Spontaneous superlattice formation and thermoelectric properties of A-site excess (La, Sr)CoO3 thin films prepared using dynamic aurora pulsed laser deposition

Periodic nanomaterials like superlattices find extensive use in diverse applications. Epitaxial growth has been extensively recorded in semiconductors, leading to the spontaneous formation of layer structures. However, this phenomenon is almost not observed in ceramics. In this study, we aimed to form the spontaneous superlattice of (La, Sr)CoO3 thin films having an A-site excess by dynamic aurora PLD method with the presence of magnetic field. The spontaneous superlattice was formed by varying several parameters (magnetic field, annealing oxygen pressure, and A/B ratio) in pulsed laser deposition (PLD), and its thermoelectric properties were studied. The (La, Sr)CoO3 spontaneous superlattice was successfully formed by depositing the thin film under an applied magnetic field ranging from 100 to 200 mT. Moreover, thin film A-site excess composition was optimized around A/B = 1.2 to 1.4 in atomic ratio and the in-plane lattice parameter of the thin film coincided with the substrate. The presence of a satellite peak of (La1-xSrx)CoO3 was observed by the XRD analysis, providing confirmation of the formation of a superlattice, and its superlattice period was calculated. The thermoelectric measurement was performed for (La, Sr)CoO3 thin films with a superlattice period of 12 nm and exhibited the maximum Seebeck coefficient was about 28.4 mu VK-1 at 880 K. The electrical conductivity was obtained as 50 Scm(-1) at 850 K due to the higher density of states in the valence band near E-F. Moreover, the decreasing trend of the Seebeck coefficient was observed with an increasing superlattice period due to the presence of oxygen vacancy that occurred by the PLD deposition under the low annealing oxygen pressure. The power factor was calculated as 2.3 mu Wm(-1)K(-2) at 783 K. This measurement demonstrates the thin film's adequate capacity to conduct electric current.