Hydrothermal synthesis of lead free piezoelectric materials

Abstract

This thesis reports successful synthesis of NKN solid solution powder series with compositions around the morphotropic phase boundary (MPB) hydrothermally at 200°C using a simple KOH and NaOH mixture with Nb2O5 as a precursor powder. Hydrothermal synthesis route adds the green-synthesis advantage to the already less toxic NKN by enabling growth at low temperatures (≤200°C, way below NKN Curie temperature), in water using simple chemicals and recyclable process. More significantly, this thesis demonstrates that the NKN solid solutions can be grown epitaxially over a conductive substrate using the same procedure. Thorough structural studies of hydrothermally grown NKN films and powders described in this thesis have shed light on the significant role of lattice trapped –OH related defects to the films’ electrical properties, crucial in devising strategies to remove the defects effectively and improve the ferro/piezoelectric performance. This thesis envisions to make widespread usage of I-V perovskite based lead-free ferro/piezoelectric materials a step closer to reality and shift the heavy reliance towards the high temperature, energy and labor intensive solid-state based materials synthesis.