Lead-free ferroelectric films by pulsed laser deposition

Abstract

Lead-based ferro/piezoelectric materials, such as Pb(Zr0.52Ti0.48)O3, are widely used because of their excellent ferroelectric and piezoelectric properties near the morphotropic phase boundary. However, due to the environmental concerns associated with lead, alternative lead-free ferro/piezoelectric systems are highly demanded. Extensive research has been conducted in this direction and several promising candidates have been identified. This dissertation details our efforts in this area.

The primary work described herein are the synthesis and characterizations, in thin film form, of two promising candidates, [(K0.5Na0.5)0.97Li0.03](Nb0.8Ta0.2)O3 (KNN-KNT-L0.03T) and Bi(1-x)LaxFeO3 (x=0, 0.05, 0.10, 0.15 and 0.20). The textured polycrystalline KNN-KNT-L0.03T ceramic at morphotropic phase boundary composition exhibits piezoelectric coefficient larger than that of Pb(Zr0.52Ti0.48)O3 ceramic. However, from application point of view, it is desirable to study its properties in thin film form. Epitaxial films of KNN-KNT-L0.03T are fabricated on (001), (110) and (111)-cut single crystal SrTiO3 substrates by pulsed laser deposition, which allow us to study the intrinsic properties along different crystallographic directions. The crystal structure and electrical properties are investigated and the structure-property relationship is established. BiFeO3 is another promising candidate as it possesses the largest switchable polarization observed so far in any perovskite ferroelectric material. It is also the only known single-phase multiferroic that simultaneously show both antiferromagnetic and ferroelectric orders at room temperature. BiFeO3 holds great promise for novel non-volatile memories, spintronic devices and as a lead-free ferro/piezoelectric material.