Showing papers on "Valency published in 2008"

New Magnetic Transitions in the Ordered Oxygen-Deficient Perovskite LnBaCo2O5.50+δ

Abstract: The investigation of the ordered oxygen-deficient perovskites LnBaCo 2 O 5.50+δ with Ln = Eu and Sm shows that a small deviation from the "O 5.50 " stoichiometry influences dramatically the magnetic properties of this structural type. Three ferromagnetic (FM) states can be obtained, depending on the oxygen content, 6. For a cobalt valency close to +3 (δ ∼ 0) a ferromagnetic ordering FM1 takes place around 250 K, previously observed for Ln = Gd, Tb cobaltites. For 6 +0.10) a new ferromagnetic state FM3 appears, involving Co 3+ -O-Co 4+ superexchange interactions.

Mixed valency and magnetism in cyanometallates and Prussian blue analogues

Abstract: Prussian blue (PB) is a well-known archetype of mixed valency systems. In magnetic PB analogues {CxAy[B(CN)6]z}.nH2O (C alkali cation, A and B transition metal ions) and other metallic cyanometalla...

Mixed valency in organic charge transfer complexes

Abstract: Mixed-valence (partial charge transfer state) and segregated stacking are the key factors for constructing organic metals. Here, we discuss the ionicity phase diagrams for a variety of charge transfer systems to provide a strategy for the development of functional organic materials (Mott insulator, semiconductor, superconductor, metal, complex isomer, neutral-ionic system, etc.).

Element- and site-specific oxidation state and cation distribution in manganese ferrite films by diffraction anomalous fine structure

Abstract: Epitaxial manganese ferrite thin films were studied by x-ray diffraction anomalous fine structure to obtain element-specific and site-specific information on site occupancy, local structure, and valency. These properties were introduced to molecular field theory to reproduce thermomagnetization curves and determine superexchange energy, Neel temperature, and spin canting angle.

Charge density coordination and dynamics in a rodlike polyelectrolyte.

Abstract: We study static and dynamic correlation functions of segmental charge density fluctuation on a rodlike polymer in ionic solutions. The polymer is described by an effective Hamiltonian which incorporates the Coulomb interaction between fluctuating charges screened by ionic fluid environment. We analytically calculate the correlation functions and discuss how charge distribution and dynamics are affected by counterion valency and concentration in electrolyte. We find that the charge correlation exhibits an underdamped oscillation with a wavelength comparable to the counterion size and with the amplitude increasing with the counterion valency. The dynamic correlation of charge density is shown to decay with a characteristic time varying with the counterion valency and concentration. The multivalency gives rise to faster decay of the correlation than that given by one dimensional diffusion.

Mixed valence complexes involving MM quadruple bonds (M=Mo or W).

Abstract: The MM quadruple bond of configuration MM 242 is redox active and in many ways ideally suited for studies of mixed valency when two or more such centres are linked by a bridging ligand. In this acc...

Effective interactions in the periodic Anderson model in the regime of mixed valency with strong correlations

Abstract: For the periodic Anderson model in the strong correlation regime, we construct the effective Hamiltonian Heff up to terms of the fourth order in the parameter V/U, where V is the hybridization interaction intensity and U is the intra-atom Coulomb repulsion strength. This Hamiltonian contains interactions inducing both magnetic ordering and Cooper instability under conditions of a mixed valency of rare-earth ions. Based on numerical calculations, we obtain information about the dependences of the effective interaction parameters on the distance between crystal lattice sites. We demonstrate that realizing exchange interactions corresponds to a strongly frustrated system of localized spin moments and facilitates the suppression of the antiferromagnetic order parameter with a possible transition to the state of a quantum spin liquid. It is essential that among the terms in Heff inducing the transition to the superconductivity phase, there are terms resulting in the d-type symmetry of the superconductivity order parameter; such a symmetry is realized in many heavy-fermion compounds.

The chemical response of main-group extended solids to formal mixed valency: the case of LixBC

Abstract: The introduction of mixed valency into extended main-group solids is discussed using the example of hole-doped LiBC, where a combination of experimental measurements and density functional theory calculations is used to understand the observed electronic properties in terms of deviation from the expected rigid-band electronic structure behaviour.

Mixed valency in rare-earth fullerides.

Abstract: Mixed-valence phenomena associated with the highly correlated narrow-band behaviour of the 4f electrons in rare earths are well documented for a variety of rare-earth chalcogenides, borides and intermetallics (Kondo insulators and heavy fermions). The family of rare-earth fullerides with stoichiometry RE2.75C60 (REZSm, Yb, Eu) also displays an analogous phenomenology and a remarkable sensitivity of the rare-earth valency to external stimuli (temperature and pressure) making them the first known molecular-based members of this fascinating class of materials. Using powerful crystallographic and spectroscopic techniques which provide direct indications of what is happening in these materials at the microscopic level, we find a rich variety of temperature- and pressure-driven abrupt or continuous valence transitions—the electronically active fulleride sublattice acts as an electron reservoir that can accept electrons from or donate electrons to the rare-earth 4f/5d bands, thereby sensitively modulating the valence of the rare-earth sublattice.

