Showing papers on "Valency published in 1991"
01 Jan 1991
TL;DR: In this paper, the authors propose a coupling model of Mixed Valence Line Shapes (MVL) for one-and two-electron mixed-valence systems, based on the PKS and MO models for One-and Two-Electron Systems.
Abstract: Mixed Valency Systems: Retrospect And Prospect.- Vibronic Coupling Models Of Mixed Valency: Relation Of The PKS And MO Models For One- And Two-Electron Systems.- Electric Field Perturbation Of Electronic (Vibronic) Absorption Envelopes: Application To Characterization Of Mixed Valence States.- Solvent And Temperature Effects In Mixed Valence Chemistry.- Electron Transfer In Mixed Valence Complexes In The Solid State.- Photoredox Chemistry Of Two-Electron Mixed Valence Systems.- How To Design Fast Two-Electron Transfer Reagents: 37-Electron Mixed Valence Fe(I)Fe(II)-Bisandwiches As Key Intermediates.- Magnetic And Optical Phenomena In Biological Iron-Sulfur Mixed Valence Complexes And Their Chemical Models. A Theoretical Approach.- Mixed Valency In Multinuclear Manganese Enzymes And Clusters.- Mixed Valence Iron And Chromium Fluorides. Bronzes And Related Compounds. Chemistry, Structure And Magnetism.- Mixed Valency Minerals: Influences Of Crystal Structures On Optical And Mossbauer Spectra.- Valency Disproportionation In Inorganic Solids.- Superconductivity By Local Pairs (Bipolarons) In Doped Metal Oxide Semiconductors.- A Comparison Between Conducting C.T. Crystalline Salts And L.B. Films.- Optical Spectroscopic Probes Of Mixed Valence Systems.- Inelastic Neutron Scattering Studies Of Mixed Valency Systems.- Mossbauer Emission Spectroscopy Of Mixed Valency After Nuclear Decay In Iron Complexes.- Intramolecular Electron Transfer. Applications In Molecular Electronics.- Vibronic Coupling Models For Mixed Valence Line Shapes: Going Beyond The PKS Approach.- Mixed Valency Oligomers: Model Pathways For The Control Of Their Properties.- The Effects Of Second Order Vibronic Coupling On The Symmetric Dimer And Trimer.- Semiclassical Approach To The Vibronic Problem For The Creutz-Taube Ion.- A New Spin Hamiltonian For Mixed Valence Systems Including Transfer, Exchange And Exchange-Transfer Terms.- An Example Of The Influence Of The Ligand Held On The Electron Localisation: The Mixed Valence Ferrocene-Ferricinium.- A First Stable Organometallic Analogue [mer(OC)3(PiPr3)2W(?-pyrazine)W(PiPr3)2(CO)3]+ Of The Creutz-Taube Ion. Similarities And Differences.- Mixed Valence Manganese Carboxylates Of Various Nuclearities.- Spectroscopic Studies Of Spin State And Electron Delocalization In A Binuclear Mixed Valence Fe(II/III) Complex.- Bis(Phthalocyaninato) Lanthanide Sandwich Compounds Exhibiting Mixed Valence Ligands.- The Ruthenium Blues.- Optical And Related Properties Of Metal-Halide Chain Compounds: Bulk And Small Particles.- Dielectric Relaxometry: Manganate (VI)-(VII) In Solid And Solution States.- Electronic Instabilities Of Two-Dimensional Metals, K3Cu8S6 And Rb3Cu8S6.- Chemistry And Properties Of New Examples Of Mixed Valence Compounds, Based On Organic ? Donor Molecules And Polyoxometalate Ions.- Mixed Valency In The Organic-Inorganic Compounds (BEDT-TTF)6Cu2Br6 And (BEDT-TTF)6Cu2Cl2Br4.- Electrochemical Generation Of Mixed Valency Copper Complexes In Solution.- Endor Determination Of Proton Hyperfine Tensors As Local Probes Of The Delocalization Of The Spin Population In The 4 Iron - 4 Sulfur Cubanes.- Theory Descriptions Of Mixed Valency.- Electron Transfer Mechanisms, From Dimers To Infinite Solids.- Applications: Energy Storage And Molecular Electronics.- Biology: Models And Proteins.
