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Showing papers on "Valency published in 1989"


Journal ArticleDOI
TL;DR: In this paper, it was suggested that molecules containing cerium ions with a formal valency +4 may form a ground state resembling a Kondo singlet, and the experimental consequences for these systems are discussed.
Abstract: It is suggested that molecules containing cerium ions with a formal valency +4 may form a ground state resembling a Kondo singlet. This is demonstrated explicitly by choosing cerocene as an example. Experimental consequences for these systems are discussed.

49 citations


Journal ArticleDOI
TL;DR: Finite digrahs Г with a group G of automorphisms acting transitively on the set of s-arcs, for some s ⩾ 2, are investigated and an infinite family of finite digraphs of valency v which are s- Arc transitive but not (s + 1)-arc transitive are constructed.
Abstract: Finite digrahs Г with a group G of automorphisms acting transitively on the set of s-arcs, for some s ⩾ 2, are investigated. For each valency v and each s ⩾ 2 an infinite family of finite digraphs of valency v which are s-arc transitive but not (s + 1)-arc transitive are constructed. These examples are the result of a general construction given in the paper. Several classification results are proved and the case of G primitive on vertices is discussed.

48 citations


Journal ArticleDOI
TL;DR: The europium valency in hexagonal EuPtP, as examined by LIII-x-ray absorption and Moessbauer experiments, is a function of temperature and changes from 2.16 at 295 K to 2.40 at 4 K as mentioned in this paper.
Abstract: The europium valency in hexagonal EuPtP, as examined byLIII-x-ray absorption and Moessbauer experiments, is a function of temperature and changes from 2.16 at 295 K to 2.40 at 4 K. In the region of the strongest temperature dependence of the valency, the compound undergoes two first order phase transitions atT1=235 K andT2=190 K, characterized by discontinuities in the lattice constants and in the magnetic susceptibility. In the europium Moessbauer spectra, several temperature dependent absorption lines were found, indicating a complex europium valency behaviour. Furthermore, we observe antiferromagnetic order at 8.6 K.

36 citations


Journal ArticleDOI
TL;DR: In this article, electron energy-loss spectroscopy on Nd2−xCexCuO4 was performed and the valency of Ce was found to be close to 3.4.
Abstract: We present results from electron energy-loss spectroscopy on Nd2−xCexCuO4. There is no clear evidence for Cu1+ but for holes at the oxygen sites. The valency of Ce is found to be close to 3.4. Thus our results do not corroboraten-type superconductivity in this compound.

33 citations


PatentDOI
Barri Sami Ali Ibrahim1
20 Jul 1989-Zeolites
TL;DR: The SUZ-2 as discussed by the authors is a crystalline material having, in the dehydrated form, the empirical formula: m(m.sub.z O.sub 2/a O):X.sub 1.xz/2 :.y YO.

24 citations


Journal ArticleDOI
TL;DR: In this paper, a complex system containing both Ca 2+ and Sr 2+, La 1.6 (Sr x Ca 1-x ) 1.4 Cu 2 O y, is investigated in terms of crystal structure, copper valency and electrical conductivity.

22 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of nonsingular transformation of the AO basis set on MO calculations of valency has been studied, taking as examples a number of molecules with varying degrees of ionicity and using a variety of basis sets.

22 citations



Journal ArticleDOI
TL;DR: Distance-regular graphs with certain specific intersection arrays are investigated and it is shown that the diameter d of the graph is bounded by a function depending only on t and the valency k if k ⩾ 3.
Abstract: Distance-regular graphs with certain specific intersection arrays are investigated. In particular, it is shown that if the columns of the intersection array are all of the form t (*, 0, k ), t (1, a , k - a - 1), t ( k - a - 1, a , 1) and t ( k - e , e , *) except for t intermediate columns, then the diameter d of the graph is bounded by a function depending only on t and the valency k if k ⩾ 3.

20 citations


Journal ArticleDOI
TL;DR: In this paper, photoelectron spectroscopy studies on a molecular Cu (III) complex are compared with those of the perovskite type high Tc superconductor YBa2Cu3O7.

18 citations



Journal ArticleDOI
TL;DR: In this article, the effects of misdirected valency are primarily monitored through Lt, and especially Lt, parameters, and detailed ligand field analyses of both transition energies and intensity distributions in the “d-d” spectra of the five-coordinate Schiff-base complexes [bis(salicylidine-y-aminopropyl)aminato]nickel( 11) and
Abstract: Cellular ligand-field energies in local C, pseudosymmetry for a ligation in a metal complex characterized by bent bonding or other forms of misdirected valency require the off-diagonal cellular ligand-field (CLF) parameter The parametrization scheme required for the corresponding CLF intensity model is derived. It is shown that the effects of misdirected valency are primarily (and probably sufficiently) monitored through Lt, and especially Lt, parameters. Detailed ligand-field analyses of both transition energies and intensity distributions in the “d-d” spectra of the five-coordinate Schiff-base complexes [bis(salicylidine-y-aminopropyl)aminato]nickel( 11) and [ bis(salicylidene-y-aminopropyl)methylaminato]nickel( 11) are described. Discussions of optimal e and f parameter sets together furnish commentary upon the polarizations and lateral spreads of the electron distributions within the coordination bonds of these chromophores.

Journal ArticleDOI
TL;DR: In this article, the formation of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O superconducting system was investigated using X-ray photoemission spectroscopy (XPS) measurements.
Abstract: X-ray photoemission spectroscopy (XPS) measurements were carried out to investigate the changes in the Cu ion valency through the formation of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O superconducting system. The Cu2+ composition increased rapidly in the initial stages of sintering and became saturated, whereas the Cu+ and Cu3+ compositions showed a systematic change, within a certain sintering time, dependent on the sintering temperature. It was found that these changes in the Cu ion valency reflect the structural change in the formation of the high-Tc phase in this system.

