TITLE:
CaCo1-xRuxOy: Role of Ru/Co Ratio on Its Transport Properties
AUTHORS:
Sezhian Annamalai, Rudra P. Bhatta, Jugdersuren Battogtokh, Ian L. Pegg, Biprodas Dutta
KEYWORDS:
Calcium Cobaltite; Ruthenium Oxide; Calcium Ruthenate; Transport Properties; Thermoelectric Properties; Seebeck Coefficient; Resistivity
JOURNAL NAME:
New Journal of Glass and Ceramics,
Vol.4 No.1,
January
27,
2014
ABSTRACT:
Calcium
cobaltites, especially Ca3Co4O9 with a misfit layered structure, are promising
thermoelectric materials due to their suitability for high temperature
applications and low densities. The
existence of low spin-state electronic configurations for both and species is one of the key parameter to explain the
large thermopower values. Ruthenium
oxide, with a layered structure, exhibits
strong electron-electron correlation and the extended nature of their 4d electrons
enhances orbital overlapping which is expected to influence the transport
characteristics of CaCo1-xRuxOy (CCR) samples,
by affecting the spin state of the 3d Co ions. The effect on thermopower
and electrical resistivity due to partial substitution of Co by Ru ions, up to 0.33 moles,
from 300 to 600 K was investigated. A sharp decline in resistivity and in thermopower
was observed until a transition ion ratio (TIR),
(Ru/(Ru + Co)), of 0.5 is reached, beyond which both the
properties became less sensitive to TIR.
These variations in the transport properties are explained by the presence of 4d Ru in close proximity to the Co, which could influence the spin and oxidation
state of Co ions. The Co rich and Ru rich samples exhibit very distinct
microstructures and phase assemblages.