Yoshinari Miura

High-Tc Phase Promoted and Stabilized in the Bi, Pb-Sr-Ca-Cu-O System

Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5~10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a=0.537 nm, b=2.682 nm, and c=3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10-6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high-Tc phase over the low-Tc phase was roughly estimated at 9/1 in volume.

Calcium apatite prepared from calcium hydroxide and orthophosphoric acid

Calcium hydroxyapatite has been prepared due to a direct precipitation reaction between 0.3m orthophosphoric acid solution and 0.1 mol calcium hydroxide dispersed in 200 ml water. The effect of the addition rate of the acid solution, reaction temperature and mixing molar Ca/P ratio is examined on the thermal stability and stoichiometry of the precipitates. Optimum conditions for HAp suitable for dense ceramics are derived from the results. The non-stoichiometry is interpreted in terms of the pH profile in the vicinity of the hydroxide particles and the state of the orthophosphate ions.

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.

Spectral properties of erbium-doped lead halotellurite glasses for 1.5 μm broadband amplification

Abstract The spectral properties of the Er 3+ -doped lead halotellurite glasses, PbX 2 –TeO 2 (X=F, Cl, Br), were measured and analyzed with Judd-Ofelt and McCumber theories. These glasses showed high refractive indices, high cross-sections for both absorption and stimulated emission, and very broad bandwidths for the 1.5 μm band. The bandwidths of the 1.5 μm band, which have substantial magnetic dipole transition component, increased significantly with the refractive index of the host materials. The halotellurite glasses have very good glass formation ability or glass stability. The halotellurite glasses will be the promising host materials for 1.5 μm broadband amplification.

Characteristics of titanium oxide films deposited by an activated reactive evaporation method

Titanium di- and sesquioxide films were epitaxially grown on the (001) surface of sapphire single-crystalline substrates by an activated reactive evaporation method. Formation range for each titanium oxide was determined as a function of oxygen pressure (Po 2 ) by means of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films prepared at Po 2 ≥ 2.0 × 10 −4 Torr were stoichiometric (100)-oriented rutile of TiO 2 , and with decreasing Po 2 they would accommodate more and more Ti 3+ ions in the rutile structure. At Po 2 = 0.6 × 10 −4 Torr, on the other hand, (001)-oriented Ti 2 O 3 was formed and an electrical transition was clearly detected at about 400 K. However, the large lattice mismatch between the substrate and these films leads to a periodic introduction of misfit dislocations in the case of the TiO 2 films and a mixing of stacking sequences for the Ti 2 O 3 films.

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.

The High-Tc Phase with a New Modulation Mode in the Bi, Pb-Sr-Ca-Cu-O System

The preparation and characterization of Bi1.73Pb0.35Sr1.89Ca1.86Cu3O9.91, a lead-rich high-Tc phase, were studied (Tc(ρ=0)=105 K). This compound crystallized in a pseudotetragonal structure with at=0.541 nm and ct=3.709 nm, while a unique one-dimensional modulation with a wavelength of 4.7 nm (≃8.7a) was found along the b axis using transmission electron microscopy. Such a lead-rich phase and a lead-free (or very poor) phase crystallizing in the well-known modulated structure (2.7 nm≃5a) were intergrown at intermediate compositions, such as Pb/Bi=1/9. Effects of annealing under different oxygen pressures were studied.

Electrochemical studies on diffusion and redox behavior of various metal ions in some molten glasses

The cathodic reactions of simple ions such as Ni2+, Co2+, Cd2+ and redox ions such as Fe3+/Fe2+, Ce4+/Fe3+, Cr6+/Cr3+ in molten sodium disilicate and a soda-lime-silica glass (16Na2O·12 CaO · 72SiO2(wt%)) were investigated by potential sweep method. Not only the reversible electrode potentials but also the diffusion coefficients of some metal ions were determined. Most of the metal ions are reduced reversibly in both the glass melts. The order of increase of reducing power was in Na2O·2SiO2 at 1350°C; Na+/Na > Mn2+/Mn > Zn2+/Zn > Co2+/Co > Cd2+/Cd > Fe3+/Fe2+ ⋍ Ni2+/Ni > As5+/ As3+ > Sb5+/Sb3+ > Ce4+/Ce3+ > Cr6+/Cr3+. This order was invariable with temperature. In 16Na2O·12CaO·72SiO2 the series was Na+/Na > Mn2+/Mn > Zn2+/Zn > Co2+/Co >Fe33+/Fe2+ > Ni2+/Ni > As5+/As3+  Sb5+/ Sb3+ > Ce4+/Ce3+ > Mn3+/Mn2+ > Cr6+/Cr3+. The relatively well linear relationships could be shown between the respective electrochemical series in both the glass melts. The equilibrium constants for Ce4+ + Fe2+ ⇌ Ce3+ + Fe3+, for example, were calculated as 9.1 and 7.2 in Na2O · 2SiO2 and 16Na2O · 12CaO · 72SiO2, respectively, at 1250°C. The diffusion coefficients of Ni2+ ions could be also represented as D = 1.96 × 10−2 exp(−32.3 × 103/RT) and D = 3.91 × 10−3 exp(−31.2 × 103/RT) in Na2O · 2SiO2 and 16Na2O · 12CaO · 72SiO2 melts. The diffusion coefficients of Co2+ ions were shown as D = 7.7 × 10−2 exp(−35.8 × 103/RT) in Na2O · 2SiO2.

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 .

Iridium oxide films via sol-gel processing

Abstract Iridium (III) ethoxide and hydrogen hexachloroiridate (IV) films were formed on glass substrates by drop-and-spread and dip-coating procedures, and heat treated to IrO 2 films. Effect of additives such as ethylene glycol, H 2 O, and HNO 3 on the microstructure of the heated films was studied as well as that of drying and heating schedules. Preciptation of metallic Ir found for several films was correlated to the high electronegativity of Ir.