Journal ArticleDOI
TL;DR: In this article, the electronic densities of states of YBa2Cu3O7-y with y=0.25, 0.125, 0, -0.125 have been calculated by the recursion method.
Abstract: The electronic densities of states of YBa2Cu3O7-y with y=0.25, 0.125, 0, -0.125 have been calculated by the recursion method. The authors have discussed the influence of the variation in O vacancies on the electronic structure and show that O vacancies can only exist in Cu-O chains. Their results show the atomic-like localised character of Cu 3d states and large O-metal covalency in this system. The valency of the Cu atoms is discussed and possible electronic configurations of Cu are proposed from an energy point of view. The most probable valency of O is -1 so that there is a hole-conducting mechanism in the Y-Ba-Cu-O system.

Journal ArticleDOI
TL;DR: In this article, the infrared spectra of vacuum-evaporated MoO3-In2O3 thin films are reported for a series of films of varying compositions within the spectral range 4000 to 400 cm−1.
Abstract: The infrared absorption spectra of vacuum-evaporated MoO3-In2O3 thin films are reported for a series of films of varying compositions within the spectral range 4000 to 400 cm−1 and interpreted in relation to the spectrum of the pure MoO3 films. The affects of changes in composition, film thickness, substrate deposition temperature and annealing on the absorption bands are observed. In some cases a shift in band frequency is also observed. The gradual increase in ordering and decrease in valency state with increase of annealing temperature is observed in the infrared curves. Some new peaks appear which reveal the presence of a lower valency state in MoO3. The shift in band frequency may be attributed to the incorporation of Mo(VI) ions in the indium interstitial positions.

Journal ArticleDOI
TL;DR: The transition copper valency in the Y-Ba-Cu-O superconductive system was studied with respect to its dependence on the sample processing, doping, the heating and cooling conditions, and on the atmosphere as discussed by the authors.


Journal ArticleDOI
TL;DR: In this paper, the volume behavior of cerium monoxide (CeO) is studied as a function of pressure and the authors present the fully selfconsistent band structure of CeO for four different values of lattice constant corresponding to four different pressures, using the linearised augmented plane-wave method.
Abstract: The volume behaviour of cerium monoxide (CeO) is interesting as a function of pressure. The volume decreases rapidly up to 3 GPa and decreases more slowly above 3 GPa. The authors present the fully self-consistent band structure of CeO for four different values of lattice constant corresponding to four different pressures, using the linearised augmented plane-wave method. The local density formulation has been assumed for the exchange and correlation part of the potential. From the band-structure results, they have calculated the valency of Ce in CeO. The calculated valency increases from 3.0 to 3.26 with increase in pressure. From the band-structure results, the density of states, the coefficient of linear specific heat and the optical absorption spectra have been calculated.

Journal ArticleDOI
TL;DR: In this paper, a superconducting single-phase Bi 2 Sr 2 Ca 1 Cu 2 O 8 has been investigated using X-ray photoelectron spectroscopy and the binding energy of 158.3 eV for the Bi 4f 7 2 level indicates the presence of bismuth in a valency state lower than + 3.

Journal ArticleDOI
TL;DR: In this paper, the local electronic structure of the high-Tc superconductors YBa2Cu3O7−δ and Nd2−xCexCuO4−ε 4−ε is probed by soft x-ray absorption spectroscopy at the Cu LII,III, O K, Ce MIV,V,V and nd MIV-V thresholds, and the near edge structures provide information on the partial unoccupied density of states above EF as well as on valency and covalency of the constituent elements.
Abstract: The local electronic structure of the high-Tc superconductors YBa2Cu3O7−δ and Nd2−xCexCuO4−δ is probed by soft x-ray absorption spectroscopy at the Cu LII,III, O K, Ce MIV,V, and Nd MIV,V thresholds. The near-edge structures provide information on the partial unoccupied density of states above EF as well as on valency and covalency of the constituent elements.







DOI
01 Feb 1989
TL;DR: In this article, a numerical correlation between quantum-chemically calculated bond valency and experimental heat of atomisation of molecules is reported, which is a reliable measure of bond multiplicity in a variety of molecules including cases where these are ambiguous classically.
Abstract: A numerical correlation between quantum-chemically calculated bond valency and experimental heat of atomisation of molecules is reported. It is shown that bond valency is a reliable measure of bond multiplicity in a variety of molecules including cases where these are ambiguous classically.

Journal ArticleDOI
TL;DR: In this article, the search for high Tc superconductors in Pb Sr Y,Ca Cu O system has been carried out based on crystal considerations as well as formal valency relationships.
Abstract: The search for high Tc superconductors in Pb Sr Y,Ca Cu O system has been carried out based on crystal considerations as well as formal valency relationships. The four perovskite-like phases were detected in samples with different compositions. Superconducting resistive anomalies were detected in some samples at about 80 K, however it was not clear what phase was really superconducting one.

Book ChapterDOI
01 Apr 1989
TL;DR: In this paper, the ground state of high TC cuprates is primarily described in terms of mixed valency between 3d9 and 3d10 related configurations, with very little Cu3+(3d8) configuration.
Abstract: Employing electron spectroscopic techniques, we show that the ground state of these high TC cuprates is primarily described in terms of mixed valency between 3d9 and 3d10-related configurations, with very little Cu3+(3d8) configuration. Temperature dependent changes in the spectral features are interpreted in terms of formation of dimerized hole species in primarily oxygen p-derived band, while Cu concomitantly assumes a larger proportion of 3d10 related configuration. It is also shown that the formation of these dimerized hole species leads to a drastic decrease in the frequency dependent surface resistivity of the samples.