Fig. 1: Oxygen tracer exchange studies.

a 18O profiles determined by SIMS analysis for STNNi (donor-type) and b STNi (acceptor-type) after joint equilibration in 16O2 gas and subsequent exchange in 18O2 gas for different annealing times of t = 20 min, t = 100 min, and t = 200 min at T = 400°C and p(O2) = 200 mbar. The tracer fraction C’(x, t) incorporated into the thin film samples during oxygen exchange is plotted versus the sputter depth, respectively. A schematic illustration of the STNNi and STNi thin film samples is shown below respectively. STNNi exhibits a low oxygen vacancy concentration and slow correlated oxygen exchange kinetics, while STNi exhibits a large oxygen vacancy concentration and fast correlated oxygen exchange kinetics as denoted by the size and depth of the two arrows, respectively. Oxygen vacancies are depicted using circles.