Synthesis Of Bi1 Research Articles

Structure and Thermoelectric Properties of Nanostructured Bi1−xSbx Alloys Synthesized by Mechanical Alloying

We report on the synthesis of Bi1−xSbx alloys and the investigation of the relationship between their structural and thermoelectric properties. In order to produce a compound that will work efficiently even above room temperature, Bi1−xSbx alloys were chosen, as they are known to be the best suited n-type thermoelectric materials in the low-temperature regime (200 K). Using a top–down method, we produced nanostructured Bi1−xSbx powders by ball-milling in the whole composition range of 0 < x < 1.0. Nanostructuring of Bi1−xSbx alloys increases the band gap and thus results in an enlargement of the semiconducting composition region (0 ≤ x ≤ 0.5) compared to its bulk counterpart (0.07 ≤ x ≤ 0.22). The enhancement of the band gap strongly affects the transport properties of the alloys, i.e. the electrical conductivity and the Seebeck coefficient. Moreover, nanostructuring reduces the thermal conductivity through the implementation of grain boundaries as phonon-scattering centers, leading to a significant enhancement of the thermoelectric properties. The highest figure-of-merit observed in this study is 0.25 which was found for Bi0.87Sb0.13 at 280 K.

Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO3 doped by Sr2+ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi1−x Sr x FeO3−δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO3 is 1046 K, whereas the substitution of 20 mol% of Bi3+ by Sr2+ ions shifted it to 1403 K and powder with composition Bi0.65Sr0.35FeO3−δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi0.85Sr0.15FeO3−δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).