Piezoelectric and structural properties of bismuth sodium potassium titanate lead-free ceramics for energy harvesting

The development of bulk piezoelectric ceramics with high energy conversion efficiency is of decisive importance for the requirements of the advanced energy harvesting devices toward miniaturization and integration. There is an additional motivation in the piezoelectric ceramics, lead titanate-zirconate (PZT) ceramics are the most widely used energy harvesting (EH) materials. This fact is important because legal restrictions on the use of lead in electronic devices have led to greater efforts being made to develop lead-free alternatives to PZT-based materials. Here, we propose the Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) lead-free piezoceramics as a good candidate for the replacement of toxic lead compounds for energy harvesting applications. For that, we have carried out a systematic study of the voltage generation of BNKT-based piezoceramics for (EH) purposes. Specifically, our results reveal that the BNKT–based lead-free piezoceramics show adequated effective capacitance and output energy due to more effective performance with a piezoelectric charge coefficient and a maximum generated output voltage as high as 12.8 pC/N and 19.9 V, respectively. Finally, we consider that the design of new lead-free piezoceramics with superior property coefficients and functionalities, such as the BNKT-based piezoceramics, should be seriously considered as candidates for the replacement of the current toxic lead-based compounds.

Gel Synthesis of Hexaferrites Pb1−xLaxFe12−xZnxO19 and Properties of Multiferroic Composite Ceramics PZT–Pb1−xLaxFe12−xZnxO19

We investigated the opportunities for obtaining hexaferrites Pb1−xLaxFe12−xZnxO19 (x = 0–1) from citrate–glycerin gel and showed that synthesis occurs via the formation of the Fe3O4 phase; products with a small amount of hematite impurity Fe2O3 can be obtained after firing at 800 to 900 °C with 0 ≤ x ≤ 0.5. If x > 0.5, perovskite-like LaFeO3 is formed in samples, so that if x = 0.9–1, the synthesis products virtually do not contain phases with hexaferrite structures and represent a mixture of LaFeO3, Fe2O3, and Fe3O4. Within the range of 0 ≤ x ≤ 0.5, the electrical and magnetic characteristics of hexaferrites Pb1−xLaxFe12−xZnxO19 are slightly dependent on x and have the following average values: A relative permittivity ε/ε0 ~ 45, a dielectric loss tangent tan δ ~ 0.6, an electrical resistivity R ~ 109 Ohm cm, coercivity Hc ~ 3 kOe, saturation magnetization Ms ~ 50 emu/g, and remanent magnetization Mr ~ 25 emu/g. The magnetoelectric (ME) ceramics 50 wt.% PZTNB-1 + 50 wt.% Pb1−xLaxFe12−xZnxO19 (PZTNB-1 is an industrial piezoelectric material based on lead titanate zirconate (PZT) do not contain impurity phases and have the following characteristics: Piezoelectric coefficients d33 = 10–60 and −d31 = 2–30 pC/N, piezoelectric voltage coefficients g33 = 2–13 and −g31 = 1–5 mV m/N, an electromechanical coupling coefficient Kp = 0.03–0.13, magnetic parameters Hc = 3–1 kOe, Ms = 50–30, and Mr = 25–12 emu/g. The maximum ME coupling coefficient ΔE/ΔH ~ 1.75 mV/(cm Oe) was achieved with x = 0.5.

A Large Piezoelectric Strain Recorded in BCT Ceramics Obtained by a Modified Pechini Method

There is a strong need in the industry to develop lead-free piezoelectrics for sensors and actuators. Although these materials have become an important component of many electronic devices, it is very important for the industry to decarbonise ceramic technology, especially through the introduction of modern sintering technologies. Among the many piezoelectric compounds available, Calcium Barium Titanate (BCT) have been widely investigated because of its similar performance to lead-containing Lead Titanate Zirconate (PZT). In this paper, a modified Pechini method for obtaining ceramic Ba0.9Ca0.1TiO3 nano-powders is described. Deviation from the established procedure resulted in the precipitation of the solution or obtaining of a low-quality (poorly crystallized) product with numerous impurities. The samples of BCT materials were examined to find their ideal microstructures and structures; these factors were confirmed by their outstanding X-ray diffraction spectra and high piezoelectric constant values that are comparable to commercial lead-containing materials.

Rare earth-doped lead titanate zirconate grown on carbon fibers by microwave-assisted hydrothermal synthesis

This study aimed to develop a flexible carbon fiber/oxide layer coating composite with improved electrical properties for use in electronic devices. For this, lead titanate zirconate, cerium-doped lead titanate zirconate, and yttrium-doped lead titanate zirconate were grown on carbon fibers via microwaves-assisted hydrothermal synthesis. The performed synthesis presented advantages when compared to conventional routes used in nanoparticles obtention since it allows the morphological control even at low temperatures. Carbon fiber was selected as substrates due to their thermal stability, excellent mechanical properties, chemical characteristics that allow the creation of functional groups on their surface, and good microwave radiation absorption. The composites were investigated by X-ray diffraction, spectroscopy Raman, and field emission scanning electron microscopy. The electrochemical evaluations were made by four-point probe method, cyclic voltammetry, and electrochemical impedance spectroscopy. The syntheses were successful and the carbon fiber coated with lead zirconate titanate had promissory results, with a boost in the electrical conductivity and better capacitance behavior when compared to the undoped carbon fiber, showing to be a good alternative for applications in electrical devices.