Oxidation states and thermoelectric properties of BiCuSeO bulks fabricated under Bi or Se deficiencies in the nominal composition

Abstract

We have fabricated the BiCuSeO bulks using raw materials with Bi or Se deficiencies in the nominal composition and investigated crystallographic, chemical compositional, and thermoelectric properties. Owing to the Bi or Se deficiencies in the starting composition, excessive elements and related compounds were deposited as impurity phases and the matrix phase is nearly the stoichiometric BiCuSeO phase. The electrical resistivity, q(T), of the bulks decreases and thermoelectric power, S(T), also decreases with increasing the contents of Bi or Se deficiencies in the starting composition in spite of the stoichiometric matrix phase. These results strongly suggest that, from the X-ray photoelectron spectroscopy measurements, the actual oxidation states of Bi and Cu deviate from the formal valences of stoichiometric Bi 3þ Cu 1þ Se 2À O 2À . The introduction of a small amount of Bi and Se vacancies is also suggested. As a result, mobile carriers are introduced and the q and S values are changed. The maximum thermoelectric dimensionless figure of merit of ZT ¼ 0.60 was achieved at 773 K for the Bi 1-x CuSeO samples (x ¼ 0.025 and 0.05) in the starting composition. These results are in clear contrast with the reported results for the Cu deficiency bulks. Using these results, we propose charge valence equations and the origin of the carriers in the present BiCuSeO bulks and discuss the influence of created carriers on the thermoelectric properties.Published by AIP Publishing. https://doi.

Influence of Bi Substitution with Rare-Earth Elements on the Transport Properties of BiCuSeO Oxyselenides

“…On the other hand, a noticeable amount of impurity phases, Cu 2– x Se (PDF#01-074-1373) and Bi 2 O 3 (PDF#01-088-2043), in the Bi 1– x R x CuSeO samples fabricated with ball milling were detected, they account for less than 3 and 5 vol %, respectively. The appearance of these impurity phases in the samples with ball milling may be a result of Bi or/and Cu deficiency formation as was previously reported. ,, The unit cell parameters for the pristine sample prepared without ball milling are a = 3.92710 Å and c = 8.9278 Å. These values are in good agreement with those reported for samples synthesized by a conventional two-step solid-state reaction .…”

“…The appearance of these impurity phases in the samples with ball milling may be a result of Bi or/and Cu deficiency formation as was previously reported. 30,44,45 The unit cell parameters for the pristine sample prepared without ball milling are a = 3.92710 Å and c = 8.9278 Å. These values are in good agreement with those reported for samples synthesized by a conventional two-step solid-state reaction.…”

“…Moreover, the carrier concentration of all the samples increased with increasing temperature due to the thermal excitation. The charge carrier density in BiCuSeO may be affected by various crystal defects, such as anti-site defects, 50 deviations from nominal oxidation states, 44,51 or vacancies 47,52 as it was previously reported for oxychalcogenide-based compounds. 53−56 Although the role of defects in this system requires further detailed studies, it is clear that the enhanced electrical conductivity of the BM BiCuSeO and that of the substituted samples should be attributed to the increased charge carrier density (see Table 3).…”

Effect of Foliar Sodium Selenate on Leaf Senescence of Fragrant Rice in South China

“…Selenium (Se) is an essential element to humans, animals and plant. Se deficiency had been associated with poor immune function, increased risk of mortality, and cognitive decline (Yang et al, 2018;Ishizawa et al, 2018). The research of Lee even revealed that Se could be a cancer-protective agent (Lee, 1996).…”

Влияние лантана на транспортные свойства оксиселенидов Bi-=SUB=-1-x-=/SUB=-La-=SUB=-x-=/SUB=-CuSeO

“…Температурная зависимость подвижности носителей заряда для Bi 1−x Lax CuSeO (x = 0.02, 0.04, 0.06). На вставке -температурная зависимость подвижности в координатах µ − T1.5 .По нашему мнению, такое изменение транспортных свойств Bi 1−x La x CuSeO может быть обусловлено возникновением дополнительных вакансий висмута при его замещении лантаном, как это было показано в других работах[22][23][24][25]. Наряду со снижением энергии формирования вакансий Bi при допировании исходного соединения (см., например,[25]) наличие фазы CuSe также может…”