Novel lead-free BCZT-based ceramic with thermally-stable recovered energy density and increased energy storage efficiency

The eco-responsible lead-free piezoelectric ceramics have been intensively searched for more than a decade, however, the final goal to replace toxic ceramics like lead zirconate titanate (PZT) with lead-free compounds, having comparable or even better performance has not yet been reached. In this road, the lead-free ceramics Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT), possessing excellent dielectric, ferroelectric, and piezoelectric properties are regarded as serious candidates for the PZT replacement. Besides, nanostructuring BCZT is of paramount importance to enhance these functionalities even more. Here, BCZT multipodes are designed by template-growth hydrothermal synthesis using hydrogen zirconate titanate nanowires. We demonstrate that the fabricated BCZT multipodes exhibit high dielectric permittivity of 5300 with a temperature stability coefficient of ±5.9% between 20 and 140 °C. A significant recovered energy density of 315.0 mJ/cm3 with high thermal stability and high energy storage efficiency of 87.4%, and enhanced large-signal piezoelectric coefficient (310 pm/V) are found. Compared to the traditional BCZT ceramics reported in the literature, relying on high-temperature processing, our sample exhibits boosted energy storage parameters at a much lower temperature. These outcomes may offer a new strategy to tailor eco-responsible relaxor ferroelectrics toward superior energy storage performance for ceramic capacitor applications

The benefits of combining 1D and 3D nanofillers in a piezocomposite nanogenerator for biomechanical energy harvesting

Mechanical energy harvesting using piezoelectric nanogenerators (PNGs) offers an attractive solution for driving low-power portable devices and self-powered electronic systems. Here, we designed an eco-friendly and flexible piezocomposite nanogenerator (c-PNG) based on H-2(Zr0.1Ti0.9)(3)O-7 nanowires (HZTO-nw) and Ba0.85Ca0.15Zr0.10Ti0.90O3 multipods (BCZT-mp) as fillers and polylactic acid (PLA) as a biodegradable polymer matrix. The effects of the applied stress amplitude, frequency and pressing duration on the electric outputs in the piezocomposite nanogenerator (c-PNG) device were investigated by simultaneous recording of the mechanical input and the electrical outputs. The fabricated c-PNG shows a maximum output voltage, current and volumetric power density of 11.5 V, 0.6 mu A and 9.2 mW cm(-3), respectively, under cyclic finger imparting. A high-pressure sensitivity of 0.86 V kPa(-1) (equivalent to 3.6 V N-1) and fast response time of 45 ms were obtained in the dynamic pressure sensing. Besides this, the c-PNG demonstrates high-stability and durability of the electrical outputs for around three months, and can drive commercial electronics (charging capacitor, glowing light-emitting diodes and powering a calculator). Multi-physics simulations indicate that the presence of BCZT-mp is crucial in enhancing the piezoelectric response of the c-PNG. Accordingly, this work reveals that combining 1D and 3D fillers in a polymer composite-based PNG could be beneficial in improving the mechanical energy harvesting performances in flexible piezoelectric nanogenerators for application in electronic skin and wearable devices

Enhanced dielectric and electrocaloric properties in lead-free rod-like BCZT ceramics

Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) lead-free ceramics demonstrated excellent dielectric, ferroelectric, and piezoelectric properties at the morphotropic phase boundary (MPB). So far, to study the effect of morphological changes on dielectric and ferroelectric properties in lead-free BCZT ceramics, researchers have mostly focused on the influence of spherical grain shape change. In this study, BCZT ceramics with rod-like grains and aspect ratio of about 10 were synthesized by surfactant-assisted solvothermal route. X-ray diffraction (XRD) and selected area electron diffraction (SAED) performed at room temperature confirm the crystallization of pure perovskite with tetragonal symmetry. Scanning electron microscopy (SEM) image showed that BCZT ceramics have kept the 1D rod-like grains with an average aspect ratio of about 4. Rod-like BCZT ceramics exhibit enhanced dielectric ferroelectric (ɛr = 11,906, tanδ = 0.014, Pr = 6.01 μgC/cm2, and Ec = 2.46 kV/cm), and electrocaloric properties (ΔT = 0.492 K and gZ = 0.289 (K·mm)/kV at 17 kV/cm) with respect to spherical BCZT ceramics. Therefore, rod-like BCZT lead-free ceramics have good potential to be used in solid-state refrigeration technology

Morphogenesis mechanisms in the hydrothermal growth of lead-free BCZT nanostructured multipods

