ABSTRACT
The atomic-level response of zigzag ferroelectric domain walls (DWs) was investigated with in situ bias scanning transmission electron microscopy (STEM) in a subcoercive-field regime. Atomic-level movement of a single DW was observed. Unexpectedly, the change in the position of the DW, determined from the atomic displacement, did not follow the position of the strain field when the electric field was applied. This can be explained as low mobility defect segregation at the initial DW position, such as ordered clusters of oxygen vacancies. Further, the triangular apex of the zigzag wall is pinned, but it changes its shape and becomes asymmetric under electrical stimuli. This phenomenon is accompanied by strain and bound charge redistribution. We report on unique atomic-scale phenomena at the DW level and show that in situ STEM studies with atomic resolution are very relevant as they complement, and sometimes challenge, the knowledge gained from lower resolution studies.
ABSTRACT
Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) relaxor ferroelectric ceramics exhibit enhanced energy storage and electrocaloric performances due to their excellent dielectric and ferroelectric properties. In this study, the temperature-dependence of the structural and dielectric properties, as well as the field and temperature-dependence of the energy storage and the electrocaloric properties in BCZT ceramics elaborated at low-temperature hydrothermal processing are investigated. X-ray diffraction and Raman spectroscopy results confirmed the ferroelectric-paraelectric phase transition in the BCZT ceramic. At room temperature and 1 kHz, the dielectric constant and dielectric loss reached 5000 and 0.029, respectively. The BCZT ceramic showed a large recovered energy density (W rec) of 414.1 mJ cm-3 at 380 K, with an energy efficiency of 78.6%, and high thermal-stability of W rec of 3.9% in the temperature range of 340-400 K. The electrocaloric effect in BCZT was explored via an indirect approach following the Maxwell relation at 60 kV cm-1. The significant electrocaloric temperature change of 1.479 K at 367 K, a broad temperature span of 87 K, an enhanced refrigerant capacity of 140.33 J kg-1, and a high coefficient of performance of 6.12 obtained at 60 kV cm-1 make BCZT ceramics potentially useful coolant materials in the development of future eco-friendly solid-state refrigeration technology.
ABSTRACT
Piezoelectric ceramic resonant pressure sensors have shown potential as sensing elements for harsh environments, such as elevated temperatures. For operating temperatures exceeding ~250 °C, conventional and widely used Pb(Zr,Ti)O3 (PZT) piezoelectrics should be replaced. Here, a ceramic pressure sensor from low-temperature co-fired ceramics (LTCC) was constructed by integrating a piezoelectric actuator made from bismuth ferrite (BiFeO3) on a diaphragm. This ferroelectric material was selected because of its high Curie temperature (TC = 825 °C) and as a lead-free piezoelectric extensively investigated for high-temperature applications. In order to construct a sensor with suitable pressure sensitivity, numerical simulations were used to define the optimum construction dimensions. The functionality of the pressure sensor was tested up to 201 °C. The measurements confirmed a pressure sensitivity, i.e., resonance frequency shift of the sensor per unit of pressure, of -8.7 Hz/kPa up to 171 °C. It was suggested that the main reason for the hindered operation at the elevated temperatures could lie in the thermo-mechanical properties of the diaphragm and the adhesive bonding at the actuator-diaphragm interconnection.
