Crystallization, phase evolution and ferroelectric properties of sol–gel-synthesized Ba(Ti0.8Zr0.2)O3–x(Ba0.7Ca0.3)TiO3 thin films

Abstract

A lead-free piezoelectric material with ultra-high properties, Ba(Ti_0.8Zr_0.2)O₃–x(Ba_0.7Ca_0.3)TiO₃(BZT–xBCT) nanocrystals was synthesized via a sol–gel method, and the corresponding thin films were also deposited on Pt/Ti/SiO₂/Si substrates by a spin-coating approach. The BZT–xBCT thin film exhibited a high remnant polarization of 22.15 μC cm⁻² with a large coercive field of 68.06 kV cm⁻¹. The resultant gel is calcined at various elevated temperatures and studied with FTIR/XRD/Raman/DSC-TGA/AFM/SEM techniques for gel composition, crystallization, phase transition, thermochemistry and the morphology of the film. Although the room temperature crystal structure of the BZT–xBCT nanocrystals appears to be a standard perovskite structure by conventional X-ray diffraction (XRD), Raman spectroscopy demonstrates the presence of non-centrosymmetric regions arising from the off-centering of the titanium (zirconium) atoms. The Raman spectra findings demonstrate the degree by which the tetragonal phase grows with the increase of calcining temperature in BZT–0.5BCT, and the characteristic ferroelectric–ferroelectric phase transition in BZT–xBCT while going through the MPB process. The structural and constituent evolution for the conversion process from gel to ceramic, as well as the formation mechanism of the BZT–0.5BCT crystallite, were also elucidated.