Examining the structure and bonding in complex oxides using aberration-corrected imaging and spectroscopy

Origin of Phonon Glass–Electron Crystal Behavior in Thermoelectric Layered Cobaltate

“…Particularly, the real‐space measurement supports a clear analysis of the distribution of disordered and ordered crystallographic regions with subatomic accuracy. Strong atomic displacements are only present within the Ca 2 CoO 3 layer and not within the CoO 2 layer, in contrast to other reports based on reciprocal space methods, but in agreement with a recent STEM study published by Klie at al 28…”

“…This result contrasts with the claim in ref. 28 that the bonding between the CoO 2 and the Ca 2 CoO 3 layer is weak. Moreover, the CoO 2 ‐Ca 2 CoO 3 ‐interaction‐induced distortion destroys the spin and orbital ordering in the Ca 2 CoO 3 layer, resulting in some locally metallic‐like DOS in the band structure.…”

Improving the spin entropy by suppressing Co4+ concentration in thermoelectric Ca3Co4O9+

“…In this expression S, k, and s are the thermopower, the thermal conductivity and the electrical conductivity, respectively. Recently, layered cobalt oxide such as Ca 3 Co 4 O 9 þ d has been extensively investigated as promising candidates for p-type thermoelectric material due to its thermal and chemical stability at high temperature [3][4][5][6][7][8]. The misfit-layered cobalt oxide Ca 3 Co 4 O 9 þ d consists of two alternating subsystems, a CoO 2 sheet and a distorted rock-salt Ca 2 CoO 3 block stacked along the caxis, each fulfilling a different role in achieving prospective thermoelectric properties at high temperature.…”

Enhanced thermoelectric properties of Ca3Co4O9+δ by Ni, Ce co-doping

“…The efficiency of advanced thermoelectric technology of a material is determined by its figure of merit (ZT) ¼ S 2 T/ρκ, where T, S, ρ, and κ are the absolute temperature, thermopower, electrical resistivity, and thermal conductivity, respectively. Since Terasaki et al [2] reported that NaCo 2 O 4 features large thermopower and high electrical conductivity, layered cobalt oxides have been studied extensively [3][4][5]. Ca 3 Co 4 O 9 þ δ is considered a promising p-type thermoelectric material candidate because of its large thermopower, metallic conductivity, and chemical stability at high temperatures [6][7][8].…”