Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics

Oxide materials which exhibit both ferroelectricity and ferromagnetism are of great interest for sensors and memory applications. Layered bismuth titanates with an Aurivillius structure, (BiFeO3)nBi4Ti3O12, can possess ferroelectric and ferromagnetic order parameters simultaneously. It has recently been demonstrated that one such example, Bi5Fe0.5Co0.5Ti3O15,where n = 1 with half the Fe3+ sites substituted by Co3+ ions, exhibits both ferroelectric and ferromagnetic properties at room temperature. Here we report the fabrication of highly-oriented polycrystalline ceramics of this material, prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets. Electron backscatter images showed that there is a secondary phase within the ceramic matrix which is rich in cobalt and iron, hence this secondary phase could contribute in the main phase ferromagnetic property. The concentration of the secondary phase obtained from secondary electron microscopy is estimated at less than 2.5 %, below the detection limit of XRD. TEM was used to identify the crystallographic structure of the secondary phase, which was shown to be cobalt ferrite, CoFe2O4. It is inferred from the data that the resultant ferromagnetic response identified using VSM measurements was due to the presence of the minor secondary phase. The Remanent magnetization at room temperature was Mr ≈ 76 memu/g which dropped down to almost zero (Mr ≈ 0.8 memu/g) at 460 oC, far lower than the anticipated for CoFe2O4

Microstructure development of BiFeO3-PbTiO3 films deposited by pulsed laser deposition on platinum substrates

BiFeO3-PbTiO3 films around the morphotropic phase boundary were deposited by pulsed laser deposition on polycrystalline Pt/TiOx/SiO2/Si substrates. X-ray analysis confirms that 0.6BiFeO3-0.4PbTiO3 films are (0 0 1) tetragonal preferentially orientated due to lattice matching with the underlying substrate. The misfit strain at the substrate-film interface is relieved by a ∼19% orientation transformation from (0 0 1) to (1 0 0) due to the lattice mismatch at the substrate-film interface and the difference in thermal expansion coefficients of the substrate and deposited film. 0.7BiFeO3-0. 3PbTiO3 films are mixed-phase rhombohedral-tetragonal with (0 0 1)/(1 1 1) preferential orientation due to the lattice match to the (1 1 1) and (1 0 0) of the underlying platinum as well as to being close to the morphotropic phase boundary. Inconsistent structural and electrical properties in reported BiFeO3-PbTiO3 films are explained in terms of film morphology and diffusion of bismuth into platinum. Films below ∼220 nm thickness produce short circuits due to a Volmer-Weber growth mechanism which results in physical defects within the films. Films above this critical thickness also produce variable electrical properties due to diffusion of bismuth into the underlying platinum electrode which has been confirmed by energy dispersive X-ray spectroscopy

Combinatorial microfluidic droplet engineering for biomimetic material synthesis

Although droplet-based systems are used in a wide range of technologies, opportunities for systematically customizing their interface chemistries remain relatively unexplored. This article describes a new microfluidic strategy for rapidly tailoring emulsion droplet compositions and properties. The approach utilizes a simple platform for screening arrays of droplet-based microfluidic devices and couples this with combinatorial selection of the droplet compositions. Through the application of genetic algorithms over multiple screening rounds, droplets with target properties can be rapidly generated. The potential of this method is demonstrated by creating droplets with enhanced stability, where this is achieved by selecting carrier fluid chemistries that promote titanium dioxide formation at the droplet interfaces. The interface is a mixture of amorphous and crystalline phases, and the resulting composite droplets are biocompatible, supporting in vitro protein expression in their interiors. This general strategy will find widespread application in advancing emulsion properties for use in chemistry, biology, materials and medicine

