Tokuro Nanba

Coordination change of Te atoms in binary tellurite glasses

Coordination changes of Te(+ IV) atoms were derived from Raman and X-ray photoelectron spectra of the binary tellurite glasses containing Li, Na, Ba and Zn. A structure model consistent with the experimental results was proposed. In this model, TeO4 units were converted mainly to O22Te=O and O12Te(=O) O− in the range of lower atomic ratio O/Te, and the rate of increase of TeO3/TeO4 decreased in the range of higher O/Te because of the equilibrium TeO42 ↔ O22TeO. The increase in the fraction of non-bridging oxygen atoms and three-coordinated Te(+ IV) atoms was confirmed by X-ray photoelectron spectra. The fraction of non-bridging oxygen estimated from X-ray photoelectron spectra agreed well with that from the Raman spectra and the model.

X-ray photoelectron spectroscopy of alkali tellurite glasses

Abstract X-ray photoelectron spectra of R2OTeO2 (R: Li, Na, K, Rb and Cs) glasses were measured, using a fresh surface fractured in an ultra high vacuum (≈ 7 × 10−8 Pa) and irradiated with a monochromatic Al K α X-ray (hv = 1486.6 eV). The O ls photoelectron spectra showed only a single Gaussian-Lorentzian peak and the peak shifted toward smaller binding energy with increase in Lewis basicity of oxide ions in the glasses. Two peaks attributed to BO and NBO were not observed. In the near valence band spectra for the lithium tellurite glasses, the spectral profile gradually became similar to that of a Li2TeO3 crystal with increase in Li2O content up to 30 mol% Li2O. This variation of the profile is correlated to the change in the coordination structure of the tellurium atoms (TeO4 trigonal bipyramids → TeO3 trigonal pyramids) with the addition of the alkali oxides.

X-ray photoelectron spectroscopy of sodium borosilicate glasses

Abstract X-ray photoelectron spectra of RNa2O·B2O3·KSiO2 (R=0.2 to 5.0,K=0.5 to 6.0) glasses were measured by a monochromatised Al-Kα XPS instrument. Chemical shifts of the core-level photoelectron spectra of the glass constituent ions were investigated. Peaks at the higher and lower energy sides of an O1s signal were ascribed to bridging oxide (BO) and non-bridging oxide (NBO) components, respectively. The BO component could not be separated into the oxide ions with different environment such as Si–O–Si, B–O–Si and B–O–B. Na1s signal could not be separated into two components of Na+ ions associated with [BO4/2]− tetrahedron and NBO. For the small K values (=0.5 and 1.0), the NBO fractions measured by XPS agreed very well with the structural model proposed by Dell et al. [J. Non-Cryst. Soilds 58 (1983) 1], where NBO did not appear until R=0.5 regardless of K values. With increasing K, however, the dependence of the NBO fraction upon R gradually came to disagree with the Dell model. At smaller R values than R0=0.5+K/16, the NBO component already appeared to a considerable extent and the discrepancy between the XPS results and the Dell model became more significant with increasing K. This fact meant that additional sodium oxides were shared proportionally between silicate and borate networks even at the small R when K was larger than 2. A new sharing model was proposed on the basis of an acid–base concept.

Structural study of amorphous WO3 thin films prepared by the ion exchange method

The structure of amorphous tungsten trioxide films was investigated with IR and Raman spectroscopic analyses and an XRD method. The films were prepared by ion exchange from sodium tungstate as a starting material. Films consisted of microclusters of 10–30 A diameter, in which the networks are formed with WO 6 octahedra sharing their corners and edges. The networks in the as-prepared samples consisted of WO 6 units with low symmetry, in which termination by W=O and W—OH 2 groups was common. As the post-annealed temperature became higher, the symmetry of WO 6 was improved and the edge-sharing octahedra disappeared.

Oriented surface crystallization of lithium niobate on glass and second harmonic generation

Surface crystallization of LiNbO 3 on xK 2 O.(35-x)LI 2 O.30Nb 2 O 5 .35SiO 2 (0 ≤ x ≤ 35) (mol%) glasses was investigated. The c-axis orientation of surface crystallized LiNbO 3 was improved when the glass contained 10 mol% K 2 O. Furthermore, Li ions in the LiNbO 3 crystallites were partially replaced by K ions from the glass. Transparent surface crystallized LiNbO 3 films on glasses were prepared by controlled heat treatment, which showed optical second harmonic generation. The estimated second-order non-linear optical susceptibilities were d 33 = 6.40 pm/V and d 31 = d 21 = d 24 = d 15 = 1/3d 33 = 2.14 pm/V for a film 1.33 μm in thickness prepared after heating at 620°C for 3 h, when the c-axis oriented film was described by a space group C xv .