Can Complex Valency Frames be Universal

Abstract: This paper deals with the comprehensive lexicon of Czech verbs named VerbaLex. It contains complex valency verb frames (CVFs) including both surface and deep valencies. The most notable features of CVFs include two-level semantic labels with linkage to the Princeton and EuroWordNet Top Ontology hierarchy and the corresponding surface verb frame patterns capturing the morphological cases that are typical of the highly inflected languages like Czech. We take the position that CVFs can be suitable for a description of the argument predicate structure not only of Czech verbs but also verbs in other languages, particularly Bulgarian, Romanian and English.

Aluminum and gold deposition on cleaved single crystals of Bi2CaSr2Cu2O8 superconductor

Abstract: We have used photoelectron spectroscopy to study the changes in the electronic structure of cleaved, single crystal Bi2CaSr2Cu2O8 caused by deposition of aluminum and gold. Al reacts strongly with the superconductor surface. Even the lowest coverages of Al reduces the valency of Cu in the superconductor, draws oxygen out of the bulk, and strongly modifies the electronic states in the valence band. The Au shows little reaction with the superconductor surface. Underneath Au, the Cu valency is unchanged and the core peaks show no chemically shifted components. Au appears to passivate the surface of the superconductor and thus may aid in the processing of the Bi‐Ca‐Sr‐Cu‐O material. These results are consistent with earlier studies of Al and Au interfaces with other, polycrystalline oxide superconductors. Comparing with our own previous results, we conclude that Au is superior to Ag in passivating the Bi‐Ca‐Sr‐Cu‐O surface.

An OT Analysis on Verb Reduplication in Hakka

Abstract: This paper investigates the obligatory syntactic process in Hakka called ”verb reduplication”, of which a verb is reduplicated when followed by a CP headed by the clitic do. By providing an OT-based analysis, this paper argues that the syntactic operation is triggered by two ABUT constraints. When a verb takes a do-phrase to further describe its denoted action, if there exists another constituent in-between the verb and its following CP, attaching do to either the verb or the intervening constituent violates one of the ABUT. Hence, the verb must be reduplicated to create a structure that fulfills the requirement of both constraints. Contrastively, if the do-phrase immediately follows the verb, attaching do to its preceding main verb does not violate any of the ABUT. Here, the disallowance of verb reduplication can be captured by the Obligatory Contour Principle (OCP), which functions as a crucial syntactic condition to block reduplication, knowing that its occurrence would cause the adjacency of two identical verbs.

An Applicative-Construction Analysis of Two Types of Chinese Non-Core Arguments

Abstract: Two types of Chinese non-core arguments can undergo applicativization: one related to mono-transitive verbs and the other to intransitive verbsThese two types of non-core arguments are linked to the event denoted by the VP via the semantic light verb APPLINVOLVE and result in High applicative constructionsIn English,only the non-core arguments that are added to mono-transitive verbs can undergo applicativizationThese non-core arguments are linked to the THEME arguments of the verbs and result in Low applicative constructionsSeen from the perspective of applicative constructions,the so-called double-object construction is actually the combination of the VP projected by a mono-transitive verb and an APPLP projected by an APPL head;the so-called ditransitive verb can be taken as a mono-transitive verb that comes into relation with a non-core argument licensed by an APPL head in syntactic derivation

Comment on “Characterization of As-doped, p-type ZnO by x-ray absorption near-edge structure spectroscopy: Theory”

Abstract: In a recent letter, S. Limpijumnong et al. have simulated the partial density of states for As atoms and compared their simulated results with the x-ray absorption near-edge structure XANES spectrum at As K edge of the ZnO:As film and concluded that our experimental results support their model. The conclusion drawn in Ref. 1 contradicts the use of XANES as a chemical speciation and valency identification technique and hence our experimental interpretation shown in Ref. 2. This spectroscopy is based on the fact that the binding energy of an element varies with its valency and has been routinely used in semiconductors to identify the valency of dopants or reactants. The XANES at As K edge of the As-doped, n-type ZnO Fig. 1 in Ref. 2 reveals As in the oxidation state of 5+ As5+ , signifying the formation of As–O bonding As occupying Zn site and also the presence of 3− oxidation state of As As3− , thereby confirming As–Zn bonding As occupying O site in the as-grown film. However, after rapid thermal annealing RTA , As is only in 3− state indicating that As occupies O sites. This apparently suggests that there is a change in the chemical environment implying that both these films possess different electronic structures. In the as-grown state we have arsenic oxide which is absent after RTA. Therefore, we argued the presence of As3− could be responsible for p-type behavior and compensation of electrons takes place only after RTA. Both the oxidation states of As identified from As K edge and spectral changes at O K edge support such argument. Above approach was followed previously by Fons et al. who used XANES at Cu and N K edges to investigate respectively the valency of Cu in Cu doped epitaxial ZnO films and N doping in ZnO. In a similar way, Cheong et al. used XANES at As K edge to identify the valency of the residual site of As in oxidized AlxGa1−xAs and Rodriguez et al. used XANES at N and O K edges to understand the reaction of NO2 with Zn and ZnO. Limpijumnong et al. projected that our results are in good agreement to support their model just based on the simulation of one particular spectrum and ignored many open questions concerning charge state and all possible defect models. A careful observation of Figs. 2 b –2 d in Ref. 1 shows that As on oxygen defect has unfilled states closer to the valency band maximum than the defect complex AsZn-2VZn and also the As on O defect is relatively shallower. Apart from this, it is not clear why a neutral AsZn-2VZn defect should be responsible for As K edge XANES spectrum of p-type ZnO and also if the defect cluster is neutral, it would result in deep level defect which may not be responsible for making p-type ZnO. In our opinion, there are still many unknowns in their models to resolve, such as the question whether electrically active As acceptors are due to AsO or AsZn-2VZn complex. In other words, it is difficult to account for the type of defects in n-type and p-type ZnO and also to suggest a universal model for these two different chemical compounds and the changes that occur in going from n-type to p-type behavior due to RTA. We believe that confirmation by an experimental tool is more advantageous to understand the underlying physics and the local electronic structure around the acceptor in ZnO.

