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Epitaxial a-axis oriented NaNbO3 films are grown on (110) oriented NdGaO3 substrates. The lattice mismatch between substrate and film leads to compressive strain of ∼0.7% in the a-c plane. As a consequence, the in-plane permittivity and tunability are strongly enhanced compared to bulk NaNbO3, and a pronounced maximum in the temperature dependence of the permittivity occurs. Below the maximum at Tmax ≈ 250 K, ferroelectric behavior is observed that seems to vanish above Tmax. The pristine phase of the film at T < Tmax is antiferroelectric and is easily suppressed by small applied electric fields. The ferroelectric phase shows a relaxor type behavior.

The electrical behavior of iron‐doped strontium titanate (Fe:SrTiO3) single crystals equilibrated at 900°C and quenched below 400°C at various oxygen partial pressures (PO2) was investigated via impedance spectroscopy and compared to defect chemistry models. Fe:SrTiO3 annealed and quenched between 1.2 × 10−14 and 2.0 × 10−4 Pa PO2 exhibits a conduction activation energy (EA) around 0.6 eV, consistent with ionic conduction of oxygen vacancies. However, sudden changes in EA are found to either side of this range; a transition from 0.6 to 1 eV is found in more oxidizing conditions, while a sudden transition to 1.1 and then 0.23 eV is found in reducing PO2 These transitions, not described by the widely used canonical model, are consistent with predictions of transitions from ionic to electronic conductivity, based on first principles point defect chemistry simulations. These models demonstrate that activation energies in mixed conductors may not correlate to specific conduction mechanisms, but are determined by the cumulative response of all operative conduction processes and are very sensitive to impurities. A comparison to electrically degraded Fe:SrTiO3 provides insight into the origins of the conductivity activation energies observed in those samples.

Dielectric and ferroelectric properties of ( Na 0.8 K 0.2 ) 0.5 Bi 0.5 TiO 3 thin films prepared by metalorganic solution deposition Appl. Phys. Lett. 87, 192901 (2005) Epitaxial c-axis oriented NaNbO 3 films are grown on (110) oriented NdGaO 3 substrates. Due to the incorporated lattice strain the films show relaxor ferroelectric properties and an in-plane permittivity that is strongly enhanced with respect to unstrained NaNbO 3 . Moreover, the lattice mismatch between substrate and film leads to an anisotropy in the compressive in-plain strain of À0.67% and À1.33% for the a-and b-direction of the films, respectively. As a consequence, the ferroelectric properties of the film depend strongly on the orientation of the applied electric field. The small anisotropy of the compressive in-plane strain leads to a large anisotropy of the permittivity, a shift of the peak in the temperature dependence of the permittivity, and different freezing temperatures and activation energies E a of the relaxor ferroelectric film. V C 2014 AIP Publishing LLC.