Porous and Composite Materials Based on Lead-Free Ferroelectric Ceramics for Ultrasonic Transducers Applications

Microstructure evolution and electromechanical properties of (K,Na) NbO3‐based thick films

“…According to the f a and V L in each sample, a wavelength λ was calculated ( λ = V L / f a ), which decreased with the sintering temperature (typically 60 μm for 1090‐O and 46 μm for 1110‐O). With the same increase in the temperature from 1090°C to 1110°C, the mean pore area (see S5) increased and came closer to the value of the calculated wavelength: the scattering of the ultrasound waves by the pores led to an increase in the acoustic attenuation 42 and mechanical losses of the thick films. Roncari et al 43 observed a similar trend in porous piezoelectric ceramics: a narrow particle size distribution with smaller pores led to lower mechanical losses compared to a broad pore size distribution and/or a pore size distribution with larger pores.…”

Microstructure analysis of porous lead zirconate–titanate films

“…5,7,[20][21][22] Increasing film thickness due to mechanical stress relaxation in porous film is important for piezoelectric microelectromechanical systems (MEMS) applications because the output signal is increased by increasing the film thickness and the electromechanical response is enhanced by local elastic relaxations, 12,[23][24][25] decreasing permittivity can provide a better figure of merit for pyroelectric detectors, 16,26 the self-assembly of nanodots arrays can be used in memory technology, 17,18 porous ferroelectric films can be used to create gas sensors, [27][28][29] and different composite structures in which a porous ferroelectric material is filled with another material. [30][31][32][33] Porous structures in ferroelectric films can be achieved using sol-gel techniques. 10,11,13,14,18,34 Organic compounds known as porogens are added to a precursor solution and are subsequently incorporated into the growing metal-oxide-metal network during film formation as a result of phase segregation.…”

“…29,30 The physics of resin under pressure is similar to the seepage pr lar approaches have been used also to mod into a mold containing fiber mats. 23,[31][32][33][34][35][36][37][38] T in these cases to determine the resin flow ing times corresponding to different infilt Preceramic polycarbosilane polymers as precursors to make ceramic fibers 10,3 trix. [7][8][9]40,41 The chemical and volume ch pany ceramization of the polymer during documented in several studies.…”

“…Recently, films of porous ferroelectric ceramics have attracted increasing attention for various reasons, such as their ability to be prepared as thick films without cracking because of mechanical stress relaxation, 10–12 the tunability of their microstructure and ferroelectric properties, 13–16 their ability to be prepared as nanostructured objects via a self‐assembly process, 17–19 and their usefulness in the study of fundamental physical phenomena in ferroelectrics with defects 5,7,20–22 . Increasing film thickness due to mechanical stress relaxation in porous film is important for piezoelectric microelectromechanical systems (MEMS) applications because the output signal is increased by increasing the film thickness and the electromechanical response is enhanced by local elastic relaxations, 12,23–25 decreasing permittivity can provide a better figure of merit for pyroelectric detectors, 16,26 the self‐assembly of nanodots arrays can be used in memory technology, 17,18 porous ferroelectric films can be used to create gas sensors, 27–29 and different composite structures in which a porous ferroelectric material is filled with another material 30–33 …”

“…29,30 The physics of resin flow into a mold under pressure is similar to the seepage problem and so similar approaches have been used also to model the flow of resin into a mold containing fiber mats. 23,[31][32][33][34][35][36][37][38] The models are used in these cases to determine the resin flow front and mold filling times corresponding to different infiltration conditions.…”