144 citations
TL;DR: In this article, the authors found that FePS 3, VPS 3 and V 0.78 PS 3 crystals have electrical conductivity higher than 10 −5 S cm −1, while MnPS 3, NiPS3, and ZnPS 3 have conductivities lower than 10−9 S cm−1 at room temperature.
70 citations
TL;DR: An extension of the counterion-condensation theory of linear polyelectrolytes has been developed for the case of a system containing a mixture of counterions of different valency, i and j, and the results predicted are consistent, in the limiting cases of single species component, with those of the original CC theory.
38 citations
TL;DR: In this paper, the effects of different valency and amount of antimony ions on the resulting microstructures of ZnO varistors were studied, from the observation of scanning electron microscopy (SEM).
Abstract: The effects produced by different valency and amount of antimony ions on the resulting microstructures of ZnO varistors were studied. From the observation of scanning electron microscopy (SEM), the composition originally added with high valency of antimony ion had a larger grain size than that originally added with a low valency of antimony ion. Conversely, the composition originally added with a high valency of antimony ion possessed fewer intragrain particles than that originally added with a low valency of antimony ion. The spinel particle size and number of intragrain particles increased when the sintering temperature was raised. The compositions containing more antimony oxide can form more spinel phases, and result in an increase in grain growth kinetic exponent and activation energy as well as a decrease in grain size. These compositions have fewer intragrain particles and more spinel particles than those containing less antimony oxide.
15 citations
TL;DR: In this paper, a spectroelectrochemical study of [Ru2X9]n−, XCl, Br; n=1, 2, 3, 4 has been undertaken.
15 citations
TL;DR: In this paper, the electrical resistivities and IR spectra of new mixed cation (Cu/Li)-DCNQI systems were examined and a linear dependence on the charge of DCNQIf was shown to be consistent with the mixed valency of Cu (Cu+1.3).
Abstract: Electrical resistivities and IR spectra of new mixed cation (Cu/Li)-DCNQI systems were examined. (MeBr-DCNQI)2Cu1−xLix (0.25 < x < 0.5) remains in the metallic state down to 4 K. The stretching frequency of C=N(imine) of DCNQI shows a linear dependence on the charge of DCNQIf which is consistent with the mixed valency of Cu (Cu+1.3).
14 citations
TL;DR: In this paper, resistivity-dependent expressions for the direct force valency Zd are presented, starting from a recently proposed new theory for the driving force in electromigration, using these expressions a good description is found for the measured effective valency of hydrogen in the transition metals V, Nb and Ta.
Abstract: Resistivity-dependent expressions for the direct force valency Zd are presented, starting from a recently proposed new theory for the driving force in electromigration. Using these expressions a good description is found for the measured effective valency of hydrogen in the transition metals V, Nb and Ta. Fits based on a constant Zd which are at present available led to the values 1.1, 0.44 and 1.23 for Zd in the three hosts in question. These values are not understood yet. According to the new expressions, Zd ranges between the bare-charge value of unity and the completely screened value of zero, which are limiting values obtained in the high- and low-resistivity limits, respectively. While the available experimental data are not able to discriminate between the description with a constant Zd and the new one with a resistivity-dependent Zd, the latter can be considered as much more satisfactory. Regarding a long-standing controversy concerning the magnitude of the direct valency, it is concluded that the new theory in fact reconciles the two extremes involved.
14 citations
TL;DR: In this paper, the X-ray near-edge structure of LaCuO 3 has been studied around the copper K-edge at 8979 eV to confirm this Cu valency, using standard compounds for reference.
