Effect of semiconductor to metal transition on thermoelectric performance in oxide nanocomposites of SrTi0.85Nb0.15O3 with graphene oxide

Enhanced Thermoelectric Performance in Oxide Composites of La and Nb Codoped SrTiO3 by Using Graphite as the Electron Mobility Booster

“…Here, a B is the Bohr radius and n is the critical carrier concentration required for S–M transition. This kind of Mott transition has already been reported in many oxide perovskites. ,,− It is possible that using codoping in STO and processing steps such as repeated calcination in a reducing atmosphere, nanomilling can generate a significant amount of defects and lattice strain, which render the electrons to be localized. This localization of the carrier is known as Anderson localization. − Anderson localization can be conceded as one of the possible explanations behind the oppressive electrical conductivity in pristine LSTN, which does not get reflected in the Hall measurement data .…”

“…It has been observed by researchers that chemical doping alone cannot increase ZT values significantly in STO due to interdependent thermoelectric parameters. A composite route, especially with carbon-based materials such as r-GO, GO, graphite, and so forth has been proven to be a successful strategy to enhance ZT . − In recent years, r-GO has been widely used to form a composite with doped STO demonstrating some of the excellent thermoelectric results among the n-type bulk oxide thermoelectrics. − The primary role of 2D graphene has been proposed to be enhancing the electron mobility by refining grain boundaries, which otherwise possess a highly resistive double Schottky barrier. ,, Due to depletion of oxygen vacancies at the grain boundary regions, this highly resistive Schottky barrier is formed in polycrystalline oxide, which is further reduced due to the presence of 2D graphene as it promotes the formation of more oxygen vacancies. , As a result, single-crystal-like electron mobility is achieved in STO-based ceramics. − , Although the concept of grain boundary engineering by highly conductive 2D materials such as graphene seems to be quite convincing, it always raises the concern whether it is the sole reason for observing single-crystal-like charge transport in spite of using a very small quantity (<1 wt %) of graphene, which may not cover the omnipresent grain boundaries in polycrystalline ceramics. Recently, Acharya et al have reported ZT = 1.42 in the composite of Nb-doped STN with graphite, which infers a significant breakthrough in the field of oxide thermoelectrics for attaining the highest ever ZT among n-type oxide thermoelectrics .…”

Key properties of inorganic thermoelectric materials—tables (version 1)

“…Increased zT values, around 0.4 were achieved over a wide temperature range up to 873 K, thereby greatly enhancing the operational thermal window. Other studies with graphene/graphene oxide support the enhancement behavior [605][606][607]609]. It is predicted that zT values above 0.5 could be achieved for STO-graphene composites by optimizing the grain boundary structure [671].…”

“…By processing under reducing conditions a high PF, comparable with that of Bi 2 Te 3 can be achieved, but reducing thermal conductivity is much more of a challenge as nanostructuring is less effective than in many other materials. Doping on the cation A site, with La in place of ∼10% of the Sr has been popular and effective, which under reducing conditions leads to the formation of oxygen vacancies, which enhance electrical conductivity and reduce thermal conductivity [596][597][598][599][600][601][602][603][604][605][606][607][608][609][610][611][612]. On the cation B site, doping with higher valent Nb leads to metallic conduction and simultaneously increases S because the effective mass m * is increased; consequently, the PF σS 2 is enhanced, with values of ∼1500 µW m −1 K −2 at 1000 K recorded for SrTi 0.8 Nb 0.2 O 3 epitaxial films and a zT max of 0.37 [596].…”

Superior thermoelectric properties of ternary chalcogenides CsAg5Q3 (Q = Te, Se) predicted using first-principles calculations

“…Therefore, in order to maximize ZT for advancing thermoelectric devices with high efficiency, one should increase the thermopower factor (PF = S 2 σ ) and/or lower the thermal conductivity. This can be achieved by tailoring new TEMs using various strategies such as band engineering, 8,9 nanostructuring, 10–12 and alloying or substituting. 13–18…”