Strained ferroelectric NaNbO3 thin films: Impact of pulsed laser deposition growth conditions on structural properties

Pulsed laser deposition (PLD) was employed to grow coherent NaNbO3 thin films on several lattice matched substrates. Compressive (tensile) lattice strain was induced by the use of NdGaO3 and SrTiO3 (DyScO3 and TbScO3) single crystals. Deposition from a stoichiometric target at a 5 Pa O2 pressure was found to result in sodium and oxygen deficient films. By increasing the oxygen background pressure up to 200 Pa the oxygen and sodium concentrations in films on all substrates could be increased. As an alternative way to enhance the compositional ordering in the films sodium excess ceramics were used as PLD targets. With a Na/Nb ratio up to 1.17, phase pure, well-ordered films with smooth surfaces were grown on all substrates. The film composition was found to have a crucial impact on the formation of ferroelectric domains in tensilely strained films on DyScO3 substrates. Regularly arranged ferroelectric stripe domains were obtained at an oxygen partial pressure of 5 Pa using sodium rich growth parameters via the application of a 1.17 Na/Nb ratio PLD target.