Structural, Electronic, and Transport Properties of Thermoelectric Ca3Co4O9: Insights from First Principles Computations and Electron Microscopy
Abstract: Thermoelectric oxides have attracted increasing attention due to their high Seebeck coefficient and temperature stability. In particular, Ca3Co4O9 (CCO), a misfit-layered structure consisting of single layer hole-doped CoO2 sandwiched between insulating rock-salt type Ca2CoO3 layers exhibits a high Seebeck coefficient at 1,000 K. During the last few years, our Materials Modeling and Nanoscale Physics groups at UIC have been working in close collaboration to understand various properties of this interesting complex oxide and to increase its Seebeck coefficient. In this talk, I will present results and analyses of our combined synthesis/characterization/modeling studies on CCO. In particular, I will present (i) how we model this oxide with incommensurate subsystems from first principles using Fibonacci approximants, (ii) the importance of electron correlations in the two subsystems and their effects on the electronic and thermal properties, and (iii) how stacking faults with Co4+ -ions in a higher spin state result in a significant increase in the Seebeck coefficient of 40 nm thick CCO films grown by pulsed laser deposition on SrTiO3 substrates.