Electron spin resonance (ESR) and 14C dating in sediments of Bonaire, Leeward Antilles

The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire's eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extreme-wave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine-grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy.

Electron spin resonance studies of d5 ions (Fe3+ and Mn2+) in lead oxide-lead halide glasses

Electron spin resonance (ESR) of d5 ions (Fe3+ and Mn2+) has been investigated in PbO---PbF2 and PbO---PbCl2 glasses in wide ranges of composition. ESR spectra of d5 ions in these glasses exhibit significant differences which we have attributed to at least three important causes: (i) The ionic potentials of Fe3+ and Mn2+ are different. Hence Fe3+ ions tend to acquire their own environment while Mn2+ ions take up substitutional (Pb2+ ion) positions. (ii) The sizes and nephelauxetic behaviours of O2- and F- ions are similar. Thus even when there is a mixed anionic coordination, the environment of Mn2+ ions is highly symmetrical in oxyfluoride glasses. The Mn2+ spectra in oxychloride glasses are considerably different. (iii) Increase in halide ion concentration increases the ionicity of lead-ligand bonding and favours a more symmetrical environment around dopant ions in halide-rich glasses. The features in ESR spectra have been interpreted in the light of known behaviour of d5 ions in glasses and also in the context of known structural features of PbO---PbX2 glasses. Dopant ions appear to cluster at high concentrations although isolated low-symmetry sites are still observed. Effects of crystallization and annealing upon ESR spectra have also been investigated.

Long lasting phosphorescence, thermoluminescence and electron spin resonance property of Mn2+ activated ZnO-Al2O3SiO2 ceramic

The long lasting phosphorescence (LLP) phenomenon in Mn2+-doped ceramic based on ZnO-Al2O3-SiO2 (ZASM) is observed. After irradiation by a UVP standard mercury lamp peaking at 254 nm with a power of 0.6 mW/cm(2) for 15 min, the ceramic sample emits a bright green light peaking at 519 nm, which can be seen in the dark even 15 h after the removal of UVP standard mercury lamp by the naked eyes whose limit of light perception is 0.32 mcd/m(2). The initial afterglow intensity reaches about 1900 mcd/m(2), and the color coordinate (X, Y) is (0.2280, 0.5767) at about 10 s after stopping irradiation. The thermoluminescence (TL) spectra show that there are at least three kinds of trap centers with different trap levels while electron spin resonance (ESR) spectra indicate that there are electron- and hole-trapping centers induced after irradiation by a UVP standard mercury lamp. Based on these measurements, the LLP is considered to be due to the recombination of electrons and holes at trapping centers with different levels, which are firstly thermally released back to Mn2+ and then give rise to the bright green LLP at room temperature.

Electron spin resonance of Gd3+ in the antiferromagnetic heavy fermion CeIn3 and its reference compound LaIn3

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Two-phase separation observed in thermally treated pellets of ClO4- doped poly(3-methylthiophene) from electron spin resonance measurements

A pressed pellet of CIO (-)(4) poly (3-methylthiophene) (P3MT) was heated for two hours at 85 degrees C and suddenly dropped in liquid nitrogen. A change was observed around 220 K in the Electron Spin Resonance (ESR) spectra when the sample was slowly cooled from room temperature. ESR line asymmetry parameter (A/B) showed two spatially separated phases. One was identified as a small metallic-like phase. The other phase, the larger one, makes a transition to a semiconducting Charge-Density Wave (CDW) state.

Role of oxygen vacancies in the magnetic and dielectric properties of the high-dielectric-constant system CaCu3Ti4O12: An electron-spin resonance study

We report experiments of electron spin resonance (ESR) of Cu2+ in polycrystalline samples of CaCu3Ti4O12 post-annealed in different atmospheres. After being synthesized by solid state reaction, pellets of CaCu3Ti4O12 were annealed for 24 h at 1000 degrees C under air, Ar or O-2. Our temperature dependent ESR data revealed for all samples nearly temperature independent g value (2.15(1)) and linewidth for T > T-N approximate to 25 K. However, the values of ESR linewidth are strongly affected by the oxygen content in the sample. For instance, argon post-annealed samples show a much larger linewidth than the O-2 or air post-annealed samples. We attribute this broadening to an increase of the dipolar homogeneous broadening of the Cu2+ ESR lines due to the presence of oxygen vacancies which induce an S=1/2 spin inside the TiO6 octahedra. Correlation between a systematic dependence of the ESR linewidth on the oxygen content and the high dielectric constant of these materials is addressed. Also, ESR, magnetic susceptibility, and specific heat data for a single crystal of CaCu3Ti4O12 and for polycrystals of CdCu3Ti4O12 are reported.

