Towards engineering the perfect defect in high-performing permanent magnets

Permanent magnets draw their properties from a complex interplay, across multiple length scales, of the composition and distribution of their constituting phases, that act as building blocks, each with their associated intrinsic properties. Gaining a fundamental understanding of these interactions is hence key to decipher the origins of their magnetic performance and facilitate the engineering of better-performing magnets, through unlocking the design of the "perfect defects" for ultimate pinning of magnetic domains. Here, we deployed advanced multiscale microscopy and microanalysis on a bulk Sm2(CoFeCuZr)17 pinning-type high-performance magnet with outstanding thermal and chemical stability. Making use of regions with different chemical compositions, we showcase how both a change in the composition and distribution of copper, along with the atomic arrangements enforce the pinning of magnetic domains, as imaged by nanoscale magnetic induction mapping. Micromagnetic simulations bridge the scales to provide an understanding of how these peculiarities of micro- and nanostructure change the hard magnetic behaviour of Sm2(CoFeCuZr)17 magnets. Unveiling the origins of the reduced coercivity allows us to propose an atomic-scale defect and chemistry manipulation strategy to define ways toward future hard magnets

Morphology control and large piezoresponse of hydrothermally synthesized lead-free piezoelectric (Bi<inf>0.5</inf>Na<inf>0.5</inf>)TiO<inf>3</inf> nanofibres

Lead-free piezoelectric bismuth sodium titanate (BNT) nanostructures were synthesised using a low-temperature hydrothermal technique. It is found that the phase and morphology of the products are strongly dependent on the composition and concentration of the precursors, as well as the processing conditions. Through optimising the synthesis parameters, well-crystallized BNT nanofibers with 150-200 nm diameters and ∼5 μm length were obtained. The BNT fibres show a pure perovskite phase with (011) orientation along the length direction. A piezoelectric constant of d33 = ∼15 pm V-1 in the diameter direction was observed for these BNT nanofibers

Influence of microstructure on symmetry determination of piezoceramics

The origin of the complex reflection splitting in potassium sodium niobate doped with lithium and manganese was investigated using temperature-dependent high-resolution X-ray and neutron diffraction as well as electron probe microanalysis and scanning electron microscopy. Two structural models were developed from the diffraction data. A single-phase monoclinic Pm model is known from the literature and is able to reproduce the diffraction patterns perfectly. However, a model with phase coexistence of two classical orthorhombic Amm2 phases can also reproduce the diffraction data with equal accuracy. Scanning electron microscopy in combination with electron probe microanalysis revealed segregation of the A-site substituents potassium and sodium. This favours the model with phase coexistence and confirms the need for comprehensive analyses with complementary methods to cover a broad range of length scales as well as to assess both average and local structure

Proceedings of iCMEMS Conference 2017

Pyrolysis of coals to produce cokes is an important part of the ironmaking process. Coal pyrolysis to coke is an energy-intensive process and involves the transformation of the coal from a soft carbonaceousmaterial to a hard coking structure. During this process, volatiles present in the coke are released and coal tar is extracted, and this has numerous applications as a source of various chemicals for different industries as well as carbon for anodes. This work investigates the effect of blending different amounts and proportions of waste polymers with coals in order to enhance the coal tar yield and to modify the chemical product characteristics. Coal and polymer blends were pyrolysed at 500°C and the tar and volatile compounds were collected by condensation. The collected tars (solid and liquid) were characterised using gas chromatography-mass spectrometry (GC-MS) to determine the major components. Further analysis of the proportions of the major organic components was conducted using solution NMR analysis. When blended with the polymers, all the coals showed a proportional increase in their tar yields. The highest yields were observed with the addition of polystyrene (PS), followed by rubber tyres (RT), while polymers with aliphatic chains produced lower yields. This work has shown potential for enhancing the coal tar yield and for modifying coal tar properties through polymer addition, which can add further value by providing additional uses for pyrolysis products and by removing waste polymers from the disposal stream