Anion Order and Spontaneous Polarization in LaTiO₂N Oxynitride Thin Films

Vonrüti, Nathalie Simone; Aschauer, Ulrich Johannes (2018). Anion Order and Spontaneous Polarization in LaTiO₂N Oxynitride Thin Films. Physical review letters, 120(4), 046001-1-046001-5. American Physical Society 10.1103/PhysRevLett.120.046001

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The perovskite oxynitride LaTiO\textsubscript{2}N is a promising material for photocatalytic water splitting under visible light. One of the obstacles towards higher efficiencies of this and similar materials stems from charge-carrier recombination, which could be suppressed by the built-in electric field in polar materials. In this study, we investigate the spontaneous polarization in epitaxially strained LaTiO₂N thin films via density functional theory calculations. The effect of epitaxial strain on the anion order, resulting out-of-plane polarization, energy barriers for polarization reversal and the corresponding coercive fields are studied. We find that for compressive strains larger than 4\% the thermodynamically stable anion order is polar along the out-of-plane direction and has a coercive field comparable to other switchable ferroelectrics. Our results show that strained LaTiO₂N could indeed suppress carrier recombination and lead to enhanced photocatalytic activities.

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