Tunable ferroelectric domain orientation in polycrystalline and highly oriented Na_0.5Bi_0.5TiO₃ Thin Films

Sodium bismuth titanate (Na_0.5Bi_0.5TiO₃: NBT) has shown promising piezoelectric properties as an alternate to lead based piezoelectrics. NBT films with preferred crystalline orientation along <220> and polycrystalline features were fabricated on commercially available (111) Pt coated Si substrates by pulsed laser deposition (PLD). Ferroelectric domain patterns of NBT film with preferred orientation along <220> exhibited a variable in-plane piezoresponse in comparison to the out-of plane response. The presence of dominating planar components of the spontaneous polarization (P_s<111>) of NBT with rhombohedral structure could be responsible for the difference in planar response with respect to the sample alignment. In addition, a coherent interaction between polarization vectors across the grains was observed. However, the piezocoefficient (d₃₃) measurements show that the oriented as well as polycrystalline film exhibits similar piezoresponse with an average value of ∼25 pm/V.