988
12 citations
TL;DR: In spite of the steric hindrance effect that is prevalent with multivalent antigens, the antigenic valency is a constant parameter and not a variable influenced by the ratio of antibody to antigen.
12 citations
TL;DR: In this article, a comparative XPS study of the superconductor YBCO and its non-superconducting tetragonal modification is presented towards the better understanding of the valency of Cu in these systems.
Abstract: A comparative XPS study of the superconductor YBCO and its non-superconducting tetragonal modification is presented towards the better understanding of the valency of Cu in these systems.
11 citations
TL;DR: In this paper, a home spectrometer using a conventional X-ray tube and a position sensitiv detector (silicon diode array) in energy dispersive mode is presented.
Abstract: The measurement of LIII-absorption edges is known to be an important tool for obtaining information about the 4f-occupation number in intermediate valent rare earth compounds. It is of great interest to determine the temperature dependence of the valency in these systems. Therefore we developed a home spectrometer using a conventional X-ray tube and a position sensitiv detector (silicon diode array) in energy dispersive mode. A helium cryostat allows measurements between 4 and 300 K. We present data of intermediate valent Sm- and Yb-systems.
9 citations
TL;DR: In this paper, the role of oxygen deficiency and carrier concentration on the superconducting properties of Y1Ba2Cu3O7−δ (Tc=93K) was investigated.
Abstract: A systematic study has been carried out on thesame sample in order to determine the role of oxygen deficiency and carrier concentration on the superconducting properties of Y1Ba2Cu3O7−δ (Tc=93K). Specifically we have measured the Hall coefficient, electrical resitivity, acsusceptibility and x-ray diffraction on this sample after successive steps in which the oxygen deficiency was controlled and determined from thermogravimetry. From our Hall effect data, analysed in terms of effective single-band carriers(R=−1/ne), we find that the normal state carrier density decreases with oxygen depletion and that the number of free carriers extrapolate to almost zero forδ=0.5. We note that for 0<δ<0.5 the average formal Cu valency must be larger than +2 and thatδ=0.5 is exactly the degree of oxygen depletion at which the average Cu valency is equal to +2. In addition, it is interesting to point out that our Hall data combined with an appropriate resistivity for a dense material suggest a rather short mean-free path (<10A˚) On the other hand, the temperature dependence of resistivity as analysed by Gurwitch et al. (1), would imply that the mean-free path is substantially longer. We believe that this appearent contradiction is due to the estimation of the effective mass of the carriers in these structures.
9 citations
TL;DR: In this article, the distribution of cations de haute valence dans les structures of type spinelle is discussed, using the regle electrostatique de Pauling.
Abstract: Article de synthese concernant la distribution des cations de haute valence dans les structures de type spinelle. Application de la regle electrostatique de Pauling a quelques structures
TL;DR: In this article, the question of rare-earth valency in Y 1-x M x Ba 2 Cu 3 O 7−δ compounds (with M = Ce, Pr, Tb) is addressed by x-ray absorption (XA) near-edge structure (XANES) studies at the RE-M 4.5 and -L 2,3 thresholds.
Abstract: The question of rare-earth (RE) valency in Y 1-x M x Ba 2 Cu 3 O 7−δ compounds (with M = Ce, Pr, Tb) is addressed by x-ray absorption (XA) near-edge structure (XANES) studies at the RE-M 4.5 and -L 2,3 thresholds. While Pr is found to be essentially trivalent for all x, the' related Ce systems are characterized by tetravalent Ce; Tb is found to be trivalent for small x, but tetravalent for x = 1. Possible mechanisms for T c suppression are discussed.
TL;DR: In this paper, the X-ray absorption near-edge structure (XANES) and extended Xray absorption fine structure (EXAFS) techniques were used to analyze high-Tc YBa2Cu3Ox.
Abstract: The a Cu valency and local structure in high-Tc YBa2Cu3Ox have been analyzed by X-ray absorption near-edge structure (XANES) and by extended X-ray absorption fine structure (EXAFS) techniques. The Cu valency is predominantly divalent. The evidence for trivalent Cu has not been observed. The radial distribution function around Cu ions indicates that an average of 4.1 oxygen atoms are present at 1.915 A.
