Enhancing Solution-Derived Piezoelectric Modified BaTiO₃ Films Through In-Situ Microstructural Characterization

Today, piezoelectric materials play an important role in numerous applications such as sensors, actuators, transducers, and energy harvesters. Piezoelectric energy harvesters cannot reach the efficiency and scale of solar cells or wind turbines, but they are excellent power sources where electrical cables are undesired and miniaturization is a key factor. Lead-based piezoelectric materials such as Pb(Zr,Ti)O₃ (PZT) are currently the most widely used material in such systems. This is due to their strong piezoelectric coefficient and electromechanical coupling coefficient. However, the use of PZT is not an option due to the presence of lead, and the development of alternative "greener" and "superior" materials with comparable or better piezoelectric properties is required. Barium titanate (BaTiO₃) is one of the suitable lead-free piezoelectric candidates due to its promising piezoelectric properties. To improve its piezoelectric properties, several BaTiO₃-based solid solutions with different substituents have been studied. In 2009, some researchers have reported a significant breakthrough in BaTiO₃ perovskite doped with Ca and Zr atoms, leading to the (Ba,Ca)(Ti,Zr)O₃ (BXT) solid solution with an outstanding piezoelectric coefficient.<br/><br/>Since BXT material offers promising piezoelectric properties, making thin films of this material is of particular interest for use in various applications. Also, the integration of piezoelectric films on silicon (Si) or silicon nitride (SiN) based platforms is crucial for the miniaturization of electronic and photonic components. In this work, chemical solution deposition (CSD) technique is introduced as a rapid integration to develop a cost-effective, reproducible and high-quality industrial pathway to piezoelectric BXT film on desired substrate. Therefore, the formulation of the environmentally friendly BXT precursor solution is highly important and must be stable prior to the CSD process with good wetting behavior and good homogeneity on desired substrate. Here we are able to develop the environmentally benign BXT inks based on the short carboxylic acid route as metal organic decomposition (MOD) method. It results in BXT material with promising piezoelectric properties, but has a Curie temperature of 85 °C and thus shows a poor piezoelectric thermal stability upon heating, which deeply limits its practical application.<br/><br/>Therefore, in this work, several compositional and microstructural modifications via the combination of CSD and pulsed laser deposition (PLD) techniques are introduced (and with the support of computational screening) to enhance temperature stability and the piezoelectric response of BXT films. These films are investigated via electrical and microstructural measurements (both in-situ and ex-situ) to understand the modification of BXT film. Here, in-situ high temperature conventional x-ray diffraction (XRD) measurements will be carried out to understand the temperature-dependent microstructural evolution (nucleation and growth mechanism during the thermal processing) in these modified BXT films. This approach present some new specific challenges to improve the properties of BXT films for the successful implementation of piezoelectric lead-free material in several applications.