We report the laser irradiation-induced oxidation of bismuth metal investigated in situ by micro-Raman spectroscopy as a function of irradiation power and time. The purely optical synthesis and characterization of β-Bi2O3 oxide microislands on metallic Bi surfaces is shown to be stable over time, even at room-temperature. By closely examining possible reactions on simple Bi morphologies it is revealed for the first time that the ensuing oxide phase is critically dependent on the final oxide volume and follows a fixed kinetic transformation sequence: 32O2(g)+2Bi(l)→β–Bi2O3(s)→α–Bi2O3(s). These findings are unusual within the framework of traditional Bi2O3 thermal transformation relations. An electrostatic mechanism involving a changing Bi2O3 surface-to-volume ratio is proposed to explain the room-temperature metastability of small β-Bi2O3 volumes and the subsequent transformation sequence, as well as unifying the results of previous studies.

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In situ micro-Raman studies of laser-induced bismuth oxidation reveals metastability of beta-Bi2O3 microislands

Electrical conductivity of tetragonal β-phase (Bi2O3)1-x(Eu2O3)x (0.01 ≤ x ≤ 0.10 %mol) ceramic systems were investigated. The temperature and doping concentration dependences of the electrical conductivity were studied by four-point probe technique. The electrical conductivity increases with the increasing doping concentration and temperature. The highest value of the electrical conductivity is 0.013 Ω-1cm-1 (x = 0.05, 750 oC) for the β-phase at 670 oC and 0.57 Ω-1cm-1 (x=0.05, 800 oC) in binary systems at 690 oC. The phase transition which manifests itself by the jump in the conductivity curves was seen and verified by differential thermal analysis measurements. The activation energies of the samples were found to be about 0.71-1.57 eV.

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Electrical conductivity of the ionic conductor tetragonal (Bi2O3)1-x(Eu2O3)x

We have investigated Bi2O3-Eu2O3 binary system by doping with Eu2O3 in the composition range from 1 to 10 mole% via solid state reactions and succeeded to stabilize β-Bi2O3 phase which is metastable when pure. Stability of β-Bi2O3 polymorph was influenced by heat treatment temperature. Tetragonal type solid solution was obtained in 3–6 mole% addition range when annealed at 750°C and the range was 2–7 mole% when annealed at 800°C. We have also carried out investigations on lattice parameters, microstructural properties and elemental compositions of this β type solid solution for each doping ratio. Lattice parameters increased with amount of Eu2O3 addition. Our experimental observations strongly suggested that oxygen deficiency type non-stoichiometry is present in doped β type solid solutions.

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Synthesis and characterization of β type solid solution in the binary system of Bi2O3-Eu2O3

The total conductivity (σT) in bcc γ-Bi2O3 doped with V2O5 system has been measured in the composition range between 1 and 7 mol% V2O5 at different temperatures. Phase transitions for different addition amounts depending on the temperature were investigated by quenching the samples. According to the XRD and DTA/TG results, this bcc type solid solution was stable up to about 720°C and the solubility limit was found at ˜7 mol% V2O5 in γ-phase. This system showed predominantly an oxide ionic conduction. As the V2O5 addition increased, the ionic conduction increased up to 5 mol% V2O5 at which the highest conductivity was found to be 8.318·10-2 Ω-1 cm-1 at 700°C and then decreased. It has been proposed that γ-Bi2O3 phase contains a large number of oxide anion vacancies and incorporated vanadium cations at tetrahedral sites which affect the oxygen sublattice of the crystal structure.

Electrical conductivity of g-Bi2O3-V2O5 solid solution

In the present work, the binary system of (Bi2O3)1−x(Yb2O3)x was investigated. For the production and stabilization of the fcc-type solid solution, small amounts of Yb2O3 were doped into pure α-Bi2O3 by the solid-state reactions in the doping range of 0.10 ≤ x ≤ 0.2. According to XRD and electrical conductivity measurements, the crystal formula of the formed δ-Bi2O3 was found to be Bi(III)4−2xYb(II)2xO6−x□2+x (□: oxygen ion vacancies, VO··) and x values were in the range of 0.14 ≤ x ≤ 0.20 for heat treatment at 750 °C. Four-probe d.c. electrical conductivity measurements showed that the studied system had an O2− ionic-type electrical conductivity behavior. The maximum levels of the electrical conductivity were observed for 16 mol δ-YSB material which had σ
 T values: 0.316 and 0.632 Ω−1 cm−1 at 700 and 750 °C, respectively. These materials can be used as ceramic electrolytes for solid electrolytic industrial applications.

The bulk electrical conductivity properties of δ-Bi2O3 solid electrolyte system doped with Yb2O3

Electrical conduction in tetragonal β-Bi2O3 doped with Sb2O3 was investigated by measuring electrical conductivity, ionic transference number, and Seebeck coefficient. The β-Bi2O3 doped with 1 to 10 mol% Sb2O3 was stable up to 600°C and showed an oxygen ionic and electronic mixed conduction, where the electron conduction was predominant at low oxygen pressures. The oxygen-ion conductivity showed a maximum at 4 mol% Sb2O3, whereas the activation energy for the ionic conduction remained unchanged for 4 to 10 mol% Sb2O3-doped specimens. These results were interpreted in terms of the oxygen vacancy concentration and the distortion of the tetragonal structure. The electron conductivity and its oxygen pressure dependence decreased with increasing Sb2O3 content. The fact that Sb5+ is partially reduced by excess electrons in heavily doped β specimens at low oxygen pressures is explained.

Shinichi Katsuta

Papers

Electrical Conduction in β‐Bi2O3 Doped with Sb2O3