Low-temperature electrodeposition of the high-temperature cubic polymorph of bismuth (III) oxide (original) (raw)
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Journal of the Ceramic Society of Japan, 2010
Epitaxial xBi(Zn 1/2 Ti 1/2)O 3 (1 ¹ x)BiFeO 3 films were grown on (100) c SrRuO 3 ==(100)SrTiO 3 substrates by metal organic chemical vapor deposition (MOCVD). The effects of x value on the crystal structure and the electrical properties were investigated. Constituent phase changed from rhombohedral symmetry to two types of tetragonal ones with different unit cell volume and tetragonality. Rhombohedral phase and the tetragonal phase with smaller tetragonality were not ascertained to transform to cubic phase up to 800°C from high temperature XRD results. Relative dielectric constant measured at room temperature showed the maximum value at x = 0.21 near the phase boundary between tetragonal and rhombohedral symmetries. Leakage current became small when the measurement temperature decreased at 80 K and the ferroelectricity monotonously decreased with increasing x values and was not ascertained above 0.26.
Polymorphism and Electrical Properties in the New Oxide Bi 6 Mo 2 O 15
A new oxide of composition Bi 6 Mo 2 O 15 has been isolated in the binary system Bi 2 O 3 -MoO 3 . A wet-chemistry procedure, different from coprecipitation, has been used to prepare a nanosized, very reactive precursor. Annealing at different temperatures and for different time lengths leads to isolated polycrystalline polymorphs. X-ray powder diffraction studies on the hitherto unknown low-temperature form, L-Bi 6 Mo 2 O 15 , show that it crystallizes in the monoclinic system, with unit-cell parameters a ) 29.0674(5) Å, b ) 5.64795(7) Å, c ) 8.6620(1) Å, ) 97.979(1)°, and V ) 1408.3 Å 3 . The high-temperature polymorph, H-Bi 6 -Mo 2 O 15 , belongs to the well-known [Bi 12 O 14 ] columnar structural type. The relationship between the unit-cell parameters of both phases points at the connection of their structural frameworks. Impedance spectroscopy measurements show that the transition LTH-Bi 6 -Mo 2 O 15 is partially reversible, as well as the existence of a second high-temperature phase H′, similar to H. In contrast, the transition HfH′-Bi 6 Mo 2 O 15 is not reversible. These materials turn out to be good ionic conductors, with conductivities in the order L < H < H′ for all temperatures tested.
Chemistry of Materials, 1996
A series of Bi 2 O 3-based oxides of general formula Bi 2-2x U x La x O (3+3x/2) (0.333 g x g 0.038) has been synthesized by two different methods. Materials were characterized by X-ray diffraction, chemical analysis, X-ray photoelectron spectroscopy, and thermal analysis. X-ray diffraction data show that they crystallize with cubic or hexagonal symmetry depending on composition and synthesis procedure. In particular, the stabilization of the fluorite-type structure as a single phase at room temperature has been achieved in the compositional range 0.154 g x g 0.091. The annealing of materials at 600°C for 500 h yields in all cases a "tetragonal" phase that is isolated as the only phase for x) 0.222. The evolution of this phase with temperature has been studied. Aged materials can be regenerated when they are subjected to the original synthesis conditions.
Insights into the Electrodeposition of Bi2Te 3
2002
In this paper, the processes associated with the electrodeposition of bismuth telluride (Bi 2 Te 3 ), a thermoelectric material, are reported along with an analysis of the composition and crystallinity of the resulting films. The electrodeposition can be described by the general reaction 3HTeO 2 ϩ ϩ 2Bi 3ϩ ϩ 18e Ϫ ϩ 9H ϩ → Bi 2 Te 3 ϩ 6H 2 O. Cyclic voltammetry studies of Bi, Te, and Bi/Te dissolved in 1 M HNO 3 reveal two different underlying processes depending on the deposition potential. One process involves the reduction of HTeO 2 ϩ to Te 0 and a subsequent interaction between reduced Te 0 and Bi 3ϩ to form Bi 2 Te 3 . A second process at more negative reduction potentials involves reduction of HTeO 2 ϩ to H 2 Te followed by the chemical interaction with Bi 3ϩ . Both processes result in the production of crystalline Bi 2 Te 3 films in the potential range Ϫ0.1 Ͻ E Ͻ Ϫ0.52 V vs. Ag/AgCl ͑3 M NaCl͒ on Pt substrates as determined by powder X-ray diffraction ͑XRD͒. Electron probe microanalyses and XRD reveal that the films are bismuth-rich and less oriented for more negative deposition potentials.
