title: Observations of Co4+ in a higher spin state and the increase in the Seebeck coefficient of thermoelectric Ca3Co4O9.
abstract: Ca3Co4O9 has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca3Co4O9 thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co4+-ions in a higher spin state compared to that of bulk Ca3Co4O9. The higher Seebeck coefficient makes the Ca3Co4O9 system suitable for many high temperature waste-heat-recovery applications.
authors.affiliation: Department of Physics, University of Illinois at Chicago, Chicago, Illinois, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Klie
authors.forename: Q
authors.initials: Q
authors.lastname: Qiao
authors.forename: T
authors.initials: T
authors.lastname: Paulauskas
authors.forename: A
authors.initials: A
authors.lastname: Gulec
authors.forename: A
authors.initials: A
authors.lastname: Rebola
authors.forename: S
authors.initials: S
authors.lastname: Öğüt
authors.forename: M P
authors.initials: MP
authors.lastname: Prange
authors.forename: J C
authors.initials: JC
authors.lastname: Idrobo
authors.forename: S T
authors.initials: ST
authors.lastname: Pantelides
authors.forename: S
authors.initials: S
authors.lastname: Kolesnik
authors.forename: B
authors.initials: B
authors.lastname: Dabrowski
authors.forename: M
authors.initials: M
authors.lastname: Ozdemir
authors.forename: C
authors.initials: C
authors.lastname: Boyraz
authors.forename: D
authors.initials: D
authors.lastname: Mazumdar
authors.forename: A
authors.initials: A
authors.lastname: Gupta