13 citations
Patent•
BP1
TL;DR: The SUZ-4 as mentioned in this paper is a crystalline material having, in the dehydrated form, the empirical formula: m(M.sub.z O.sub 2/a O): X.Sub.xz/2 : yYO, in which m is 0.5 to 1.5; X is a metal of valency x, selected from aluminium, boron, gallium zinc, iron and titanium.
Abstract: A crystalline material having, in the dehydrated form the empirical formula: m(M.sub.2/a O): X.sub.z O.sub.xz/2 : yYO.sub.2 (I) in which m is 0.5 to 1.5; M is a cation of valency a; X is a metal of valency x, selected from aluminium, boron, gallium zinc, iron and titanium; z is 2 when x is an odd number, an z is 1 when x is an even number; y is at least 5; and Y is silicon or germanium; and having, in the calcined hydrogen form, an X-ray diffraction pattern including significant peaks substantially as shown in table I herein. The material has been designated SUZ-4.
9 citations
TL;DR: In this paper, a covalent model instead of an ionic one is proposed and the valency of the Bi atoms at the unequivalent sites is close to +3.
Abstract: Potassium and lead substituted single and polycrystalline material was examined by X-ray diffraction, X-ray topography, nonresonant microwave absorption, UPS and XPS. A covalent model instead of an ionic one is proposed. We find no evidence for a mixed valency of Bi. The valency of the Bi atoms at the unequivalent sites is close to +3. No density of states at the Fermi level has been detected.
8 citations
TL;DR: An x-ray photoemisson study of (DMe-DCNQI) 2 Cu is reported in this paper, where the line-shape analysis reveals the mixed valency of Cu + and Cu 2+, and the Cu 2 + : Cu 2+) ratio is found to be ∼ 2 : 1.
Abstract: An x-ray photoemisson study of (DMe-DCNQI) 2 Cu is reported. The line-shape analysis reveals the mixed valency of Cu + and Cu 2+ , and the Cu 2+ : Cu 2+ ratio is found to be ∼ 2 : 1. This suggest that Cu is in a valance fluctuating state in the metallic state and, in other (DCNQI) 2 Cu compounds, a Cu + Cu 2+ charge-ordering takes place below the metal-insulator transition temperature.
TL;DR: In this paper, the optical properties of Y 1− x Pr x Ba 2 Cu 3 O 7−δ were investigated and it was shown that the free carriers disappear with increasing x.
Abstract: We investigated the optical properties of Y 1− x Pr x Ba 2 Cu 3 O 7−δ . We find that the free carriers disappear with increasing x . However, no fundamental changes in the interband transitions can be observed down to 50 meV, thus suggesting that no fundamental changes occur in the band structure. This fact, together with the behavior of the dielectric function, suggests that Pr is trivalent and the carriers are either localized or a gap smaller than 50 meV opens.
TL;DR: In this article, a charge self-consistent LCAO band structure (CSCBS) calculation was performed for orthorhombic YBa2Cu3O7 and tetragonal yBa2cu3O6 assuming ordered vacancy models.
Abstract: Charge self-consistent LCAO band structure (CSCBS) calculations are reported for orthorhombic YBa2Cu3O7 and tetragonal YBa2Cu3O6 assuming ordered vacancy models. The effective atomic charges are used to study the charge transfer. In YBa2Cu(1)1Cu(2)2O7, the two types of copper atoms have their energy bands almost overlapping with effective valency of each copper as 7/3 (or effective valency of each oxygen as approximately — 13/7), so that electron hopping can take place without any loss or gain of energy while in YBa2Cu(1)1Cu(2)2O6, Cu(1)1 is monovalent and Cu(2)2 are divalent with significant difference in their bands. Therefore, YBa2Cu3O7 should conduct much better compared to YBa2Cu3O6. This corroborates the experimental observations that YBa2Cu3O7 is a (super)conductor while YBa2Cu3O6 is not. The calculated effective charges and DOS support the above view.
