5 research outputs found
Absence of Morphotropic Phase Boundary Effects in BiFeO3-PbTiO3 Thin Films Grown via a Chemical Multilayer Deposition Method
Here, we report the unusual behaviour shown by the (BiFeO3)1-x-(PbTiO3)x
(BF-xPT) films prepared using a multilayer deposition approach by chemical
solution deposition method. Thin film samples of various compositions were
prepared by depositing several bilayers of BF and PT precursors by varying the
BF or PT layer thicknesses. X-ray diffraction showed that final samples of all
compositions show mixing of the two compounds resulting in a single phase
mixture, also confirmed by transmission electron microscopy. In contrast to
bulk equilibrium compositions, our samples show a monoclinic (MA type)
structure suggesting disappearance of morphotropic phase boundary (MPB) about x
= 0.30 as observed in the bulk. This is accompanied by the lack of any
enhancement of remnant polarization at MPB as shown by the ferroelectric
measurements. Magnetic measurements show that the magnetization of the samples
increases with increasing BF content. Significant magnetization of the samples
indicates melting of spin spirals in the BF-xPT arising from random
distribution of iron atoms across the film. Absence of Fe2+ ions in the films
was corroborated by X-ray photoelectron spectroscopy measurements. The results
illustrate that used thin film processing methodology significantly changes the
structural evolution in contrast to predictions from the equilibrium phase
diagram as well as modify the functional characteristics of BP-xPT system
dramatically.Comment: 15 pages, 6 figure
Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions
Solid solutions of (1-x)LaFeO3-(x)PbTiO3 (0<x<1) have been prepared by
conventional solid-state reaction. These complex perovskites have been studied
by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented
with dielectric, magnetic, heat capacity and M\"ossbauer measurements. Complete
solubility in the perovskite series was demonstrated. The NPD and XRPD patterns
were successfully refined as orthorhombic (x \leq 0.7) and tetragonal (x \geq
0.8). A composition-driven phase transformation occurs within the interval
0.7<x<0.8. The samples with x<0.5 showed evidence of long-range magnetic
ordering with an G-type antiferromagnetic arrangement of the magnetic moments
of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on
the obtained experimental data, a combined structural and magnetic phase
diagram has been constructed. The factors governing the structural, dielectric
and magnetic properties of (1-x) LaFeO3 - (x)PbTiO3 solid solutions are
discussed, as well as their possible multiferroicity.Comment: 33 pages, 15 figure
Structure and electrical properties of ternary BiFeO3-BaTiO3-PbTiO3 high-temperature piezoceramics
Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web
The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño–Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts