Synthesis of new compounds of the pseudo-ternary system SrO-Bi2O3-TeO2 in air

The phase equilibria of the pseudo-ternary system SrO-Bi₂O₃-TeO₂ at 600 to 850 C were examined in air by solid-state reaction techniques and X-ray powder diffraction. Three pseudo-ternary compounds were found: a hexagonal solid solution Bi₂O₃ · 2xSrO · 5xTeO₂ (x = 0.02 to 0.20,a = 0.394(1) to 0.399(5),c = 1.89(6) to 1.86(7) nm), a rhombohedral phase Bi₄Sr₃Te₅O₁₉ (a = 0.405(2),c = 2.71 (5) nm in hexagonal terms) and a cubic phase Bi₂SrTeO₇ (a = 1.086(9) nm). The Mössbauer spectra of¹²⁵Te in the compounds indicated that the tellurium atoms were mostly in the state of Te⁺⁴ in the former two compounds but were exclusively Te⁺⁶ in Bi₂SrTeO₇. The electrical conductivity of the first two were about 10^–2–1 cm^–1 at 600 C. However, Bi₂SrTeO₇ was an electrical insulator.     

Dielectric dispersion in ZnF2-Bi2O3-TeO2 glass system

Dielectric constant , loss tan and ac conductivity of ZnF₂-Bi₂O₃-TeO₂ glasses with varying concentrations of Bi₂O₃ (from 5 to 20%) are studied as a function of frequency and temperature over moderately wide ranges. The dielectric breakdown strength for these glasses is also determined in air medium. From the analysis of these studies along with the IR spectra & DTA recordings of these glasses, the structural changes in ZnF₂-Bi₂O₃-TeO₂ glass system with change in the concentration of Bi₂O₃, are discussed.     

Optical absorption studies for TeO2-P2O5 and Bi2O3-TeO2-P2O5 glasses

A range of TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ glass systems were prepared. The optical absorption spectra were measured in the spectral range 300–800 nm and it was found that the fundamental absorption of these glasses is dependent on the glass composition. The optical energy gap of binary glasses increases with increasing TeO₂ content while the addition of Bi₂O₃ to TeO₂-P₂O₅ decreases the optical energy gap. The absorption edges of these glasses arise from direct forbidden transitions and occur at photon energies in the range of 2.17 to 2.97 eV for TeO₂-P₂O₅ glasses and 2.63 to 2.32 eV for Bi₂O₃-TeO₂-P₂O₅ glasses depending on their composition.     

Seebeck coefficient of V2O5-R2O3-TeO2 (R = Sb or Bi) glasses

The thermoelectric power of glasses in the systems V₂O₅-Sb₂O₃-TeO₂ and V₂O₅-Bi₂O₃-TeO₂ was measured at temperatures in the range 373–473 K. The glasses in both systems were found to be n-type semiconductors. The Seebeck coefficient, Q, at 473 K was determined as –192 to –151 VK^–1 for V₂O₅-Sb₂O₃-TeO₂ glasses, and –391 to –202 VK^–1 for V₂O₅-Bi₂O₃-TeO₂ glasses. For these glasses in both systems, Heikes' formula was satisfied adequately for the relationship between Q and In [C _v/(1-C_v)] (C _v = V⁴⁺/V_total, C _v is the ratio of the concentration of reduced vanadium ions), and discussions confirmed small polaron hopping conduction of the glasses in both systems. Mackenzie's formula relating to Q and V⁵⁺/V⁴⁺ was also applicable to the glasses in both systems, and it was concluded that the dominant factor determining Q was C _v.     

Glass formation range in the SeO2-TeO2-V2O5-MoO3 system

The glass forming region in the quaternary system under increased oxygen pressure and at a slow melt cooling rate (2 to 2.5° C min^-1) has been determined. The stable glasses are located in the central part of the system but nearer to the SeO₂-TeO₂ side. The structural units of these two glass formers are of decisive importance in building up the glass lattice. Infrared spectra of selected compositions from the glass forming region are taken. From the data obtained for the binary glasses in the TeO₂-V₂O₅, TeO₂-SeO₂, TeO₂-MoO₃, V₂O₅-MoO₃ systems and the spectra of the four component compositions, it is shown that the basic structural units participating in the glass lattice formation are the SeO₃, VO₅, TeO₄ and TeO₃ groups. Structural models are proposed: glasses in the SeO₂ direction possess laminar and chain structure, while with increase of TeO₂ concentration, a three-dimensional structure is built up.     

Phase equilibrium relations in the binary system Bi2O3-ZnO

Phase equilibria in the binary system Bi₂O₃-ZnO were studied by quenching technique. Heat-treated compositions were subjected to X-ray diffraction for phase identification, and differential thermal analysis, optical and scanning electron microscopy were used to determine the solid-liquid equilibria occurring in this system. The data thus obtained revealed that incorporation of a small amount of ZnO to the high-temperature face-centered cubic lattice of Bi₂O₃ leads to the formation of a body-centered cubic solid solution (-Bi₂O₃), which extends up to a composition of 2.2 mol% ZnO at a temperature near 750°C. On cooling, the -Bi₂O₃ solid solution undergoes a eutectoid transformation at a temperature of 710°C to yield the low-temperature monoclinic polymorph of Bi₂O₃ (-Bi₂O₃) and Bi₃₈ZnO₅₈. The eutectoid occurs at a composition of 1.8 mol% ZnO. The compound Bi₃₈ZnO₅₈ has a crystal structure analogous to the body-centered cubic -Bi₂O₃ solid solution and melts incongruently at a temperature near 753 ± 2°C to yield -Bi₂O₃ and liquid. A binary eutectic occurs between Bi₃₈ZnO₅₈ and ZnO at a composition near 25 ± 1.0 mol% ZnO with a melting temperature of 738 ±2°C. Based on the data obtained in this study, a revised phase diagram of the binary system Bi₂O₃-ZnO is proposed.     

Some details of the ternary system Bi2O3-CaO-CuO

Before investigating the ternary system Bi₂O₃-CaO-CuO, a revision of the binary bounding system Bi₂O₃-CaO was first necessary. In the range between 20 and 70 mol % CaO the solid solutions and '₁ and the stoichiometric compounds Bi₂CaO₄, Bi₆Ca₄O₁₃, and Bi₂Ca₂O₅ were found to exist for 675 °CT780 °C. Above 780 °C a new high temperature compound with the formula Bi₆Ca₅O₁₄ has been identified. The X-ray powder diffraction data, unit cell dimensions, as well as the space group, have been reported. The ternary system contains no intermediate compounds and also no solubility was found for the binary bounding phases. Below 780 °C all the Bi-Ca oxides mentioned above are in equilibrium with CuO. At 820 °C, a wide liquidus field is dominating so that these quasibinary equilibria disappear. For 780 °C6Ca₅O₁₄ forms an equilibrium with Ca₂CuO₃ and CuO. Other equilibria are deduced. For a fixed ternary composition the reaction path of the sintering process was investigated as a function of time and temperature.     

TiO2–Bi2O3 Materials

The electrical conductivity, magnetic susceptibility, and catalytic activity (photoreduction of Methylene Blue to a leuco form and reduction of metal ions) of TiO₂–Bi₂O₃ materials were studied. Their catalytic activity was shown to be determined by their phase composition and structural perfection. The observed correlations between the properties studied are interpreted in terms of active sites for catalytic reactions.     

Phase equilibria in the RuO2−Bi2O3−CdO−Nb2O5 system

Interactions between the conductive phase in thick-film resistor materials (RuO₂ and Bi₂Ru₂O₇) and TCR modifiers (CdO and Nb₂O₅) were studied. Phase equilibria in the RuO₂−Bi₂O₃−CdO, RuO₂−Bi₂O₃−Nb₂O₅ and RuO₂−CdO−Nb₂O₅ systems were examined. The lines in the systems were established. The existence of a solid solution of composition Bi _2−x Cd _x Ru₂O _7−x/2 was confirmed.     

Optical absorption in co-evaporated V2O5-TeO2 thin films

The electron diffraction pattern shows that co-evaporated V₂O₅-TeO₂ thin film samples are amorphous at room temperature and become polycrystalline at temperatures higher than about 513 K. This behaviour is similar to that of amorphous V₂O₅ thin films. The optical absorption edge of amorphous thin films of V₂O₅-TeO₂ is studied in the wavelength range 200 to 900 nm and the FTIR spectra are studied in the wave number range 400 to 4000 cm^–1. The FTIR spectra of amorphous V₂O₅ thin film are found to be similar to those of amorphous V₂O₅-TeO₂ thin films. This suggests that the coordination number of the vanadium ion in V₂O₅-TeO₂ is the same as that in crystalline V₂O₅, and thus the optical absorption edge of amorphous V₂O₅-TeO₂ thin films can be described by direct forbidden transitions.     

Wetting of gold by Bi2O3-B2O3 melts

The wetting of gold by Bi₂O₃-B₂O₃ melts has been studied by the sessile drop method, with the sample and substrate heated separately before being brought into contact. Only the melts containing 18.5 and 33.3 mol % B₂O₃ were found to have steady-state contact angles.