Electronic transport and thermoelectric properties of RBaCo4O7 (R=Dy, Ho, Y, Er)

The electrical resistivity and Seebeck coefficients of RBaCo4O7 (R=Dy, Ho, Y and Er) were measured in the temperature range 350–1000 K. It was found that all compositions behave as p-type semiconductors in the temperature range measured. The calculated activation energy of conductivity is larger than that of thermopower in the temperature range of 350–650 K, which means that the conduction mechanism may be determined as a small polaron hopping model. The conduction mechanism may be changed when temperature is above 650 K due to a possible change in symmetry or/and the release of oxygen from crystal lattices. The power factors (S2/ρ) increase with the increase of temperature and the maximum value of YBaCo4O7 at 1000 K is 4.9×10−5 W m−1 K−2 that is comparable to that of Ca3Co4O9.