Due to growing environmental concerns about the toxicity of lead-based piezoelectrics, the replacement of Pb-based materials with homologs with comparable piezoelectric properties but without lead is an emergent task. Since 2009, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) materials have aroused considerable attention as a replacement due to their excellent dielectric, ferroelectric and piezoelectric properties. Nanostructuring of BCZT can enhance these functionalities even more. Here, templated-growth of BCZT nanostructured multipods with hydrogen zirconate titanate nanowires (HZTO-NWs) was investigated under hydrothermal conditions. The effects of the precursor's concentrations and the hydrothermal reaction time on the morphological formation of BCZT nanostructures were investigated. Besides, composition, structure and phase analysis studies were carried out, and the growth mechanism of BCZT multipods was proposed. It was found that the precursor's concentrations and dwell time in hydrothermal reactions play a critical role in the formation of BCZT multipods, and the desirable BCZT phase was obtained in samples using low barium and calcium concentrations and at a short reaction time. This research has general validity and can be extended to design more complex perovskite oxides

A flexible self-poled piezocomposite nanogenerator based on H₂(Zr_0.1Ti_0.9)₃O₇ nanowires and polylactic acid biopolymer

The field of piezoelectric nanogenerators is rapidly growing as a promising technology for driving lowpower portable devices and self-powered electronic systems by converting wasted mechanical energy into electric energy. In this study, we designed a flexible and self-poled piezocomposite nanogenerator based on lead-free H 2 (Zr 0.1 Ti 0.9) 3 O 7 (HZTO) nanowires and a polylactic acid (PLA) biodegradable polymer. By using a piezoresponse force microscope (PFM), the piezoelectric coefficient (d 33) of a single HZTO nanowire was found to be 26 pm V À1. The piezoelectric energy harvesting performances of a selfpoled piezocomposite film fabricated by embedding core-shell structured HZTO nanowires by polydopamine into the PLA matrix were tested. The piezoelectric nanogenerator demonstrated enhanced output performances (an open-circuit voltage of 5.41 V, short-circuit current of 0.26 mA and maximum power density of 463.5 mW cm À3 at a low resistive load of 2.5 MU). Besides, the developed device can charge different capacitors by regular mechanical impartations and can power a red lightemitting LED diode by various biomechanical motions. This study reveals the benefits of combining HZTO nanowires and PLA biopolymer in designing high-performance piezoelectric nanocomposites for biomechanical energy harvesting

Enhanced electrical properties and large electrocaloric effect in lead-free Ba0.8Ca0.2ZrxTi1−xO3 (x = 0 and 0.02) ceramics

The effects of 2% Zr introduction in Ba0.8Ca0.2TiO3 (BCT) system on its electrical and electrocaloric properties was investigated. BCT and Ba0.8Ca0.2Zr0.02Ti0.98O3 (BCZT) ceramics synthesized by solid-state processing were crystallized in a pure perovskite phase with a group space P4mm. After Zr insertion, the enhanced dielectric constant was obtained around the Curie temperature (Tc) in BCZT ceramic (εr = 6330 at Tc = 388 K) compared to BCT ceramic (εr = 5080 at Tc = 388.6 K). Moreover, the large-signal piezoelectric coefficient (d∗33) was improved from 270 to 310 pm/V in BCT and BCZT ceramics, respectively, under a moderate electric field of 25 kV/cm. The electrocaloric effect was determined via indirect and direct methods. In the indirect approach, the electrocaloric temperature change (ΔT) was calculated via Maxwell relation, and the measured ferroelectric polarization P (E, T) extracted from the P–E curves recorded at 24 kV/cm. The maximum values of ΔT = 0.68 K and the electrocaloric responsivity ζ = 0.283 K mm/kV obtained at 385 K in BCZT ceramic were found to be higher than those observed in BCT ceramic (ΔT = 0.37 K and ζ = 0.154 K mm/kV at 387 K). In the direct approach, ΔT was measured utilizing a modified high-resolution calorimeter at 14 kV/cm. As the direct method is more sensitive to the latent heat, it provided larger values for smaller applied field, i.e., ΔT = 0.474 and 0.668 K for BCT and BCZT ceramics, respectively. A significant ζ of 0.477 K mm/kV was obtained in BCZT at 385 K and 14 kV/cm that matches the values found in lead-based materials. These results suggest that BCZT lead-free ceramics could have an excellent potential to be used in solid-state refrigeration applications