Doping mechanisms and electrical properties of bismuth tantalate fluorites

Abstract

Phase-pure bismuth tantalate fluorites were successfully prepared via conventional solid-state method at 900 °C in 24-48 h. The subsolidus solution was proposed with the general formula of Bi3+x Ta1−x O7−x (0 ≤ x ≤ 0.184), wherein the formation mechanism involved a one-toone replacement of Ta5+ cation by Bi3+ cation within ~4.6 mol% difference. These samples crystallised in a cubic symmetry, space group Fm-3 m with lattice constants, a = b = c in the range 5.4477(± 0.0037)-5.4580(± 0.0039) Å. A slight increment in the unit cell was discernible with increasing Bi2O3 content, and this may attribute to the incorporation of relatively larger Bi3+ cation in the host structure. The linear correlation between lattice parameter and composition variable showed that the Vegard's law was obeyed. Both TGA and DTA analyses showed Bi3+x Ta1−x O7−x samples to be thermally stable as neither phase transition nor weight loss was observed within ~28-1000 °C. The AC impedance study of Bi3TaO7 samples was performed over the frequency range 5-13 MHz. At intermediate temperatures, ~350-850 °C, Bi3+x Ta1−x O7−x solid solution was a modest oxide ion conductor with conductivity, ~10−6-10−3 S cm−1; the activation energy was in the range 0.98-1.08 eV.

Identification of distinctive structural and optoelectronic properties of Bi2O3 polymorphs controlled by tantalum addition

“…However, the charge has been reasonably explained to be balanced by the change in the occupancy of O sites in previous studies. 5 Therefore, it can be concluded that by mixing Bi 2 O 3 and Ta 2 O 5 at a molar ratio of Ta/Bi = 0.1, 0.33, the resulting Bi–Ta oxides stabilized and formed a substitutional solid solution with the cubic crystal phase.…”

“…Bi 2 O 3 is one of the polymorphous oxides, and is employed in a broad range of applications such as solid-state electrocatalysis, [1][2][3][4][5][6] inorganic orange pigment, 7 and photocatalytic reactions. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] To date, four different crystal phases have been reported: a phase (monoclinic), b phase (tetragonal), g phase (cubic), and d phase (cubic).…”

“…The high-temperature-stable d phase is transformed into the b or g phase while cooling, which results in the further transformation into the a phase at room temperature. 28 While the d phase shows a high O 2À ion conductivity, applicable to mid-temperature electrocatalysis at 300-500 1C, [1][2][3][4][5] b-Bi 2 O 3 attracts attention as a photocatalyst due to a narrow bandgap of B2.2 eV. [8][9][10][11][12] Solid-state synthesis of pure Bi 2 O 3 has been well reported in the literature.…”

“…Nevertheless, selective synthesis of specific phases from pure Bi 2 O 3 remains challenging. By doping a-Bi 2 O 3 with a trace amount of oxides, such as Ta 2 O 5 , CeO 2 , ZrO 2 , EuO x , TiO x , and MnO x , 5,7,[29][30][31][32][33] a solid-state reaction at a high temperature becomes possible to make metastable b-, g-, and d-phases recoverable for successive applications. Recently, Masui and coworkers reported the addition of Ta 2 O 5 into a-Bi 2 O 3 to synthesize band d-phases, and among them, b-Bi 2 O 3 was recognized to have a potential to be a orange pigment with its vivid orange color due to its unique bandgap narrowing.…”

Synthesis and Properties of Vanadium Substituted Bismuth Tungstates with Fluorite-like Structure

“…For this purpose, substitution with various suitable ions (Nb 5+ , Mo 6+ , Ta 5+ , Ti 4+ , W 6+ etc.) is usually used [1][2][3][4]. It is found for Bi 2 O 3 -WO 3 system that the introduction of tungsten oxide (more than 9 wt.%) is a necessary condition for stabilization of δ-phase Bi 2 O 3 [5].…”