A solution chemistry approach to epitaxial growth and stabilisation of Bi 2 Ti 2 O 7 films
J. Mater. Chem. A, 2014
Single crystalline pyrochlore Bi 2 Ti 2 O 7 films have been grown in three different orientations on yttria-stabilised zirconia at temperatures as low as 600 C, by using a simple wet chemistry method based on the spin-coating technique. Contrary to free-standing powders and polycrystalline films, epitaxial single crystalline Bi 2 Ti 2 O 7 is stable relative to other bismuth titanate compounds at temperatures up to 900 C. A study of core X-ray photoelectron spectra shows Bi 2 Ti 2 O 7 films contain an oxygen deficiency whose concentration depends on the annealing temperature. Based on low-energy ion scattering spectroscopy, it was determined that crystalline surfaces terminate in BiO xlike structures. † Electronic supplementary information (ESI) available: ESI contains experimental details, X-ray diffractograms of Bi 2 Ti 2 O 7 lms deposited on (111)-oriented YSZ at 600 C, 750 C and 900 C, and LEIS spectra of all crystalline surfaces studied in this work. See
In this study; production and characterization of Bi 2 O 3 based solid electrolytes used in medium-temperature solid oxide fuel cells (IT-SOFC) were performed. Solid electrolyte samples were obtained using compounds Eu 2 O 3 , Dy 2 O 3 and Bi 2 O 3. Stable phase which can create the highest power density δ-Bi 2 O 3 (cubic-fcc) was tried to be reached for IT-SOFC. X-ray diffractometry (XRD) and differential thermal analysis and thermal gravimeter (TG/DTA) with binary (Eu 2 O 3-Bi 2 O 3) and ternary (Eu 2 O 3-Dy 2 O 3-Bi 2 O 3) powder materials were analyzed for crystal structure identification. Bi 2 O 3-based compounds with the cubic structure have been identified in those composition regions ((Bi 2 O 3) 0,6 (Eu 2 O 3) 0,3) and ((Bi 2 O 3) 1-x-y (Dy 2 O 3) x (Eu 2 O 3) y , 0.25 ≤ x ≤ 0.35, y=0,05). Four point measurement techniques were used for electrical characterization. The conductivity of the ternary system is higher than the conductivity of the binary system. The highest conductive sample is (Bi 2 O 3) 0,7 (Dy 2 O 3) 0,25 (Eu 2 O 3) 0,05 0.3 S/cm at 800 o C.
New Structural and Electrical Data on Bi–Mo Mixed Oxides with a Structure Based on [Bi12O14]∞Columns
Journal of Solid State Chemistry, 1999
We recently described a new family of oxide anion conductors with a structure based on [Bi 12 O 14 ] columns (J. Solid. State Chem. 122, 394 (1996)). The parent compound of this series can be formulated as Bi 26 Mo 10 O 69 and formation of a solid solution, in the Bi 2 O 3-MoO 3 binary system, in the range 2.574 Bi/Mo42.77 was established. The stoichiometry of this series was questioned by R. Enjalbert et al. (J. Solid State Chem. 131, 236 (1997)), but confirmed by D. J. Buttrey et al. (Mater. Res. Bull. 32, 947 (1997)). The first part of this paper is devoted to a refutation criticisms by R. Enjalbert et al. In the second part, a comparison with other Bi 2 O 3-based oxide anion conductors enables us to propose an iono-covalent description of this novel structure type, taking into account all the structural and electrical features, especially new neutron powder diffraction refinement and conductivity measurements under variable oxygen partial pressures.