Low temperature processing of solution-derived ceria deposits on flat surfaces of 3D-printed polyamide

Doped ceria deposits have been prepared on 3D-printed polyamide-12 components starting from inkjet-compatible solutions in an attempt to functionalize the surface of the plastic part, followed by a low temperature decomposition process at 160¿°C in air. The non-continuous deposits were characterized by simultaneous thermogravimetric analysis, differential scanning calorimetry and evolved gas analysis, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy and electron diffraction. After thermal treatment, the deposits are still clearly visible at the surface of the polymer. However, no crystallinity of the ceria is observed, in contrast to identical low temperature processing on inert substrates such as glass where nanoparticle ceria aggregates were produced. This is tentatively explained by the chemically-reducing character of the polyamide, and in particular to CO and hydrocarbon gases released during the heating process, which would continuously induce the reduction of Ce4+ to Ce3+ at the low temperature of 160¿°C, influencing the non-detection of crystalline ceria.Peer ReviewedPostprint (published version

Crystal structures of superconducting sodium intercalates of hafnium nitride chloride

Abstract Sodium intercalation compounds of HfNCl have been prepared at room temperature in naphtyl sodium solutions in tetrahydrofuran and their crystal structure has been investigated by Rietveld refinement using X-ray powder diffraction data and high-resolution electron microscopy. The structure of two intercalates with space group R3m and lattice parameters a = 3.58131(6) Å , c = 57.752(6) Å , and a = 3.58791(8) Å , c = 29.6785(17) Å is reported, corresponding to the stages 2 and 1, respectively, of Na x HfNCl. For the stage 2 phase an ordered model is presented, showing two crystallographically independent [HfNCl] units with an alternation of the Hf-Hf interlayer distance along the c-axis, according with the occupation by sodium atoms of one out of two van der Waals gaps. Both stages 1 and 2 phases are superconducting with critical temperatures between 20 and 24 K, they coexist in different samples with proportions depending on the synthesis conditions, and show a variation in c spacing that can be correlated with the sodium stoichiometry. High-resolution electron microscopy images of the host and intercalated samples show bending of the HfNCl bilayers as well as stacking faults in some regions, which coexist in the same crystal with ordered domains.

Controlling Magnetization Reversal and Hyperthermia Efficiency in Core-Shell Iron-Iron Oxide Magnetic Nanoparticles by Tuning the Interphase Coupling

Magnetic particle hyperthermia, in which colloidal nanostructures are exposed to an alternating magnetic field, is a promising approach to cancer therapy. Unfortunately, the clinical efficacy of hyperthermia has not yet been optimized. Consequently, routes to improve magnetic particle hyperthermia, such as designing hybrid structures comprised of different phase materials, are actively pursued. Here, we demonstrate enhanced hyperthermia efficiency in relatively large spherical Fe/Fe-oxide core-shell nanoparticles through the manipulation of interactions between the core and shell phases. Experimental results on representative samples with diameters in the range 30-80 nm indicate a direct correlation of hysteresis losses to the observed heating with a maximum efficiency of around 0.9 kW/g. The absolute particle size, the core-shell ratio, and the interposition of a thin wüstite interlayer are shown to have powerful effects on the specific absorption rate. By comparing our measurements to micromagnetic calculations, we have unveiled the occurrence of topologically nontrivial magnetization reversal modes under which interparticle interactions become negligible, aggregates formation is minimized and the energy that is converted into heat is increased. This information has been overlooked until date and is in stark contrast to the existing knowledge on homogeneous particles

Nitride tuning of lanthanide chromites

LnCrO3−xNx compounds with Ln = La, Pr and Nd represent one of the few examples of chromium oxynitrides and the first chromium oxynitride perovskites. Hole-doping of LnCrO3 through O2−/N3− anion substitution suppresses the antiferromagnetic transition far less drastically than cation substitutions.</p

Chemistry and high temperature superconductivity

Seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb3Ge have been discovered in the last 25 years. Each family is reviewed briefly and their common chemical features are discussed. High temperature superconductors are distinguished by having a high (\geq 50%) content of nonmetallic elements and fall into two broad classes. 'Metal-nonmetal' superconductors require a specific combination of elements such as Cu-O and Fe-As which give rise to the highest known Tc's, probably through a magnetic pairing mechanism. 'Nonmetal-bonded' materials contain covalently-bonded nonmetal anion networks and are BCS-like superconductors. Fitting an extreme value function to the distribution of Tc values for the known high-Tc families suggests that the probability of a newly discovered superconductor family having maximum Tc > 100 K is ~0.1-1%, decreasing to ~0.02-0.2% for room temperature superconductivity.Comment: To be published as a Feature Article in the Journal of Materials Chemistr

Expanding frontiers in materials chemistry and physics with multiple anions

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials

Thermally Robust Anion-Chain Order in Oxynitride Perovskites

The presence and thermal stability of anion order in the oxynitride perovskites SrTaO₂N and LaTaON₂ have been determined using high resolution powder neutron and electron diffraction data. Partial order of oxide and nitride anions consistent with the formation of planes of disordered <i>cis</i>-anion chains is observed in both materials, with a chemical symmetry between distributions in SrTaO₂N and LaTaON₂. No loss of anion order is observed up to 1100 °C and extrapolations based on lattice strains show the order to be stable to remarkably high temperatures >2000 °C, demonstrating that anions are segregated when the materials are synthesized. SrTaO₂N has an apparent tetragonal <i>I</i>4/<i>mcm</i> superstructure at room temperature due to ordered octahedral tilts, but anion order lowers symmetry to an orthorhombic <i>Fmmm</i> supercell (with lattice parameters <i>a</i> = 8.0657(8), <i>b</i> = 8.0614(7), and <i>c</i> = 8.0775(4) Å). Anion order also lowers the symmetry of LaTaON₂ from apparent orthorhombic <i>Imma</i> to monoclinic <i>I</i>2/<i>m</i> (<i>a</i> = 5.7140(6), <i>b</i> = 8.0595(6), <i>c</i> = 5.7506(5) Å, and β = 90.239(4)° at 20 °C) and this superstructure persists up to 1100 °C with an extrapolated loss of tilting at 1540 °C. Anion order appears to direct octahedral tilting such that the more rigid Ta–N–Ta bridges retain bond angles closer to 180° than the Ta–O–Ta connections in these superstructures