Porous ferroelectrics for energy harvesting applications

This paper provides an overview of energy harvesting using ferroelectric materials, with a particular focus on the energy harvesting capabilities of porous ferroelectric ceramics for both piezo- and pyroelectric harvesting. The benefits of introducing porosity into ferro- electrics such as lead zirconate titanate (PZT) has been known for over 30 years, but the potential advantages for energy harvesting from both ambient vibrations and temperature fluctuations have not been studied in depth. The article briefly discusses piezoelectric and pyro- electric energy harvesting, before evaluating the potential benefits of porous materials for increasing energy harvesting figures of merits and electromechanical/electrothermal coupling factors. Established processing routes are evaluated in terms of the final porous structure and the resulting effects on the electrical, thermal and mechanical properties

Chain orientation and defects in lamellar single crystals of syndiotactic polypropylene fractions

Sectorization is frequently observed in elongated rectangular single crystals of syndiotactic polypropylene (s-PP) grown from the melt in thin films. The crystals are bound laterally by {100} and {010} growth planes. The constituent sectors are readily observed because of a difference in thicknesses; specifically, the sectors bound by the {100} planes [the (100) growth sectors] are thicker than those bounded by the {010} planes [the (010) growth sectors]. Dark field (DF) transmission electron microscopy (TEM) was utilized to examine the chain orientation and lattice defects in the different growth sectors of s-PP single crystals. The (020) DF images exhibited pairs of bright streaks that are more or less perpendicular to the (100) planes and cross over the whole width of the (100) sectors. In the (200) DF images, the (100) sectors also exhibited similar but dimmer streaks than those in the (020) DF images. This suggests that the crystal c-axis orientation in the (100) crystal sectors undergoes a periodic change in inclination along both the longitudinal (parallel to the b-axis) and the transverse axis (parallel to the a-axis) directions of the single crystal. The ripples in the (100) sectors, previously observed in TEM, were also seen with atomic force microscopy as sinusoidal-like periodic height changes along the longitudinal axis direction at both room temperature and high temperatures. This periodic height change accounted for the pairs of bright streaks in the (020) DF images. The ripple formation was explained by lamellar thickening in the (010) sectors during crystal growth. This thickening process causes lateral contractions, which accumulate mainly along the longitudinal axis direction of the single crystal. On the other hand, the (020) DF images exhibited a relatively uniform brightness in the (010) sectors, while in the (200) DF images, several dark zones in the (010) sectors were more or less along the diagonal directions of the single crystal. This observation indicates that the crystal c-axis in these zones is slightly deviated from the (200) planarity due possibly to the lateral contraction in the (010) sectors. A regular Moiré pattern in the (010) sectors was observed in the (020) DF images, and no Moiré patterns were found in the (100) sectors. Again, this was presumably due to sinusoidal-like ripples, which substantially affect the crystal plane orientation with respect to the lamellar crystal normal. In the (200) DF images, only random Moiré fringes could be found and, in particular, when the (010) and the (100) sectors overlapped. However, regular Moiré fringes were observed continuously over both sectors in (220) DF images