Close-circuit domain quadruplets in BaTiO3_3 nanorods embedded in SrTiO3_3 film

Cylindrical BaTiO3 nanorods embedded in (100)-oriented SrTiO3 epitaxial film in a brush-like configuration are investigated in the framework of the Ginzburg-Landau-Devonshire model. It is shown that strain compatibility at BaTiO3/SrTiO3 interfaces keeps BaTiO3 nanorods in the rhombohedral phase even at room temperature. Depolarization field at the BaTiO3/SrTiO3 interfaces is reduced by an emission of the 109-degree or 71-degree domain boundaries. In case of nanorods of about 10-80 nm diameter, the ferroelectric domains are found to form a quadruplet with a robust flux-closure arrangement of the in-plane components of the spontaneous polarization. The out-of-plane components of the polarization are either balanced or oriented up or down along the nanorod axis. Switching of the out-of-plane polarization with coercive field of about $5.10^6$ V/m occurs as a collapse of a 71-degree cylindrical domain boundary formed at the curved circumference surface of the nanorod. The remnant domain quadruplet configuration is chiral, with the $C_4$ macroscopic symmetry. More complex stable domain configurations with coexisting clockwise and anticlockwise quadruplets contain interesting arrangement of strongly curved 71-degree boundaries.Comment: Erratta - corrected error in Fig.

Central mode and soft mode behavior in PbMg1/Nb2/3O3 relaxor ferroelectric

The relaxor ferroelectric PbMg1/Nb2/3O3 was investigated by means of broad-band dielectric and Fourier Transform Infrared (FTIR) transmission spectroscopy in the frequency range from 1 MHz to 15 THz at temperatures between 20 and 900 K using PMN films on infrared transparent sapphire substrates. While thin film relaxors display reduced dielectric permittivity at low frequencies, their high frequency intrinsic or lattice response is shown to be the same as single crystal/ceramic specemins. It was observed that in contrast to the results of inelastic neutron scattering, the optic soft mode was underdamped at all temperatures. On heating, the TO1 soft phonon followed the Cochran law with an extrapolated critical temperature equal to the Burns temperature of 670 K and softened down to 50 cm-1. Above 450 K the soft mode frequency leveled off and slightly increased above the Burns temperature. A central mode, describing the dynamics of polar nanoclusters appeared below the Burns temperature at frequencies near the optic soft mode and dramatically slowed down below 1 MHz on cooling below room temperature. It broadened on cooling, giving rise to frequency independent losses in microwave and lower frequency range below the freezing temperature of 200 K. In addition, a new heavily damped mode appeared in the FTIR spectra below the soft mode frequency at room temperature and below. The origin of this mode as well as the discrepancy between the soft mode damping in neutron and infrared spectra is discussed.Comment: 7 pages with 7 figures, submitted to Phys. Rev.

Issues and solutions for researching weed eradication target species

Species biology drives the frequency, duration and extent of survey and control activities in weed eradication programs. Researching the key biological characters can be difficult when plants occur at limited locations and are controlled immediately by field crews who are dedicated to preventing reproduction. Within the National Four Tropical Weeds Eradication Program and the former National Siam Weed Eradication Program, key information needed by the eradication teams has been obtained through a combination of field, glasshouse and laboratory studies without jeopardising the eradication objective. Information gained on seed longevity, age to reproductive maturity, dispersal and control options has been used to direct survey and control activities. Planned and opportunistic data collections will continue to provide biological information to refine eradication activities

Issues and solutions for researching weed eradication target species

Species biology drives the frequency, duration and extent of survey and control activities in weed eradication programs. Researching the key biological characters can be difficult when plants occur at limited locations and are controlled immediately by field crews who are dedicated to preventing reproduction. Within the National Four Tropical Weeds Eradication Program and the former National Siam Weed Eradication Program, key information needed by the eradication teams has been obtained through a combination of field, glasshouse and laboratory studies without jeopardising the eradication objective. Information gained on seed longevity, age to reproductive maturity, dispersal and control options has been used to direct survey and control activities. Planned and opportunistic data collections will continue to provide biological information to refine eradication activities

Rotator and extender ferroelectrics: Importance of the shear coefficient to the piezoelectric properties of domain-engineered crystals and ceramics

The importance of a high shear coefficient d15 (or d24) to the piezoelectric properties of domain-engineered and polycrystalline ferroelectrics is discussed. The extent of polarization rotation, as a mechanism of piezoelectric response, is directly correlated to the shear coefficient. The terms "rotator" and "extender" are introduced to distinguish the contrasting behaviors of crystals such as 4mm BaTiO3 and PbTiO3. In "rotator" ferroelectrics, where d15 is high relative to the longitudinal coefficient d33, polarization rotation is the dominant mechanism of piezoelectric response; the maximum longitudinal piezoelectric response is found away from the polar axis. In "extender" ferroelectrics, d15 is low and the collinear effect dominates; the maximum piezoelectric response is found along the polar axis. A variety of 3m, mm2 and 4mm ferroelectrics, with various crystal structures based on oxygen octahedra, are classified in this way. It is shown that the largest piezoelectric anisotropies d15/d33 are always found in 3m crystals; this is a result of the intrinsic electrostrictive anisotropy of the constituent oxygen octahedra. Finally, for a given symmetry, the piezoelectric anisotropy increases close to ferroelectric-ferroelectric phase transitions; this includes morphotropic phase boundaries and temperature induced polymorphic transitions.Comment: accepted in J. Appl. Phy

Increased options for controlling mikania vine (Mikania micrantha) with foliar herbicides

