Coupon specimens of poled and depoled lead zirconate titanate (PZT) are examined under combined stress wave and electric loading conditions. Mode‐I crack initiation and fracture behavior is examined using ultrahigh‐speed imaging and two‐dimensional digital image correlation. The dynamic critical stress intensity factor (
Ferroelectric films suffer from both aging and degradation under high ac‐field drive conditions due to loss of polarization with time. In this study, the roles of defect chemistry and internal electric fields on the long‐term stability of the properties of piezoelectric films were explored. For this purpose, lead zirconate titanate (PZT) films with a Zr/Ti ratio of 52/48 doped with Mn‐ (PMZT) or Nb‐ (PNZT) were deposited on Pt coated Si substrates by the sol‐gel method. It was demonstrated that the magnitude of the internal field is much higher in PMZT films compared to PNZT films after poling in the temperature range of 25‐200°C under an electric field of −240 kV/cm. The development of the internal field is thermally activated, with activation energies from 0.5 ± 0.06 to 0.8 ± 0.1 eV in Mn doped films and from 0.8 ± 0.1 to 1.2 ± 0.2 eV in Nb doped films. The different activation energies for imprint suggests that the physical mechanism underlying the evolution of the internal field in PMZT and PNZT films differs; the enhanced internal field upon poling is attributed to (a) alignment of oxygen vacancy—acceptor ion defect dipoles (
- PAR ID:
- 10459897
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 102
- Issue:
- 9
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 5328-5341
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract ) is extracted using measured displacement fields ahead of the impulsively loaded crack tip, and compared between poled and depoled plates that were either under no electric field, positive 0.46 kV/mm electric field, or negative 0.46 kV/mm electric field. Poled specimens had a poling direction and applied electric field direction normal to the crack front. The addition of an electric field resulted in a crack‐enhancing effect, where the dynamic fracture toughness of poled specimens under 0.46 kV/mm was almost half that of samples with no electric field. Depoled samples experienced almost no change in dynamic fracture toughness with the addition of an electric field. -
more » « less
Abstract We report the pulsed‐laser deposition of epitaxial double‐perovskite Bi2FeCrO6(BFCO) films on the (001)‐, (110), and (111)‐oriented single‐crystal SrTiO3substrates. All of the BFCO films with various orientations show the
and superlattice‐diffraction peaks. The intensity ratios between the ‐superlattice and the main 111‐diffraction peak can be tailored by simply adjusting the laser repetition rate and substrate temperature, reaching up to 4.4%. However, both optical absorption spectra and magnetic measurements evidence that the strong superlattice peaks are not correlated with the B ‐site Fe3+/Cr3+cation ordering. Instead, the epitaxial (111)‐oriented Bi2FeCrO6films show an enhanced remanent polarization of 92 μC/cm2at 10 K, much larger than the predicted values by density‐functional theory calculations. Positive‐up‐negative‐down (PUND) measurements with a time interval of 10 μs further support these observations. Therefore, our experimental results reveal that the strong superlattice peaks may come fromA ‐ orB ‐site cation shifts along the pseudo‐cubic [111] direction, which further enhance the ferroelectric polarization of the BFCO thin films. -
more » « less
Abstract The hydration of the two most reactive phases of ordinary Portland cement (OPC), tricalcium silicate (C3S), and tricalcium aluminate (C3A) is successfully halted when the activity of water (
) falls below critical thresholds of 0.70 and 0.45, respectively. It has been established that the reduction in relative humidity (RH) and suppresses the hydration of all anhydrous phases in OPC, including less explored phases like dicalcium silicate, that is, belite (β‐C2S). However, the degree of suppression, that is, the critical threshold, for β‐C2S, standalone has yet to be established. This study utilizes isothermal microcalorimetry and X‐ray diffraction techniques to elucidate the influence of on the hydration of ‐C2S suspensions via incremental replacements of water with isopropanol (IPA). Experimentally, this study shows that with increasing IPA replacements, hydration is increasingly suppressed until eventually brought to a halt at a critical threshold of approximately 27.7% IPA on a weight basis (wt.%IPA). From thermodynamic estimations, the exact critical threshold and solubility product constant of ‐C2S ( ) are established as 0.913 and 10−12.68, respectively. This study enables enhanced understanding of β‐C2S reactivity and provides thermodynamic parameters during the hydration of β‐C2S‐containing cementitious systems such as OPC‐based and calcium aluminate‐based systems. -
more » « less
Abstract As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency
. We find that below the °C isotherm, is on average reduced by a scaling factor of , a 12% reduction, per decade that intensifies with depth. At °C, we observe the biggest change: , or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about , although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed. -
more » « less
Abstract While monazite (LaPO4) does not flash sinter even at high fields of 1130 V/cm and temperatures of 1450°C, composite systems of 8YSZ–LaPO4and Al2O3–LaPO4have been found to more readily flash sinter. 8YSZ added to LaPO4greatly lowered the furnace temperature for flash to 1100°C using a field of only 250 V/cm. In these experiments,
‐Al2O3alone also did not flash sinter at 1450°C even with high fields of 1130 V/cm, but composites of Al2O3–LaPO4powders flash sintered at 900‐1080 V/cm at 1450°C. Alumina–monazite (Al2O3–LaPO4) composites with compositions ranging from 25 vol% to 75 vol% Al2O3were flash sintered with current limits from 2 to 25 mA/mm2. Microstructures were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A eutectic microstructure was observed to form in all flash sintered Al2O3–LaPO4composites. With higher power (higher current limits), eutectic structures with regular lamellar regions were found to coexist in the channeled region (where both the current and the temperature were the highest) with large hexagonal‐shaped ‐Al2O3grains (up to 75 m) and large irregular LaPO4grains. With lower power (lower current limits), an irregular eutectic microstructure was dominant, and there was minimal abnormal grain growth. These results indicate that Al2O3–LaPO4is a eutectic‐forming system and the eutectic temperature was reached locally during flash sintering in regions. These eutectic microstructures with lamellar dimensions on the scale of 100 nm offer potential for improved mechanical properties.
