Investigation of structural phase transitions in ferroelectric BaTiO3 thin films from composite solutions

Abstract

In this study, we investigate the synthesis and structural phase evolution of barium titanate (BaTiO3) thin films produced using a polymer-assisted sol-gel method. This innovative approach integrates the advantages of polymer-based solutions with the sol-gel method. The unique viscoelastic properties of polyvinylpyrrolidone (PVP) enhance the development of homogenous BaTiO3 thin films with controlled microstructures. To optimize these properties, we formulated composite solutions by varying the concentrations of PVP in conjunction with the sol-gel precursor. The composite precursor solutions were deposited onto quartz substrates via the spin-coating technique and subsequently sintered at temperatures of 400, 500, 700, and 900°C to promote optimal BaTiO3 crystallization. Structural phase characterization was performed using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). TGA data indicated significant weight loss due to moisture evaporation occurring around 200°C, followed by PVP decomposition at approximately 430°C, with a flash point thermal event occurring at around 450°C. The monitoring of structural phase transitions throughout the sintering process revealed a transformation from an amorphous phase to crystalline barium carbonate (BaCO3), ultimately leading to the development of the ferroelectric BaTiO3 phase. The BaCO3 phase was identified at 400°C and gradually decomposed at 500, 700 and 900°C, while the BaTiO3 phase emerged at 700°C and achieved full consolidation above 900°C. The morphological evolution was monitored through scanning electron microscopy (SEM), and the chemical composition was analyzed using energy dispersive spectroscopy (EDS) for elemental mapping of Ba, Ti, C and O. Notably, films with higher concentrations of the polymer exhibited an increased content of BaCO3. The structural and electronic properties of the obtained phases during sintering were evaluated through photoluminescence (PL). This revealed defect-mediated emissions that intensified and exhibited a blue shift with increased sintering temperature. The findings of this research highlight the potential of the polymer-assisted sol-gel method as an effective route for synthesizing ferroelectric thin-film materials with controlled microstructures. This study provides valuable insights into the synthesis and characterization of ferroelectric materials and establishes a novel methodology for optimizing thin film properties that can be used in piezoelectric and microelectronic applications.