The Seebeck Coefficient in Oxygen Enriched La$_2$NiO$_4$

Oxide-based devices show promise for themoelectric applications due to their chemical stability and straightforward fabrication. The La$_2$NiO$_{4+\delta}$ system has been predicted to show an increased thermopower coupled with an increased electrical conductivity around $\delta=0.05$ [Pardo et al. PRB 86, 165114 (2012)] that could lead to a large thermoelectric figure of merit (ZT). We investigate the suitability of lanthanum nickelate as a candidate material for high-ZT devices through a systematic study of oxygenated thin films grown by pulsed laser deposition. We report the electrical conductivity, Seebeck coefficient, and structural morphology of La$_2$NiO$_4$ grown in a range of oxidizing atmospheres and discuss their implications for controlled engineering of thermoelectric properties. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovaci\'on (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS.