Study of the ferroelectric properties of epitaxially strained SrTaO2N by means of DFT all-electrons first principles calculations.

M. TAYLOR; M. CAPPELLETTI; R.E. ALONSO

Cuenca

Congreso; XIII Reunión Nacional de Electrocerámica; 2017

SECV

Recently, ferroelectric behavior was observed in compressively strained SrTaO2N thin films epitaxially grown on SrTiO3 substrates. Piezoresponse force microscopy measurements revealed small domains (101 ?102 nm) that exhibited classical ferroelectricity, a behavior not previously observed in perovskite oxynitrides. The surrounding matrix region exhibited relaxor ferroelectric-like behavior, with remanent polarization invoked by domain poling. Bulk SrTaO2N samples do not show ferroelectricity, thus suggesting that the origin of it may be related with the strain induced by the substrate. Previous first-principles calculations suggested that the small domains and the surrounding matrix had trans-type and a cis-type anion arrangements, respectively, but do not address for the experimentally observed equilibrium phase, nor the strain dependent polarization. In this work, we present for the first time high accurate all-electron first-principles calculations on the different possible local structures that can explain the ferroelectric-like and relaxor properties of the strained material. The local structure and oxygen/nitrogen ordering has been related with polarization and epitaxial strain. We present the potential energies and polarization as functions of the in-plane lattice constant.