Demonstration of Elemental Partitioning During Austenite Formation in Low-Carbon Aluminium alloyed steel

This work investigates the influence of aluminium, in solid solution, on austenite formation in a lowcarbon aluminium alloyed (0.48 wt. %) steel during continuous heating. A thin section across an untransformed ferrite and austenite interface was prepared for transmission electron microscopy by focused ion beam milling. Microstructural characterization using imaging and elemental analysis demonstrates that aluminium partitions from austenite to ferrite during very slow heating conditions, stabilizing this latter phase and shifting the final transformation temperature for austenite formation (Ac3)Peer reviewe

Demonstration of Elemental Partitioning During Austenite Formation in Low-Carbon Aluminium alloyed steel

This work investigates the influence of aluminium, in solid solution, on austenite formation in a lowcarbon aluminium alloyed (0.48 wt. %) steel during continuous heating. A thin section across an untransformed ferrite and austenite interface was prepared for transmission electron microscopy by focused ion beam milling. Microstructural characterization using imaging and elemental analysis demonstrates that aluminium partitions from austenite to ferrite during very slow heating conditions, stabilizing this latter phase and shifting the final transformation temperature for austenite formation (Ac3)Peer reviewe

Ferroelectric Behavior in Exfoliated 2D Aurivillius Oxide Flakes of Sub‐Unit Cell Thickness

Ferroelectricity in ultrasonically exfoliated flakes of the layered Aurivillius oxide Bi5Ti3Fe0.5Co0.5O15 with a range of thicknesses is studied. These flakes have relatively large areas (linear dimensions many times the film thickness), thus classifying them as 2D materials. It is shown that ferroelectricity can exist in flakes with thicknesses of only 2.4 nm, which equals one‐half of the normal crystal unit cell. Piezoresponse force microscopy (PFM) demonstrates that these very thin flakes exhibit both piezoelectric effects and that the ferroelectric polarization can be reversibly switched. A new model is presented that permits the accurate modeling of the field‐on and field‐off PFM time domain and hysteresis loop responses from a ferroelectric during switching in the presence of charge injection, storage, and decay through a Schottky barrier at the electrode–oxide interface. The extracted values of spontaneous polarization, 0.04(±0.02) C m−2 and electrostrictive coefficient, 2(±0.1) × 10−2 m4 C−2 are in good agreement with other ferroelectric Aurivillius oxides. Coercive field scales with thickness, closely following the semi‐empirical scaling law expected for ferroelectric materials. This constitutes the first evidence for ferroelectricity in a 2D oxide material, and it offers the prospect of new devices that might use the useful properties associated with the switchable ferroelectric spontaneous polarization in a 2D materials format

Electric-field-induced phase switching in textured Ba-doped bismuth ferrite lead titanate

The template grain growth technique was used to synthesis textured 60BiFeO3-PbTiO3 (60'40BFPT) by using platelets of BaTiO3 as template. Synchrotron measurement clearly showed textured 60'40BFPT. Moreover, in situ high energy synchrotron radiation was employed to investigate the influence of an external electric filed on crystallographic structure of mixed phase 60:40BFPT. Application of an electric field ≥ 1 kV/mm resulted in phase transformation from mixed rhombohedral/tetragonal phases (≈ 73.5% tetragonal / 26.5% rhombohedral) to predominately tetragonal phase (≈ 95%) at applied field of 6 kV/mm

Texture analysis of thick bismuth ferrite lead titanate layers

The template grain growth technique was used to synthesis textured 60BiFeO3-PbTiO3(60:40BFPT) by using platelets of BaTiO3 as template. Synchrotron measurement clearly showed textured 60:40BFPT. Moreover, in situ high energy synchrotron radiation was employed to investigate the influence of an external electric filed on crystallographic structure of mixed phase 60:40BFPT. Application of an electric field ≥ 1 kV/mm resulted in phase transformation from mixed rhombohedral/tetragonal phases (≈ 73.5% tetragonal / 26.5% rhombohedral) to predominately tetragonal phase (≈ 95%) at applied field of 6 kV/mm. A crystallographic texture refinement was done by using software package materials analysis using diffraction (MAUD) with a 4th order spherical harmonic orientation distribution function (ODF). This refinement was completed using a P4mm+Cm structure model. Texture coefficients were constrained such that the equivalent texture coefficients of each phase are the same. The resulting texture refinement determined that sample has a 1.3 multiples of random distribution (MRD) {100} crystallographic texture

Observation of thermally etched grain boundaries with the FIB/TEM technique

Thermal etching is a method which is able to reveal and characterize grain boundaries, twins or dislocation structures and determine parameters such as grain boundary energies, surface diffusivities or study phase transformations in steels, intermetallics or ceramic materials. This method relies on the preferential transfer of matter away from grain boundaries on a polished sample during heating at high temperatures in an inert/vacuum atmosphere. The evaporation/diffusion of atoms at high temperatures results in the formation of grooves at the intersections of the planes of grain/twin boundaries with the polished surface. This work describes how the combined use of Focussed Ion Beam and Transmission Electron Microscopy can be used to characterize not only the grooves and their profile with the surface, but also the grain boundary line below the groove, this method being complementary to the commonly used scanning probe techniques

Crystallographic and magnetic investigations of textured bismuth ferrite lead titanate layers

In present work we demonstrate the synthesis of textured 60BiFeO3–40PbTiO3 (60:40 BFPT) by using the templated grain growth technique with platelets of BaTiO3. Synthesised 60:40 BFPT has been examined by High-energy x-ray diffraction utilizing a synchrotron x-ray source. The crystallographic structure refinement results revealed the co-existence of monoclinic and tetragonal phases. By employing an external electric field, the mixed monoclinic/tetragonal phases transformed to the predominantly tetragonal phase. In addition, a crystallographic texture refinement was completed on unpoled state of 60:40 BFPT which showed the sample had 1.3 multiples of random distribution (MRD) {100} crystallographic textured in tetragonal phase. However, magnetic measurements showed isotropic ferromagnetism for the sample which is not in agreement with the crystallographic texture properties of the sample. Low temperature magnetic transition has been found in zero field cooled—field cooled (ZFC-FC) measurements. This could be due to the possible existence of a secondary magnetic phase, which dominated the magnetic result

Characterization of thick bismuth ferrite-lead titanate films processed by tape casting and templated grain growth

The templated grain growth technique was used to synthesise textured 60BiFeO3–40PbTiO3 (60:40BFPT). Both Aurivillius (Bi4Ti3O12, PbBi4Ti4O15) and perovskite templates (BaTiO3, SrTiO3) were used to prepare 60:40BFPT. Only BaTiO3 templates were found to successful impart a texture to the ceramic matrix. In the case of perovskite templates, ferroelectricity was evident from saturated polarisation hysteresis loops. Saturated polarisation loops were achieved due to the substitution of Ba2+ or Sr2+, which reduces the coercive field. SrTiO3 and BaTiO3 templated ceramics showed remanent polarisation of 30 and 36 μC/cm2, respectively. Aurivillius templates did not generate ferroelectric materials. Because of their high chemical stability in this system, BaTiO3 templates appear to be the best candidate for fabricating textured BFPT by the reactive templated grain growth method