Optimization of the production process of BZT–BCT sol–gel thin films obtained from a highly stable and green precursor solution

Barium Zirconate Titanate–Barium Calcium Titanate (BZT–BCT) is an environmentally friendly piezoelectric-ferroelectric ceramic that is a promising alternative to lead zirconate titanate (PZT), whose toxicity is well known. Producing thin films by sol–gel deposition with properties comparable to their bulk counterparts is quite a difficult task, because of the substrate constraints which typically generate residual stresses during the production process, leading to the onset of cracks. Moreover, typically employed solutions contain toxic and harmful substances or are unstable over time. Recently, we produced a highly stable BZT–BCT precursor solution based on nontoxic and non-carcinogenic solvents. In this work, we optimized the BZT–BCT sol–gel deposition process by varying the spin coating velocity, which influences the thickness of each deposited layer, and the pyrolysis temperature, which impacts on the formation of cracks. Moreover, we explored the possibility to add a third heat treatment step to the deposition process with the aim of releasing the residual stresses, further improving the film properties. As a result, 250 nm thick films were obtained with optimized morphology and limited presence of cracks, thus enhancing the ferroelectric properties (Pr = 33.26 μC cm−2, Ec = 220.6 kV cm−1, ε = 1817).