Single crystalline Sn2Nb2O7 films with Ti-doping fabricated by pulsed laser deposition

Sn2Nb2O7, a pyrochlore oxide, is expected to have a peculiar flat band structure that can be a source of intriguing physical properties. We have prepared Sn2Nb2O7 thin films by pulsed laser deposition on Y-stabilized ZrO2(111) substrates by finding a growth window at low growth temperature (∼450 °C) and higher laser fluence, possibly due to the rather high volatility of stannous oxide. By Ti-doping, the lattice constant shrinks due to the smaller Ti4+ ion compared with Nb5+. Optical measurements capture an absorption edge at ∼2.6 eV originating from the transition from the Sn-5s and O-2p hybridized valence band to the Nb-4d conduction band, which is not observed in LiNbO3. Opposed to the expectation from the Burstein–Moss shift, Ti-doping results in reduction of the bandgap, indicating that the doping results in the formation of in-gap states and does not contribute to injecting mobile carriers.