01 Jan 1991
TL;DR: In this paper, the conductivities of mixed valent in both the organic and inorganic layers are shown to be O.6Scm-1 at 298K and are activated (0.165 and 0.087eV for T > ~230K; 0.03eV at T < 200K).
Abstract: The two compounds are shown to be mixed valent in both the organic and the inorganic layers. The conductivities are ~O.6Scm-1 at 298K and are activated (0.165 and 0.087eV for T > ~230K; 0.03eV for T < 200K). The magnetic properties are dominated by the copper(II) moments. The 3D ordering at ~10K in the case of the bromide indicates strong exchange interaction with the moments on the BEDT-TTF layers.
01 Jan 1991
01 Jan 1991
TL;DR: In this paper, a combination of experimental techniques is used to study the structural, optical and vibrational properties of antimony(m,v) halide salts, prototypes of class II mixed valency behaviour.
Abstract: A combination of experimental techniques is used to study the structural, optical and vibrational properties of antimony(m,v) halide salts, prototypes of class II mixed valency behaviour. The results together with simple lattice dynamics calculations lead to an estimate of an upper limit of the effective Hubbard-U for the antimony valency disproportionation. Inelastic neutron scattering is also used to study the phonon properties of the (Ba,K)(Pb,Bi,Sb)O3 series. Here the CDW instability is suppressed on doping, leading to delocalisation of the electrons and the appearance of superconductivity.
31 Dec 1991
01 Jan 1991
TL;DR: Themes evoked at the 1990 Crete meeting on mixed valency are briefly surveyed, with special reference to the progress made since the previous NATO conference on the subject in 1979 as discussed by the authors.
Abstract: Themes evoked at the 1990 Crete meeting on mixed valency are briefly surveyed, with special reference to the progress made since the previous NATO conference on the subject in 1979. Comments are made on the types of compound of current interest, the new techniques being applied and the theoretical advances.
01 Jan 1991
TL;DR: In this paper, the average valence of the metal ions and the chemical nature of the bridging ligand which joins two or more of them together are discussed, and a model Hamiltonian which incorporates such effects is presented.
Abstract: Two possible means of control ofthe properties of mixed-valence oligomers are discussed: the average valence of the metal ions and the chemical nature of the bridging ligand which join two or more of them together. The dependence of the metal-ligand resonance interaction upon the electron occupation is discussed, and a model Hamiltonian which incorporates such effects is presented. Mixed valence linear oligomers of Ru(II/III) and pyrazine are used as examples. Possible electronics applications are stressed.
TL;DR: A small amount of manganese introduced in BaTiO3 modifies strongly the vibrational and electronic properties of the pure compound as mentioned in this paper, and dielectric response and EPR measurements are reported in order to study the influence of the manganized valency on the ferroelectric-paraelectric phase transition.
Abstract: A small amount of manganese introduced in BaTiO3 modifies strongly the vibrational and electronic properties of the pure compound. Dielectric response and EPR measurements are reported in order to study the influence of the manganese valency on the ferroelectric-paraelectric phase transition.
01 Jan 1991
TL;DR: In this paper, a combination of experimental techniques is used to study the structural, optical and vibrational properties of antimony(m,v) halide salts, prototypes of class II mixed valency behaviour.
Abstract: ABSTRACf. A combination of experimental techniques is used to study the structural, optical and vibrational properties of antimony(m,v) halide salts, prototypes of class II mixed valency behaviour. The results together with simple lattice dynamics calculations lead to an estimate of an upper limit of the effective Hubbard-U for the antimony valency disproportionation. Inelastic neutron scattering is also used to study the phonon properties of the (Ba,K)(Pb,Bi,Sb)03 series. Here the CDW instability is suppressed on doping, leading to delocalisation of the electrons and the appearance of superconductivity.