Effect of Hydrothermal Treatment and Doping on the Microstructural Features of Sol-Gel Derived BaTiO3 Nanoparticles.

Nico Zamperlin,Alessandro Pegoretti,Riccardo Ceccato,Sandra Dirè,Marco Fontana,Andrea Chiappini

doi:10.3390/ma14154345

Abstract

Barium Titanate (BaTiO3) is one of the most promising lead-free ferroelectric materials for the development of piezoelectric nanocomposites for nanogenerators and sensors. The miniaturization of electronic devices is pushing researchers to produce nanometric-sized particles to be embedded into flexible polymeric matrices. Here, we present the sol-gel preparation of crystalline BaTiO3 nanoparticles (NPs) obtained by reacting barium acetate (Ba(CH3COO)2) and titanium (IV) isopropoxide (Ti(OiPr)4). The reaction was performed both at ambient conditions and by a hydrothermal process carried on at 200 °C for times ranging from 2 to 8 h. Doped BaTiO3 nanoparticles were also produced by addition of Na, Ca, and Bi cations. The powders were annealed at 900 °C in order to improve NPs crystallinity and promote the cubic-to-tetragonal (c⟶t) phase transformation. The microstructural features of nanoparticles were investigated in dependence of both the hydrothermal reaction time and the presence of dopants. It is found that short hydrothermal treatment (2 h) can produce BaTiO3 spherical and more homogeneous nanoparticles with respect to longer hydrothermal treatments (4 h, 6 h, 8 h). These particles (2 h) are characterized by decreased dimension (approx. 120 nm), narrower size distribution and higher tetragonality (1.007) in comparison with particles prepared at ambient pressure (1.003). In addition, the short hydrothermal treatment (2 h) produces particles with tetragonality comparable to the one obtained after the longest process (8 h). Finally, dopants were found to affect to different extents both the c⟶t phase transformation and the crystallite sizes.

Highlights

During the last few years, there has been an increasing interest in the development of piezoelectric composite materials for energy harvesting, actuators, and soft sensors applications
Preliminary experiments have been done in order to optimize the sol−gel synthesis paparameters, in particular the molar ratio between Ti and Ba precursors (Ba/Ti ratio)
Furtherit was demonstrated that a longer duration of the hydrothermal process causes a broadmore, it was demonstrated that a longer duration of the hydrothermal process causes a ening in particle size distribution combined with the appearance of some necks among broadening in particle size distribution combined with the appearance of some necks particles

Summary

Introduction

During the last few years, there has been an increasing interest in the development of piezoelectric composite materials for energy harvesting, actuators, and soft sensors applications. The coupling of piezo-ceramic fillers with polymeric matrices, such as polydimethylsiloxane (PDMS) and polyvinylidenefluoride (PVDF), can combine high dielectric and piezoelectric properties of ceramics with flexibility and softness of polymers [1,2,3]. There are several issues concerning this material due to the presence of lead (Pb) Pb is harmful both for the environment and human health; additional problems are related to its correct disposal. In this scenario, in the last few years, researchers have been pushing on to find a valid, high performance, lead-free alternative to PZT [8,9]. The most widely studied Pb-free piezoelectric ceramics are titanates (in particular barium-strontium titanate (Ba1−x Srx TiO3 )

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