Fe on molecular-layer MoS2 as inorganic Fe-S-2-Mo motifs for light-driven nitrogen fixation to ammonia at elevated temperatures
Chem Catalysis Cell Press 1:1 (2021) 162-182
Abstract:
Current industrial production of ammonia from the Haber-Bosch process and its transport concomitantly produces a large quantity of CO2. Herein, we successfully synthesize inorganic-structure-based catalysts with [Fe-S2-Mo] motifs with a connecting structure similar to that of FeMoco (a cofactor of nitrogenase) by placing iron atoms on a single molecular layer of MoS2 at various loadings. This type of new catalytic material functionally mimics the nitrogenase to convert N2 to ammonia and hydrogen in water without adding any sacrificial agent under visible-light illumination. Using the elevated temperature boosts the ammonia yield and the energy efficiency by one order of magnitude. The solar-to-NH3 energy-conversion efficiency can be up to 0.24% at 270°C, which is the highest efficiency among all reported photocatalytic systems. This method of ammonia production and the photocatalytic materials may open up an exciting possibility for the decentralization of ammonia production for fertilizer provision to local farmlands using solar illumination.Classical Spin Liquid or Extended Critical Range in h-YMnO_{3}?
Physical review letters 126:10 (2021) 107203
Abstract:
Neutron spectroscopy on the classical triangular-lattice frustrated antiferromagnet h-YMnO_{3} reveals diffuse, gapless magnetic excitations present both far below and above the ordering temperature. The correlation length of the excitations increases as the temperature approaches zero, bearing a strong resemblance to critical scattering. We model the dynamics in the ordered and correlated disordered phase as critical spin correlations in a two-dimensional magnetic state. We propose that our findings may provide a general framework to understand features often attributed to classical spin liquids.Crystallographic, optical, and electronic properties of the Cs2AgBi1-xInxBr6 double perovskite: understanding the fundamental photovoltaic efficiency challenges
ACS Energy Letters American Chemical Society 6:3 (2021) 1073-1081
Abstract:
We present a crystallographic and optoelectronic study of the double perovskite Cs2AgBi1–xInxBr6. From structural characterization we determine that the indium cation shrinks the lattice and shifts the cubic-to-tetragonal phase transition point to lower temperatures. The absorption onset is shifted to shorter wavelengths upon increasing the indium content, leading to wider band gaps, which we rationalize through first-principles band structure calculations. Despite the unfavorable band gap shift, we observe an enhancement in the steady-state photoluminescence intensity, and n-i-p photovoltaic devices present short-circuit current greater than that of neat Cs2AgBiBr6 devices. In order to evaluate the prospects of this material as a solar absorber, we combine accurate absorption measurements with thermodynamic modeling and identify the fundamental limitations of this system. Provided radiative efficiency can be increased and the choice of charge extraction layers are specifically improved, this material could prove to be a useful wide band gap solar absorber.Bond-dependent exchange, order-by-disorder and nodal quasiparticles' intensity signature in a honeycomb cobaltate
University of Oxford (2021)
Abstract:
Recent theoretical proposals have argued that cobaltates with edge-sharing octahedral coordination can have significant bond-dependent exchange couplings thus offering a platform in 3d ions for such physics beyond the much-explored realizations in 4d and 5d materials. Here we present high-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO3 revealing the presence of a finite energy gap and demonstrate that this implies the presence of bond-dependent anisotropic couplings. We also show through an extensive theoretical analysis that the gap further implies the existence of a quantum order-by-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations. Our data also provide an experimental observation of a universal winding of the scattering intensity in angular scans around linear band-touching points for both magnons and dispersive spin-orbit excitons, which is directly related to the non-trivial topology of the quasiparticle wavefunction in momentum space near nodal points. The deposited data package contains neutron powder diffraction and single crystal inelastic neutron scattering data to probe the magnetic ordering and dynamics. The zip archive contains the data in the format of multi-column ASCII files, a README.txt that explains the content of all the files and matlab code to plot the data in all the files, together with relevant RGB colourmap.Author Correction: Polarizing an antiferromagnet by optical engineering of the crystal field
Nature Physics Springer Nature 16:12 (2020) 1238-1238