Bardi Complex Predicates as a Challenge to Monotonicity

Abstract: Bardi (Nyulnyulan, Australian) has both simple and complex predicates and extensive morphological marking on the inflecting verb for agreement and valency. While in simple predicates valency marking is straightforward, in complex predicates there is a mismatch, a ‘missing’ argument which is marked in the verb but is not subcategorised for in the argument structure. It appears that the coverb modifies the f-structure introduced by the light verb – if so, this is a clear violation of monotonicity.

First Steps in Building a Verb Valency Lexicon for Romanian

Abstract: This paper presents some steps in manually building a verb valency lexicon for Romanian. We refer to some major previous works by focusing on their information representation. We select that information for different stages of our project and we show the conceptual problems encountered during the first phase. Finally we present the gradually building procedure of the lexicon and we exemplify the manner in which the information is represented in a lexicon entry.

Mn 3s-2p x-ray emission spectra for La 1-x Sr x MnO 3

Abstract: Introduction Perovskite-type Mn oxides attract a great deal of interest from both fundamental and applicational viewpoints because of their interesting properties such as the CMR effect. The Mn 3d electrons in the compounds are closely related to those properties. The number of the 3d electrons in a given Mn compound can be evaluated by measuring the Mn 3s photoemission spectroscopy (PES) spectrum. The spectrum exhibits a double-peak structure, the so-called exchange splitting resulting from the exchange interaction between the Mn 3s hole and the Mn 3d electrons. The splitting energy depends on the number of the 3d electron or Mn valency. Galakhov et al. have illustrated the fair correlation between the splitting energy and the Mn valency of Mn oxide [1]. We also found the Mn 3s PES spectrum for Pr0.5Ca0.5MnO3 reflecting change in the Mn valency across the charge-order transition [2]. The PES spectrum is, however, more or less surfacesensitive and sometimes gives misleading information on the inherent bulk nature of the material. In addition the spectrum for the insulating material suffers the charging effect by photoirradiation. On the other hand x-ray emission spectroscopy (XES) is much less surfacesensitive and is not affected by the charging effect. The 3s-2p radiative transition leaves the 3s hole. Thus the Lη and Ll, i.e. 3s-2p1/2 and 3s-2p3/2, respectively, XES spectra for Mn compounds also exhibit the exchange splitting. It has been found that the Lη spectrum for Mn oxides does exhibit the double-peak structure reminiscent of the Mn 3s PES spectrum, whereas it is hard to evaluate undoubtedly the splitting energy in the Ll spectrum [3]. We have measured the Lη spectrum for a series of La1xSrxMnO3 from x=0 to 1 and investigate the correlation between the exchange-splitting energy and the Mn valency of La1-xSrxMnO3.

Construcciones con verbo duplicado

Abstract: In Spanish, duplicated verb constructions are very common. In terms of its morphosyntactic codification, the duplicated verb appears in four different forms: with an auxiliary verb, without an auxiliary verb, with a plain inflected verb, and with an adverbial function. In terms of its semantics, this verbal form expresses two basic senses: iteration and emphasis. In the former, the duplicated verb denotes that a specific state of affairs, in certain linguistic contexts, is realized more than once in an undetermined way (except for states). In the latter, and within other linguistic circumstances, the duplicated verb carries only an emphatic value.

The Role of Limited Valency and Bonding Orientation on Phase Behavior

Abstract: Nanoparticles functionalized by single strands of DNA have been shown to be highly customizable building blocks for self-assembled nano-structures, giving rise to complex networks that have very unusual phase diagrams. Specifically, the nanoparticles exhibit a phase diagram which contains three critical points; the presence of two critical points is rare in nature, but has been found in some natural substances like water. In this thesis, we use lattice models to examine which nearest neighbor interactions are important to generate multiple distinct phases. We show that the multiple critical points cannot be reproduced via limiting the number of bonding neighbors alone. Development of more complex lattice models that may include such behavior based on our results is ongoing.