Mikania micrantha Kunth (mikania vine) is a highly invasive tropical weed that was first discovered in Australia in 1997, and has been the target of a nationally cost-shared weed eradication program since 2003. Field crews have been effectively treating the weed with herbicide solutions containing 1 g a.i. L−1 of fluroxypyr. During the eradication program there have been limited opportunities to test alternative foliar herbicides or rates. A newly discovered infestation provided sufficient immature vines to compare the effectiveness of eight herbicide treatments

Increased options for controlling mikania vine (Mikania micrantha) with foliar herbicides

Mikania micrantha Kunth (mikania vine) is a highly invasive tropical weed that was first discovered in Australia in 1997, and has been the target of a nationally cost-shared weed eradication program since 2003. Field crews have been effectively treating the weed with herbicide solutions containing 1 g a.i. L−1 of fluroxypyr. During the eradication program there have been limited opportunities to test alternative foliar herbicides or rates. A newly discovered infestation provided sufficient immature vines to compare the effectiveness of eight herbicide treatments

Advancing splatter gun technology for rangeland weeds

To determine whether more rangeland weeds could be susceptible to low-volume highconcentration herbicide applications (e.g., splatter guns), trials were initiated on gamba grass (Andropogon gayanus), rubber vine (Cryptostegia grandiflora), prickly acacia (Vachellia nilotica), and Chinee apple (Ziziphus mauritiana). For gamba grass, a rate response trial (0, 9, 18, 27, 36, 45 and 54 g a.i./L of mixture) of glyphosate has shown that 100% mortality can be achieved at rates ≥ 36 g a.i./L of mixture. A rubber vine trial is comparing the effect of timing of applications (between December and May) of two herbicides. Six months after treatment (MAT), Grazon™ Extra (triclopyr/picloram/aminopyralid) recorded the highest (i.e. December application) but most variable efficacy (0-80%) compared to 40-70% for Brush-off® (metsulfuron-methyl). The optimum way to spray plants using Hotshot™ (aminopyralid/fluroxypyr) is being investigated in a prickly acacia trial. Preliminary results, six MAT suggest that more severe damage occurs if the amount applied is calculated on the basis of the whole surface area of plants (i.e. both sides), but spraying from one side appears to be sufficient. For Chinee apple, a screening trial of five herbicides and two rates is showing that Brush-off® (metsulfuron-methyl) and Stinger™ (aminopyralid/metsulfuron-methyl) are the best performing herbicides, but only on smaller plants (< 2 m high) and at the highest applied rates 12 MAT. While promising, the variability in results indicates that many factors may affect efficacy, including the health, size and density of plants, herbicide choice and mixture/application rate, presence/absence of biological control agents and climatic conditions

Management options for gamba grass (Andropogon gayanus) in conservation areas of Cape York Peninsula Final report

Andropogon gayanus (gamba grass) is a high-biomass grass native to tropical and subtropical Africa and introduced into Australia as a pasture grass. Under well-managed grazing conditions, gamba grass has proven a useful and palatable addition to tropical cattle pastures. However, it has also become a significant environmental weed and is considered an ecosystem transformer. In recognition of the significant threat posed by gamba grass, it has been listed (along with 4 other invasive grasses) as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). One of the major problems limiting the effective management of gamba grass once established as an environmental weed is the lack of registered herbicides for use in natural systems and conservation areas. Glyphosate is the primary herbicide in use in northern Australia. There are several current and emerging issues which make a reliance on glyphosate for gamba grass control problematic. Application of glyphosate is logistically difficult in wet and remote areas, it has no residual action and largely relies on follow-up treatments, and there are emerging resistance issues. In addition, there is growing concern that glyphosate may be linked to carcinogenicity, genotoxicity and epidemiological disorders. Alternative herbicides are critical to allow long-term, effective and timely control of gamba grass in the environments encountered on Cape York Peninsula and across northern Australia. The goal of this project was to collate existing knowledge related to control and management of gamba grass and test alternative herbicide options for use in natural areas of Cape York Peninsula. Three herbicides were tested alongside glyphosate in field trials and 10 residual pre-emergence herbicides were tested in pot trials. Neither the field nor pot trials identified a clear suitable alternative to glyphosate that selectively controlled gamba grass with low off-target effects in the contexts in which we tested them. However, there are several herbicides that warrant further testing at a range of additional application rates and in a range of environments (flupropanate, clomazone, oxyfluorfen, imazapyr and indaziflam). In particular, the granular form of flupropanate is worthy of further experimentation because of its portability in the field and flexibility in application, and because it showed the most promising results in the field trials. Ultimately, land managers may need to trade-off significant, short-term, off-target effects for longer term, more effective and permanent control of gamba grass with herbicides

The Structural Complexity of (Bi0.5Na0.5)TiO3-BaTiO3 as Revealed by Raman Spectroscopy

The structural phase diagram of the Pb-free ferroelectric (Na1/2Bi1/2)1-xBaxTiO3 (NBT-BT), x<0.1, has been explored by Raman spectroscopy at temperatures from 10 to 470 K. The data provide clear evidence for a proposed temperature-independent morphotropic phase boundary at x \approx 0.055. However, there is no evidence for a structural phase transition across T \approx 370 K for x > 0.055, where bulk-property anomalies appear to signal a transition to a nonpolar or antiferroelectric phase. The results identify that the phase above 370 K shows short-range ionic displacements that are identical to those in the long-range-ordered phase below 370 K. These conclusions provide a natural interpretation of the weak piezoelectric response in this system and have important implications for the search for Pb-free piezoelectrics.Comment: 21 pages, 5 figure