Evidence of weak ferromagnetism in doped plasticized polyaniline (PANI-DDoESSA)0.5 from electron spin resonance measurements

X-band electron spin resonance (ESR) measurements have been performed on a conducting free-standing film of polyaniline plasticized and protonated with di-n-dodecyl ester of sulfosuccinic acid (DDoESSA). The magnetic field was applied parallel and perpendicular to the plane of the film. At around 75 K a transition is observed from Pauli susceptibility to a localized state in which the spin 1/2 polarons behave as spin 1/2 dimers. A rough estimation of the intradimer and interdimer exchange constants is obtained. Below 5 K, ESR data reveal a weak ferromagnetism with the Dzyaloshinskii-Moriya vector mainly oriented in the plane of the film. The existence of a relatively well-defined n-fold axis along the chain direction in the crystalline regions confers a symmetry compatible with such analysis. © 2013 IOP Publishing Ltd.

Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electron- Spin-Resonance studies of phase transitions in double propionates

Detailed ESR investigations of Mn2+ substituting for Ca2+ in Ca2Sr(C2H5COO)6, (DSP) and Ca2Pb(C2H5COO)6, (DLP) and Ca2Ba(C2H5COO)6, (DBP), in single crystals and powders, over the temperature range from 300°C to -180°C have been carried out to study the successive phase transitions in these compounds. Spectra have been analyzed in terms of axial spin Hamiltonians and the temperature dependences of the parameters studied. Across the I-II transition, new physically and chemically inequivalent sites appear indicating the disappearance of the diad axes on which the propionate groups are located, bringing out the connection between the motional states of the propionate groups and the occurrence of ferroelectricity. The II-III transition also causes chemically inequivalent sites to develop, indicating that the transitions may not be isomorphous as believed previously. Similarities and dissimilarities of the ESR spectra of DLP, DSP and DBP are discussed in relation to the phase transitions.

Dielectric and Electron Spin Resonance Spectroscopic Studies of Glassy Crystalline States of Organic Compounds

Dielectric studies of the glassy crystalline states of cyclohexanol, cyclohexanone, and camphor obtained by upercooling the plastic crystalline phase demonstrate the presence of characteristic a- and p-relaxations. The parameters of the a-relaxation fit the Vogel-Tammann-Fulcher (VTF) equation. ESR spin-probe studies of the glassy crystalline phase of cyclohexanol show that there is a marked decrease in the correlation time above the glasslike transition temperature. The present studies suggest the similarity between glassy crystals having long-range orientational disorder and glasses which are known to betra nslationally disordered.

An electron-spin-resonance study of MN2+ doped calcium hydrazine carboxylate monohydrate

Single crystals of calcium hydrazine carboxylate, monohydrate have been studied by ESR of Mn2+ doped in the calcium sites. X-band ESR indicated a large crystal field splitting necessitating experiments at Q band. The analysis shows two magnetically inequivalent (but chemically equivalent) sites with g(xx) = 2.0042+/-0.0038, g(yy) = 2.0076 +/-00029, g(zz) =2.0314+/-0.001, A(zz) = 0.0099+/-0.0002 cm(-1), A(xx) = 0.0099+/-0.0002 cm(-1), A(yy) = 0.0082+/-0.0002cm(-1), D = 3/2D(zz) = 0.0558+/-0.0006cm(-1), and E = 1/2(D-xx-D-yy) = 0.0127+/-0.0002 cm(-1).One of the principal components of the crystal field, (D-zz), is found to be along the Ca<->Ca direction in the structure and a second one, (D-xx), along the perpendicular to the plane of the triangle formed by three neighbouring calciums. The A tensor is found to have an orientation different from that of the g and D tensors reflecting the low symmetry of the Ca2+ sites.