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First‐principles Studies of the Electronic and Thermoelectric Properties of Misfit Layered Phases of Calcium Cobaltite
Author(s) -
Ramasubramaniam Ashwin
Publication year - 2017
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.201600065
Subject(s) - cobaltite , seebeck coefficient , thermoelectric effect , condensed matter physics , chemistry , thermoelectric materials , phase (matter) , doping , fermi level , electronic structure , semiconductor , materials science , thermodynamics , optoelectronics , computational chemistry , electron , physics , organic chemistry , quantum mechanics
The electronic and thermoelectric properties of two phases of calcium cobaltite, a misfit layered compound, are investigated and compared using first‐principles DFT calculations. The two phases considered here include the conventional bulk phase that consists of alternating layers of Ca 2 CoO 3 and CoO 2 , and a new phase that consists of alternating layers of CaCoO 2 and CoO 2 , which was recently discovered in nanotubes. Electronic structure calculations reveal that both phases are ferrimagnetic materials with one important difference: the bulk phase is metallic, whereas the nanotubular phase is semiconducting. The metal‐to‐semiconductor transition that accompanies the Ca 2 CoO 3 to CaCoO 2 structural transition is shown to arise from the depletion of free carriers from the donor Ca atoms. The implications of the difference in electronic structure for the thermoelectric performance of these two phases are further examined with Boltzmann transport calculations. Relative to the metallic phase, the semiconducting phase displays appreciably higher Seebeck coefficients at minimal doping levels; these increased Seebeck coefficients compensate for the reduced conductivity and result in large power factors. In conjunction with the fact that the semiconducting phase is peculiar to 1D nanotubes, it is expected that additional effects from quantum confinement could render these low‐dimensional materials as promising thermoelectric materials.