Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites

The Hall coefficient R-H and electrical conductivity of misfit calcium cobalt oxide (Ca2CoO3-delta)(q)(CoO2) (CCO) were measured at room temperature for different oxygen vacancy concentrations delta. Based on these and numerous previous results, it is shown that the charge carrier concentrations n obtained by the classical formula R-H = 1/ne are between 3 and 6 x 10(20) cm(-3) and thereby much lower than those derived by other experimental techniques and fail to explain the observed electric properties of CCO. We show that the experimental results are well described using an earlier proposed t-J-model for strongly correlated electrons on a triangular lattice. The hopping parameter t for CCO was found to be approximate to -20K and the charge carrier concentration of fully oxidized CCO to be 5.7 x 10(21) cm(-3) (0.41 hole type carriers per formula unit), in agreement with other experimental techniques. (c) 2015 AIP Publishing LLC.