BMC Ophthalmol

BACKGROUND: This was an updated network meta-analysis (NMA) of anti-vascular endothelial growth factor (VEGF) agents and laser photocoagulation in patients with diabetic macular edema (DME). Unlike previous NMA that used meta-regression to account for potential confounding by systematic variation in treatment effect modifiers across studies, this update incorporated individual patient-level data (IPD) regression to provide more robust adjustment. METHODS: An updated review was conducted to identify randomised controlled trials for inclusion in a Bayesian NMA. The network included intravitreal aflibercept (IVT-AFL) 2 mg bimonthly (2q8) after 5 initial doses, ranibizumab 0.5 mg as-needed (PRN), ranibizumab 0.5 mg treat-and-extend (T&E), and laser photocoagulation. Outcomes included in the analysis were change in best-corrected visual acuity (BCVA), measured using an Early Treatment Diabetic Retinopathy Study (ETDRS) chart, and patients with >/=10 and >/= 15 ETDRS letter gains/losses at 12 months. Analyses were performed using networks restricted to IPD-only and IPD and aggregate data with (i) no covariable adjustment, (ii) covariable adjustment for baseline BVCA assuming common interaction effects (against reference treatment), and (iii) covariable adjustments specific to each treatment comparison (restricted to IPD-only network). RESULTS: Thirteen trials were included in the analysis. IVT-AFL 2q8 was superior to laser in all analyses. IVT-AFL 2q8 showed strong evidence of superiority (95% credible interval [CrI] did not cross null) versus ranibizumab 0.5 mg PRN for mean change in BCVA (mean difference 5.20, 95% CrI 1.90-8.52 ETDRS letters), >/=15 ETDRS letter gain (odds ratio [OR] 2.30, 95% CrI 1.12-4.20), and >/=10 ETDRS letter loss (OR 0.25, 95% CrI 0.05-0.74) (IPD and aggregate random-effects model with baseline BCVA adjustment). IVT-AFL 2q8 was not superior to ranibizumab 0.5 mg T&E for mean change in BCVA (mean difference 5.15, 95% CrI -0.26-10.61 ETDRS letters) (IPD and aggregate random-effects model). CONCLUSIONS: This NMA, which incorporated IPD to improve analytic robustness, showed evidence of superiority of IVT-AFL 2q8 to laser and ranibizumab 0.5 mg PRN. These results were irrespective of adjustment for baseline BCVA

Pressure induced para-antiferromagnetic switching in BiFeO -PbTiO as determined using in-situ neutron diffraction

BiFeO-PbTiO exhibits both ferroelectric and antiferromagnetic order, depending on the composition. Moderate hydrostatic pressures have been used at room temperature to transform the crystallographic phase from P4mm to R3c for the compositions 0.7BiFeO-0.3PbTiO and 0.65BiFeO-0.35PbTiO, as determined using in-situ neutron diffraction. Using Rietveld refinements, the resultant data showed that, for both compositions, a transformation from para- to G-type antiferromagnetic order accompanied the structural transition. The transformation occurred over the range 0.4-0.77 and 0.67-0.88 GPa for 0.7BiFeO-0.3PbTiO and 0.65BiFeO-0. 35PbTiO, respectively; at intermediate pressures, a mixture of P4mm and R3c phases were evident. These pressures are far lower than required to induce a phase transition in either the BiFeO or PbTiO end members. The driving force for this pressure induced first order phase transition is a significant difference in volume between the two phases, P4mm > R3c of 4-5, at ambient pressure. Upon removal of the pressure, 0.65BiFeO-0.35PbTiO returned to the paramagnetic tetragonal state, whereas in 0.7BiFeO-0.3PbTiO antiferromagnetic ordering persisted, and the structural phase remained rhombohedral. Using conventional laboratory x-ray diffraction with a hot-stage, the phase readily reverted back to a tetragonal phase, at temperatures between 100 and 310 °C for 0.7BiFeO-0.3PbTiO, far lower than the ferroelectric Curie point for this composition of 632 °C. To our knowledge, the reported pressure induced para- to antiferromagnetic transition is unique in the literature

LiNb03 polymer composite thin film: towards it's preparation

Lithium Niobate (LiNbO3) is a well-known ferroelectric material with excellent nonlinear piezoelectric, pyroelectric and electro-optic properties. However, there is little research conducted exploring its application in thin film composites. Here we describe the preparation and characterization of LiNbO3 , as a precursor to its use in polymer composites. LiNbO3 has been prepared via a molten salt route, which has been previously shown to be one of the simplest means to prepare pure and stoichiometric LiNbO3 nanocrystals