TL;DR: The Na content of the fast ionic conductor Na-β-alumina can be fully replaced by ion exchange with a wide variety of divalent ions as mentioned in this paper, and the structure and optical properties of the system are greatly affected by both composition and thermal treatment, which determine the balance between the configurational entropy, site preference and Coulombic repulsions of the cations in the conduction planes.
TL;DR: The crystal structures and magnetic properties of superconducting substance in YBa2(Cu1-xMx)3Oy, where M is a 3 d transition element and x=0, 0.01,0.03, 0,10, were investigated as discussed by the authors.
Abstract: The crystal structures and magnetic characteristics of the superconducting substance in YBa2(Cu1-xMx)3Oy, where M is 3 dtransition element and x=0, 0.01, 0.03, 0.10, were investigated. Substitution of Ni and Zn left the orthorhombic structure at x=0.10, whereas substitution of Fe and Co induced an orthorhombic to tetragonal transition at x=0.03. The valency of substituted Co ion was divalence, whereas the valency of other substituted magnetic ions was not determined for certain.
Patent•
03 Feb 1988
TL;DR: In this paper, a fluorine carboxylic ester membrane is used as an ion exchange membrane to change the valency of an aq. metal ion soln. by using fluorine anion exchange membrane having a specified structure.
Abstract: PURPOSE:To efficiently change and control the valency of an aq. metal ion soln. by using a fluorine anion-exchange membrane having a specified structure produced by applying treatment with an acid or a base. CONSTITUTION:The valency of an aq. soln. of a metal ion capable of forming plural oxidation states is changed and controlled by anion-exchange membrane electrolysis. A membrane formed from a copolymer consisting of a repeating unit shown by the formula is treated with an acid or a base, and an anion- exchange group is introduced into the copolymer to obtain a fluorine carboxylic ester membrane which is used as the anion-exchange membrane in this case. In the formula, X is F or CF2, (l) is 0 or 1-5, (m) is 0 or 1, (n) is 1-5, p/q is 4-16, and R is an alkyl. Since the anion-exchange membrane has excellent durability and a metal ion is not leaked, the membrane is applicable to various processes, and the valency of the metal ion can be efficiently changed and controlled.
TL;DR: In this article, a newly discovered mechanism for superconductivity which seemingly explains the attraction responsible for Cooper pairing is presented, and the mechanism concerns charge fluctuations in parallel, neighboring planes, the interaction between two such fluctuations is a calculable function.
Abstract: The author discusses present knowledge of the valency of the various ions in high-T/sub c/ superconductors. He reports on a newly discovered mechanism for superconductivity which seemingly explains the attraction responsible for Cooper pairing. The mechanism concerns charge fluctuations in parallel, neighboring planes. The interaction between two such fluctuations is a calculable function. This mechanism could well explain the higher T/sub c/'s of the present generation ceramic superconductors. Being unrelated to any specific properties of copper oxide, beyond the specific value of {kappa}/sub F/, it should also be applicable to a variety of non-ceramic materials,of which artificially layered semiconductors and intercalation compounds are two families.
Patent•
25 Nov 1988
TL;DR: In this paper, the authors proposed to increase the mechanical strength by incorporating a metal atom in the amt smaller than the stoichiometric amt. in the specified perovskite metal oxide for electroceramics.
Abstract: PURPOSE:To increase the mechanical strength, such as transverse strength, etc. by incorporating a metal atom in the amt. smaller than the stoichiometric amt. in the specified perovskite metal oxide for electroceramics. CONSTITUTION:In the perovskite metal oxide shown by the formula, A(B, C)xDyO3, the metal element shown by B is incorporated in the amt. smaller than the stoichiometric amt. by 1-25atom.% to obtain the aimed metal oxide for electroceramics. In the formula, A is a bivalent metal element having 12 oxygen coordination number or >=2 kinds of metal elements incorporated in such ratio that the mean valency is controlled to two. In addition, C is a metal element having 6 oxygen coordination number, and D is a 4 valent metal element having 6 oxygen coordination number or >=2 kinds of metal elements incorporated in such ratio that the mean valency is controlled to four. Besides, the B element and C element are incorporated so that the mean valency of the elements is controlled to four, (x) is >=0.05, and the sum of (x) and (y) is 0.95-1.05.