Characterization of amorphous tungsten trioxide thin films prepared by rf magnetron sputtering method

Abstract Amorphous tungsten trioxide thin films were prepared using a rf magnetron sputtering method. The relation between structure and electrochromic properties was investigated. At the macroscopic level, the films had dense structures. From Raman spectroscopic and X-ray radial distribution analyses, it was deduced that the networks were basically formed by three-, four- and six-membered rings of corner-sharing WO6 octahedra, and in the films with low O/W atomic ratios many edge-sharing units were present. It was also found that the films with high O/W ratios showed good electrochromic properties, which were closely related to the six-membered rings.

EXAFS of tellurium in the glasses of the B2O3TeO2 system

TeK-edge spectra were measured for binary glasses of compositions 0.16B 2 O 3 · 0.84TeO 2 and 0.301B 2 O 3 · 0.699TeO 2 . Te O bond length and coordination number of Te atoms were analyzed to be very similar to those of paratellurite. Within errors of measurement, all the Te atoms were four-coordinated and TeO + 3 units were absent in the glasses. It was concluded that some other mechanism should be present to compensate for a negative charge on four-coordinated boron atoms in the glasses.

Infrared and Raman spectra of binary tellurite glasses containing boron and indium oxides

The constitution of glasses in the systems M2O3-TeO2 (M = B and In) was investigated by Raman and infrared spectroscopy. From the relation between the M2O3 content and the intensity ratios of the deconvoluted Raman peaks I(720)/I(665) and I(780)/I(665), it was concluded that In2O3 behaves as a network modifier to yield TeO3−units and that discrete BO3 and BO4 units construct a network of glasses containing boron oxide. A structural model for those glasses was derived which involves three-coordinated oxygen atoms and TeO4 units of an intermediate configuration, O3Teδ+ ...Oδ-.

Segregation and dissolution reactions of the 2223 phase in the Bi, Pb-Sr-Ca-Cu-O system on annealing in air

Abstract Thermal behavior of the Pb-substituted Bi-2223 phase was examined by characterizing samples annealed at 500°C to 850°C in air and also those subsequently reheated at 850°C in air by XRD, SEM and magnetic measurements. Very interesting reactions occurred, which were segregation of precipitates on annealing below 830°C and dissolution of the precipitates on subsequent reheating at 850°C into the 2223 phase. The precipitates were identified as Sr 2.5 Bi 0.5 Pb 3 Ca 2 CuO 2 . The precipitation and the dissolution were clearly confirmed by morphological observations of a fixed portion of a sample before and after heat treatments. These results strongly suggest that the 2223 phase changes its composition reversibly between the relatively Pb-rich composition stabilized above 850°C and relatively Pb-poor ones stabilized in essentially the same structure below 830°C. However, T c remained almost constant at 113 K.

X-ray and neutron scattering study of the structure of lithium bismuth oxide glass

Abstract The structure of (100−x)Bi2O3·xLi2O ( 25⩽x⩽35 mol % ) glasses has been investigated by means of X-ray and neutron scattering methods. Comparing the glasses with several bismuthate crystals in total correlation function T(r), it is concluded that a large amount of edge-sharing BiOn polyhedra are present in the glasses and the network structure is similar to the Bi2O4 crystal. In the crystal, BiO6 octahedra form a layer sharing their four corners mutually, and the BiO4+4 distorted polyhedra are placed between the layers sharing all the edges with the neighboring polyhedra. Assuming two different Li sites in the Bi2O4-based structure, structural models were constructed to compare T(r), from which it was suggested that some Li ions substituted for the octahedral Bi site and some occupied an interstitial vacant site. In addition, the glasses have various defects such as excess O ions, positive-holes on O ions, vacant space to accept atmospheric oxygens, and Bi vacancies. The glass formation is sensitive to the melting conditions, such as temperature and period, suggesting that there exists some optimum quantity in the defect structures.