RESUMEN
The design of lead-free ceramics for piezoelectric energy harvesting applications has become a hot topic. Among these materials, Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) and BaTi0.89Sn0.11O3 (BTSn) are considered as potential candidates due to their enhanced piezoelectric properties. Here, the structural, electrical, piezoelectric and piezoelectric energy harvesting properties of the (1 - x)Ba0.85Ca0.15Zr0.10Ti0.90O3-xBaTi0.89Sn0.11O3 (xBTSn, x = 0.2, 0.4 and 0.6) system are investigated. A systematic study of the structural properties of the xBTSn samples was carried out using X-ray diffraction, Raman spectroscopy, and dielectric measurements. The addition of BTSn allows a successive phase transition, which broadens the application temperature range. The enhanced piezoelectric energy harvesting properties were found in the 0.2BTSn ceramic, where the large-signal and small-signal piezoelectric coefficients, piezoelectric voltage and the piezoelectric figure of merit reached 245 pm V-1, 228 pC N-1, 16.2 mV m N-1 and 3.7 pm2 N-1, respectively. Consequently, the combination of BCZT and BTSn could provide suitable lead-free materials with enhanced piezoelectric energy harvesting performances.
RESUMEN
Ferroelectric domain walls provide a fertile environment for novel materials physics. If a polarization discontinuity arises, it can drive a redistribution of electronic carriers and changes in band structure, which often result in emergent 2D conductivity. If such a discontinuity is not tolerated, then its amelioration usually involves the formation of complex topological patterns, such as flux-closure domains, dipolar vortices, skyrmions, merons, or Hopfions. The degrees of freedom required for the development of such patterns, in which dipolar rotation is a hallmark, are readily found in multiaxial ferroelectrics. In uniaxial ferroelectrics, where only two opposite polar orientations are possible, it has been assumed that discontinuities are unavoidable when antiparallel components of polarization meet. This perception has been borne out by the appearance of charged conducting domain walls in systems such as hexagonal manganites and lithium niobate. Here, experimental and theoretical investigations on lead germanate (Pb5 Ge3 O11 ) reveal that polar discontinuities can be obviated at head-to-head and tail-to-tail domain walls by mutual domain bifurcation along two different axes, creating a characteristic saddle-point domain wall morphology and associated novel dipolar topology, removing the need for screening charge accumulation and associated conductivity enhancement.
RESUMEN
It is well known that the ferroelectric layers in dielectric/ferroelectric/dielectric heterostructures harbor polarization domains resulting in the negative capacitance crucial for manufacturing energy-efficient field-effect transistors. However, the temperature behavior of the characteristic dielectric properties, and, hence, the corresponding behavior of the negative capacitance, are still poorly understood, restraining the technological progress thereof. Here we investigate the temperature-dependent properties of domain structures in the SrTiO3/PbTiO3/SrTiO3 heterostructures and demonstrate that the temperature-thickness phase diagram of the system includes the ferroelectric and paraelectric regions, which exhibit different responses to the applied electric field. Using phase-field modeling and analytical calculations we find the temperature dependence of the dielectric constant of ferroelectric layers and identify the regions of the phase diagram wherein the system demonstrates negative capacitance. We further discuss the optimal routes for implementing negative capacitance in energy-efficient ferroelectric field-effect transistors.
RESUMEN
The lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) relaxor ferroelectric ceramic has aroused much attention due to its enhanced piezoelectric, energy storage and electrocaloric properties. In this study, the BCZT ceramic was elaborated by the solid-state reaction route, and the temperature-dependence of the structural, electrical, piezoelectric, energy storage and electrocaloric properties was investigated. X-ray diffraction analysis revealed a pure perovskite phase, and the temperature-dependence of Raman spectroscopy, dielectric and ferroelectric measurements revealed the phase transitions in the BCZT ceramic. At room temperature, the strain and the large-signal piezoelectric coefficient reached a maximum of 0.062% and 234 pm V-1, respectively. Furthermore, enhanced recovered energy density (W rec = 62 mJ cm-3) and high-energy storage efficiency (η) of 72.9% at 130 °C were found. The BCZT ceramic demonstrated excellent thermal stability of the energy storage variation (ESV), less than ±5.5% in the temperature range of 30-100 °C compared to other lead-free ceramics. The electrocaloric response in the BCZT ceramic was explored via the indirect approach by using the Maxwell relation. Significant electrocaloric temperature change (ΔT) of 0.57 K over a broad temperature span (T span = 70 °C) and enhanced coefficient of performance (COP = 11) were obtained under 25 kV cm-1. The obtained results make the BCZT ceramic a suitable eco-friendly material for energy storage and solid-state electrocaloric cooling devices.
RESUMEN
The possibility of the development of MEMS devices based on the tunable ferroelectric film Ba 0.8Sr 0.2O3 properties under uniaxial deformation was studied theoretically. The thermodynamic model of the phase transitions for the film under uniaxial stress was constructed. The behavior of the material constants for the film in various phase states was investigated. The propagation properties of the surface acoustic wave (SAW) under the uniaxial stress were studied for the film located on the single-crystal silicon substrate. It was shown that the SAW resonance frequency changes within 3 MHz for the frequency of 274 MHz, and 9 MHz for the frequency of 512 MHz.