TL;DR: The role of oxygen vacancies in high Tc superconductivity of Ba 2 YCu 3 O y (6.22 c) to low T c (50-60 K) states at the critical oxygen content y=6.7 is strongly related with the local structure and Cu valency as mentioned in this paper.
Abstract: The role of oxygen vacancies in high Tc superconductivity of Ba 2 YCu 3 O y (6.22 c (90 K) to low T c (50–60 K) states at the critical oxygen content y=6.7 is strongly related with the local structure and Cu valency. Extended x-ray absorption fine structure (EXAFS) results indicate that oxygen ordering in the O1-Cu1-O1 linear chain predominantly influences the structure along the c-axis and the Cu-0 vibrational properties of CuO 2 planes. The near-edge spectra indicate that Cu + species are formed at Cul sites below the critical oxygen content, suggesting that the presence of Cu d-hole on the O1-Cu1-O1 chain is essential for high T c (90 K) superconductivity.
TL;DR: In this article, the binding energy per valence electron of a simple metal is well described, in atomic units, experimentally and theoretically by the formula a+bz/4rc, where z is the valency, rc is the empty core radius, a approximately = 0.1 and, in all except the group 1A and 2A cases, 0.9
Abstract: It is shown that the binding energy per valence electron of a simple metal is well described, in atomic units, experimentally and theoretically by the formula a+bz/4rc. Here z is the valency, rc is the empty-core radius, a approximately=0.1 and, in all except the group 1A and 2A cases, 0.9
Patent•
12 Oct 1988
TL;DR: In this article, superconductive materials consisting of oxides of copper of mixed valency of the oxygen-deficient perovskite type of formula: La1+ epsilon Ba2-epsilon Cu3O8-y with -0.2
Abstract: Superconductive materials consisting of oxides of copper of mixed valency of the oxygen-deficient perovskite type of formula: La1+ epsilon Ba2- epsilon Cu3O8-y with -0.2
TL;DR: In this article, several extensions of a "minimal" model of Jahn-Teller systems are given and discussed, and it is found that a model which increases the softness of the defect surrounding (additonal collective T2g state in the Sm subspace of the system SmB6: Er3+) yields the strongest improvement of the calculated ESR results.
Abstract: Several extensions of our "minimal" model of valency-mixing Jahn-Teller systems are given and discussed. It is found that a model which increases the "softness" of the defect surrounding (additonal collective T2g state in the Sm subspace of the system SmB6: Er3+) yields the strongest improvement of the calculated ESR results. Good results are also found for a "double" Jahn-Teller model.
TL;DR: In this paper, a model has been proposed for the electronic structures in V2O5-MoO3 compounds, in which the valency d electrons are delocalized between the molybdenum and vanadium atoms.
Abstract: Measurements have been made on Mo Lβ2, 15 and V Kβ"β5 x-ray emission spectra for V2O5-MoO3 compounds. There is a relationship between the Mo Lβ2,15 characteristics and the population in the 4d-like molybdenum band. That 4d band for molybdenum in V2O5-MoO3 has an appreciable electron density, which decreases as the molybdenum concentration increases. A model has been proposed for the electronic structures in these compounds, in which the valency d electrons are delocalized between the molybdenum and vanadium atoms.
TL;DR: The general criteria for a molecular orbital quantity to serve as a successful Walsh ordinate to give correct qualitative predictions of molecular shape are formulated in this paper, where the general criteria are derived from the general requirements for a successful ordination.
Abstract: The general criteria for a molecular orbital quantity to serve as a successful Walsh ordinate to give correct qualitative predictions of molecular shape are formulated.
TL;DR: In this paper, the dependence on quark flavour of hyperfine mass separations is studied within the quark flavor number framework for the case of pseudoscalar and vector meson ground states.
Abstract: The dependence on quark flavour of hyperfine mass separations is studied within the quark flavour number framework for the case of pseudoscalar and vector meson ground states. It is shown that for mesonic partners with at least one beauty valency the flavour dependence with respect to the flavour of the remaining valency differs from the corresponding dependence for partners with at least one nonstrange or at least one strange valency. For partner mesons with at least one charmed valency the hyperfine splittings are almost independent of the other flavour.