Rigid covalent bond of α-Sulfur investigated via temperature-dependent EXAFS.

This study performs extended X-ray absorption fine structure (EXAFS) measurements for the S-K edge in the temperature range of 10 and 300 K in the transmission mode using a photodiode to detect the transmitted X-rays. It provides the first report of temperature variations in the structural parameters of α-S. As the temperature increases from 10 to 300 K in the Fourier transform of kχ(k), the first peak corresponding to the covalent bond of the eight-membered ring becomes slightly low anomalously despite thermal disturbances. However, as in normal materials, the second peak at 300 K decreases to approximately half of that at 10 K, which contains several intra- and inter-ring correlations. All structural parameters of the covalent bond obtained by nonlinear least squares fitting exhibit missing temperature variations. A value of zero for the asymmetric parameter in the EXAFS (C3) implies that the potential of the covalent bond is symmetric, and the constant value of the mean square relative displacement (MSRD) with temperature implies that the potential is extremely high. The Einstein model fitting for the temperature variation in the MSRD yields an Einstein temperature of 942 K and force constant (K) of 405 N/m. The value of K is the largest among those of chalcogen elements. .

Erratum: Extended X-Ray Absorption Fine Structure Study of Local Structure and Atomic Correlations of Tellurium Nanoparticles [Phys. Rev. Lett. 99, 165503 (2007)].

This corrects the article DOI: 10.1103/PhysRevLett.99.165503.

Local structure change of luminescent Ag zeolite-A and -X studied by in situ XAFS and IR spectroscopy.

The in situ X-ray absorption fine structure (XAFS) for the structural changes of Ag clusters produced in the cavity of luminescent zeolites by thermal treatment of Ag zeolite-A and Ag zeolite-X has been studied. The following procedures are compared: (i) samples are heated and cooled to room temperature under atmosphere (under air); (ii) samples are heated and cooled to room temperature in a vacuum and then exposed to air. It was confirmed that the Ag clusters were broken when the Ag zeolite was exposed to air for Ag zeolite-X, which complements our previous results for Ag12-A. It is suggested that the deformation of the Ag clusters plays an important role in the generation of a strong photoluminescence band, and Ag clusters may not be direct species producing the strong photoluminescence. The local structure of the Ag ions was found to be slightly different from that of the unheated species. The difference may originate from the formation and breakdown of Ag clusters in the zeolite cavity.

Local structure around In atoms in coherently grown m-plane InGaN film.

The local structure around In atoms in an m-plane In0.06Ga0.94N film coherently grown on a freestanding m-plane GaN substrate was investigated by polarization-dependent X-ray absorption fine-structure. A step-by-step fitting procedure was proposed for the m-plane wurtzite structure. The interatomic distance for the first nearest neighbour In-N atomic pairs was almost isotropic. For the second nearest In-Ga pairs, the interatomic distances along the m- and a-axes were longer and shorter, respectively, than that in strain-free virtual crystals as expected for the m-plane compressive strain. In contrast, the In-Ga interatomic distance in the c-direction was elongated in spite of the compressive strain, which was explained in terms of the anisotropic atomic structure on the m-plane. The local strain in the m-plane film was more relaxed than that in coherently grown c-plane single quantum wells. A few In atoms were atomically localized in all directions, and thus localized excitonic emission is expected as in the case of c-plane InGaN.

Local structure of amorphous tellurium studied by EXAFS.

The local structure of an amorphous tellurium (a-Te) film was investigated by extended X-ray absorption fine-structure analysis. The covalent bond length shortens and the Debye-Waller factor of the intra-chain decreases in a-Te compared with trigonal Te (t-Te). The value of the intra-chain coordination number is close to two, which is the value for t-Te, and the inter-chain interaction weakens. These results suggest that the primary chain structure remains intact, but the secondary structure is disrupted. The decrease in the inter-chain interaction strengthens the intra-chain interaction.

Extended x-ray absorption fine structure study of local structure and atomic correlations of tellurium nanoparticles.

Extended x-ray absorption fine structure measurements were performed on trigonal tellurium (t-Te) and tellurium nanoparticles in very thin films. Twofold coordinated chains, much like those in t-Te, exist even in the nanoparticles, but covalent bonds or intrachain interactions are stronger than those of t-Te as shown by a shorter bond length and higher Einstein temperature. The interchain coordination number of the nanoparticles is about half that of t-Te, suggesting reduction of interchain interactions.

X-ray absorption spectroscopic study on the electronic structure of Li(1)(-)(x)()CoPO(4) electrodes as 4.8 V positive electrodes for rechargeable lithium ion batteries.

Changes in the electronic structure of olivine Li(1-x)CoPO(4), 4.8 V positive electrode material for lithium ion batteries, were investigated using the X-ray absorption spectroscopy (XAS) technique. The threshold energy in the Co K-edge increased with electrochemical Li removal, indicating the oxidation of cobalt ions due to charge compensation. Moreover, P and O K-edge XAS showed a slight shift in threshold energy with Li removal. Although it is generally believed that the electrons of PO(4) polyanion do not contribute to the oxidation process, present experimental results indicate changes in the electronic structure around PO(4) units. Such results would be interpreted by the idea of the hybridization effect between the Co 3d and O 2p orbitals and of the polarization effect introduced by Li ions.