Determination of local crystal symmetry in complex, multielement, ferroelectric perovskites and alloys

Structural change arising from correlated lattice and charge interaction in complex, multi-element, crystals has a profound effect on their physical properties. Examples include charge ordering in complex oxides, polarization nanodomains in ferroelectrics, and vortex matter. A common scheme to these systems is that there exists a distinction between local crystal symmetry and the average, macroscopic symmetry imposed by fluctuations in the crystal lattice. Before we can control and exploit these fluctuation-induced emergent properties, the crucial first step is to fully characterize any correlation that may exist. This thesis explores the crystallographic aspect of local charge, polarization, and lattice interactions in complex, multi-element, crystals by developing scanning convergent beam electron diffraction (SCBED) based techniques. The applications of SCBED characterization demonstrated here include: ferroelectric BaTiO3 single crystal, relaxor-ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (x=0.08) single crystal, and multi-principal-element alloy Al0.1CrFeCoNi. First, we show the local crystal symmetry and polarization fluctuations in BaTiO3 single crystals as determined using SCBED. An improved algorithm for CBED symmetry quantification is used to map the ferroelectric domains and local symmetry across the ferroelectric phase transition temperatures. The symmetry in BaTiO3 was found inhomogeneous; regions of a few tens of nanometers retaining almost perfect symmetry are interspersed in regions of lower symmetry. The SCBED results suggest the coexistence of displacive and order-disorder phase transition, affected upon by the local structure. Next, we examine the local symmetry, polarization nanodomains, and the domain wall (DW) structures in relaxor-ferroelectrics. Nanometer-sized domains having the monoclinic Pm symmetry in PZN-8%PT single crystals are identified by performing SCBED along the [100], [001], and [111] zone axes. Intensity distribution in the (000) disks in the CBED patterns is used to determine lattice-rotation at the precision of ±0.012° by performing SCBED on a standard Si sample. A careful examination of the polarization DWs revealed the presence of lattice-rotation vortices of ~15nm in diameter in PZN-8%PT, which can be attributed to bound charge discontinuity and depolarization fields. The lattice distortion effect in high entropy alloys (HEAs) is explored as a model of multi element alloys. Lattice distortion is one of the four core effects of HEAs, which results from different atom sizes and influences solid solution hardening. However, so far quantification of lattice distortion effects by X-ray and neutron diffraction has provided contradictory results. Using SCBED, we visualize the sub-nanometer strain fluctuations and local symmetry breaking in single phase Al0.1CrFeCoNi. Our results reveal 10±3nm, disc-shaped, clusters having ~7.1% tensile displacements along directions distributed throughout the specimen; local strain, on the contrary, was found to be fluctuating within ±1.3% and slow-varying over ~50nm. The observed inhomogeneous lattice distortion using scanning electron diffraction thus provides a new perspective on structure and property relations in multi-principal-element systems

A hybrid pulsed laser deposition approach to grow thin films of chalcogenides

Vapor-pressure mismatched materials such as transition metal chalcogenides have emerged as electronic, photonic, and quantum materials with scientific and technological importance. However, epitaxial growth of vapor-pressure mismatched materials are challenging due to differences in the reactivity, sticking coefficient, and surface adatom mobility of the mismatched species constituting the material, especially sulfur containing compounds. Here, we report a novel approach to grow chalcogenides - hybrid pulsed laser deposition - wherein an organosulfur precursor is used as a sulfur source in conjunction with pulsed laser deposition to regulate the stoichiometry of the deposited films. Epitaxial or textured thin films of sulfides with variety of structure and chemistry such as alkaline metal chalcogenides, main group chalcogenides, transition metal chalcogenides and chalcogenide perovskites are demonstrated, and structural characterization reveal improvement in thin film crystallinity, and surface and interface roughness compared to the state-of-the-art. The growth method can be broadened to other vapor-pressure mismatched chalcogenides such as selenides and tellurides. Our work opens up opportunities for broader epitaxial growth of chalcogenides, especially sulfide-based thin film technological applications.Comment: 27 page

Smooth, homogeneous, high-purity Nb3Sn superconducting RF resonant cavity by seed-free electrochemical synthesis

Workbench-size particle accelerators, enabled by Nb3Sn-based superconducting radio-frequency (SRF) cavities, hold the potential of driving scientific discovery by offering a widely accessible and affordable source of high-energy electrons and X-rays. Thin-film Nb3Sn RF superconductors with high quality factors, high operation temperatures, and high-field potentials are critical for these devices. However, surface roughness, non-stoichiometry, and impurities in Nb3Sn deposited by conventional Sn-vapor diffusion prevent them from reaching their theoretical capabilities. Here we demonstrate a seed-free electrochemical synthesis that pushes the limit of chemical and physical properties in Nb3Sn. Utilization of electrochemical Sn pre-deposits reduces the roughness of converted Nb3Sn by five times compared to typical vapor-diffused Nb3Sn. Quantitative mappings using chemical and atomic probes confirm improved stoichiometry and minimized impurity concentrations in electrochemically synthesized Nb3Sn. We have successfully applied this Nb3Sn to the large-scale 1.3 GHz SRF cavity and demonstrated ultra-low BCS surface resistances at multiple operation temperatures, notably lower than vapor-diffused cavities. Our smooth, homogeneous, high-purity Nb3Sn provides the route toward high efficiency and high fields for SRF applications under helium-free cryogenic operations

Electroplating lithium transition metal oxides.

Materials synthesis often provides opportunities for innovation. We demonstrate a general low-temperature (260°C) molten salt electrodeposition approach to directly electroplate the important lithium-ion (Li-ion) battery cathode materials LiCoO2, LiMn2O4, and Al-doped LiCoO2. The crystallinities and electrochemical capacities of the electroplated oxides are comparable to those of the powders synthesized at much higher temperatures (700° to 1000°C). This new growth method significantly broadens the scope of battery form factors and functionalities, enabling a variety of highly desirable battery properties, including high energy, high power, and unprecedented electrode flexibility

Blockchain-Based Medical Record Management with Biofeedback Information

Blockchain is a new emerging technology of distributed databases, which guarantees the integrity, security and incorruptibility of data by means of the cryptography. Such features are suitable for secure and reliable data storage. This chapter investigates the blockchain-based architecture with applications to medical health record or biofeedback information management. This framework employs the smart contract to establish a medical record management system to ensure the privacy of patients. Moreover, the blockchain technique accelerates the medical record or information exchange such that the cost of human resource is significant reduced. All patients can manage their individual medical records and information easily in the different hospitals and clinics. They also have the privilege to deal with and authorize personal medical records in the proposed management framework

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data