Incorporating finite temperature into materials by design for nonstoichiometric complex functional oxides

Enabled by dramatic advancements in computational capabilities and the tightening integration of theory and experiment, materials by design is rapidly becoming a leading paradigm in materials science. However, to most effectively accelerate the pace of materials design and discovery, first-principles calculations must move closer to experimental reality by taking into account the finite temperature effects corresponding to typical growth and/or operating conditions. Our work aims to develop capabilities to incorporate these finite temperature effects, which include atomic and magnetic disorder as well as the temperature dependence of the free energies of solids, into modern materials by design. Please click Additional Files below to see the full abstract

The polymerisation of oligo(ethylene glycol methyl ether) methacrylate from a multifunctional poly(ethylene imine) derived amide: a stabiliser for the synthesis and dispersion of magnetite nanoparticles

A facile synthetic route to poly(ethylene imine)-graft-poly(oligo(ethylene glycol methyl ether)) (PEI-graft-POEGMA) functionalised superparamagnetic magnetite nanoparticles is described. The polymerisation of OEGMA from a model molecular amide demonstrated the feasibility of POEGMA synthesis under mild ATRP conditions (20 °C in ethanol) albeit with low initiator efficiencies. DFT studies suggest that the amide functionality is intrinsically of lower activity than ester functional monomers and initiators for atom transfer polymerisation (ATRP) as a consequence of higher bond dissociation energies and bond dissociation free energies (BDFE). However these studies further highlighted that use of an appropriate solvent could reduce the free energy of dissociation thereby reducing the relative difference in BDFE between the ester and amide groups. A commercial branched PEI sample was functionalised by reaction with 2-bromo-2-methylpropanoyl bromide giving an amide macroinitiator suitable for the atom transfer radical polymerisation (ATRP) of oligo(ethylene glycol methyl ether) methacrylate. The resulting PEI-graft-POEGMA copolymers were characterised by SEC, FT-IR and 1H and 13C NMR spectroscopy. PEI-graft-POEGMA coated magnetite nanoparticles were synthesised by a basic aqueous co-precipitation method and were characterised by transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry and dynamic light scattering. These copolymer coated magnetite nanoparticles were demonstrated to be effectively stabilised in an aqueous medium. Overall the particle sizes and magnetic and physical properties of the coated samples were similar to those of uncoated samples

Passive UHF RFID Voice Prosthesis Mounted Sensor for Microbial Growth Detection

Capacitive loading due to human tissue can lead to low efficiency for implantable Passive Radio Frequency Identification (RFID) antennas. The presented passive UHF antenna sensor provides read distances above 0.5 meters (within a body phantom) by utilizing a convoluted half-wave dipole design. It is able to detect simulated early to mature Candida albicans biofilm growth when mounted upon a voice prosthesis (up to a 30 μm biofilm thickness). Depending on the propagation frequency of interest, as early 4-hour growth (5 to 10 μm biofilm thickness) equivalent could be detected and before any device failure could occur due to the colonization. This was accomplished by utilising thin layers of polyurethane to decouple the saliva from the presented UHF sensor (biofilm growth is known to increase layer hydrophobicity). This presented sensor has better functionality within the US UHF frequency band as it detects changes above 5 μm. If there is a need for implantation within additional tissues with variable dielectric properties, a shunt capacitance of 2.6 pF could allow the system functionality within the permittivity range of 21 to 58. Allowing for immediate medical intervention before medical prosthesis failur

Ternary Nitride Semiconductors in the Rocksalt Crystal Structure

Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optoelectronic devices. In contrast, rocksalt-based nitrides are known for their metallic and refractory properties. Breaking this dichotomy, here we report on ternary nitride semiconductors with rocksalt crystal structures, remarkable optoelectronic properties, and the general chemical formula Mg$_{x}$TM$_{1-x}$N (TM=Ti, Zr, Hf, Nb). These compounds form over a broad metal composition range and our experiments show that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8-2.1 eV). Lattice parameters are compatible with growth on a variety of substrates, and epitaxially grown MgZrN$_{2}$ exhibits remarkable electron mobilities approaching 100 cm$^{2}$V$^{-1}$s$^{-1}$. Ab initio calculations reveal that these compounds have disorder-tunable optical properties, large dielectric constants and low carrier effective masses that are insensitive to disorder. Overall, these experimental and theoretical results highlight Mg$_{G-3}$TMN$_{G-2}$ rocksalts as a new class of semiconductor materials with promising properties for optoelectronic applications

A Map of the Inorganic Ternary Metal Nitrides

Exploratory synthesis in novel chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation--from which we experimentally realized 7 new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity, and covalency of solid-state bonding from the DFT-computed electron density, we reveal the complex interplay between chemistry, composition, and electronic structure in governing large-scale stability trends in ternary nitride materials