Stuffed Rare-Earth Garnets

We report the synthesis and magnetic characterization of stuffed rare-earth gallium garnets, RE3+xGa5–xO12 (RE = Lu, Yb, Er, Dy, Gd), for x up to 0.5. The excess rare-earth ions partly fill the octahedral sites normally fully occupied by Ga3+, forming disordered pairs of corner-shared face-sharing magnetic tetrahedra. The Curie–Weiss constants and observed effective moments per rare-earth are smaller than are seen for the unstuffed gallium garnets. No significant change in the field-dependent magnetization is observed but missing entropy is seen when integrating the heat capacity down to 0.5 K

Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides

LaxSr2–xNiRuO6, LaxSr4–xNiRuO8, and LaxSr3–xNiRuO7 are, respectively, the n = ∞, 1, and 2 members of the (Lax/2Sr1–(x/2))nSr­(Ni0.5Ru0.5)nO3n+1 compositional series. Reaction with CaH2, in the case of the LaxSr2–xNiRuO6 perovskite phases, or Zr oxygen getters in the case of the LaxSr4–xNiRuO8 and LaxSr3–xNiRuO7 Ruddlesden–Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1–(x/2))nSr­(Ni0.5Ru0.5)nO3n–1 compounds (LaxSr2–xNiRuO4, LaxSr4–xNiRuO6, and LaxSr3–xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+ and Ru2+ centers they contain. Increasing the La3+ concentration (x > 1) leads to a reduction of some of the Ru2+ centers to Ru1+ centers and a suppression of the ferromagnetic state (lower Tc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+ concentration (x < 1) oxidizes some of the Ru2+ centers to Ru3+ centers and enhances the ferromagnetic coupling (increased Tc, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers

Highly Efficient Ag₂O/Bi₂O₂CO₃ p‑n Heterojunction Photocatalysts with Improved Visible-Light Responsive Activity

Ag₂O/Bi₂O₂CO₃ p-n heterojunctions are prepared with commercial Bi₂O₂CO₃ as precursor via a simple photosynthesis process. The obtained Ag₂O/Bi₂O₂CO₃ p-n heterojunctions show higher photocatalytic activity than that of pure n-Bi₂O₂CO₃, and the obtained Ag₂O/Bi₂O₂CO₃ (AB-4) heterojunction exhibits the best photocatalytic activity under visible light (λ > 400 nm), with which Rhodamine B, methyl blue and methyl orange can be completely degraded within 12 min. Photoluminescent spectra and photoelectrochemical measurement further indicate that the Ag₂O/Bi₂O₂CO₃ p-n heterojunctions greatly enhance the charge generation and suppress the charge recombination of photogenerated electron–hole pairs, which would be beneficial to improve their photocatalytic activity

Is La₃Ni₂O_6.5 a Bulk Superconducting Nickelate?

Superconducting states onsetting at moderately high temperatures have been observed in epitaxially stabilized RENiO2-based thin films. However, recently, it has also been reported that superconductivity at high temperatures is observed in bulk La3Ni2O7‑δ at high pressure, opening further possibilities for study. Here we report the reduction profile of La3Ni2O7 in a stream of 5% H2/Ar gas and the isolation of the metastable intermediate phase La3Ni2O6.45, which is based on Ni2+. Although this reduced phase does not superconduct at ambient or high pressures, it offers insights into the Ni-327 system and encourages future study of nickelates as a function of oxygen content

Nb Doping and Alloying of 2D WS₂ by Atomic Layer Deposition for 2D Transition Metal Dichalcogenide Transistors and HER Electrocatalysts

We utilize plasma-enhanced atomic layer deposition to synthesize two-dimensional Nb-doped WS2 and NbxW1–xSy alloys to expand the range of properties and improve the performance of 2D transition metal dichalcogenides for electronics and catalysis. Using a supercycle deposition process, films are prepared with compositions spanning the range from WS2 to NbS3. While the W-rich films form crystalline disulfides, the Nb-rich films form amorphous trisulfides. Through tuning the composition of the films, the electrical resistivity is reduced by 4 orders of magnitude compared to pure ALD-grown WS2. To produce Nb-doped WS2 films, we developed a separate ABC-type supercycle process in which a W precursor pulse precedes the Nb precursor pulse, thereby reducing the minimum Nb content of the film by a factor of 3 while maintaining a uniform distribution of the Nb dopant. Initial results are presented on the electrical and electrocatalytic performances of the films. Promisingly, the NbxW1–xSy films of 10 nm thickness and composition x ≈ 0.08 are p-type semiconductors and have a low contact resistivity of (8 ± 1) × 102 Ω cm to Pd/Au contacts, demonstrating their potential use in contact engineering of 2D TMD transistors

Modularly Constructed Polyhedral Oligomeric Silsesquioxane-Based Giant Molecules for Unconventional Nanostructure Fabrication

Controlled assembly of nanoscale building blocks is a promising approach to obtain functional materials with unique properties. Here, we report a way to manipulate the supramolecular structures of giant molecules based on discotic triangle cores and isobutyl polyhedral oligomeric silsesquioxanes (BPOSS) nanoparticles (NPs). It is found that depending upon the number of BPOSS at the periphery of the discotic cores, the packing of these nanoscale components (discotic core and POSS) could be manipulated into either cylindrical or Frank–Kasper (F–K) A15 (Pm3̅n) phases. The formation of these supramolecular nanostructures is mandated by the balance between the stacking of the discotic cores and the steric hindrance effect of the BPOSS NPs. This strategy to manipulate the packing of nanoscale building blocks for different supramolecular nanostructures including the fabrication of cylindrical structures and A15 (Pm3̅n) phases may be extended to other nanoscale building blocks for future development of materials with complex structures as well as tailored functionalities and properties

Hidden Hydroxides in KOH-Grown BaNiO₃ Crystals: A Potential Link to Their Catalytic Behavior

The hexagonal perovskite BaNiO3, prepared via nonceramic approaches, is known to act as a good catalyst for the oxygen evolution reaction (OER) in alkaline media. Here, we report our observation that BaNiO3 synthesized via KOH flux growth and high-pressure ceramic synthesis with high O2 pressure have different magnetic properties. We show that this is because the KOH flux-grown crystals made in open air are actually a hydroxide-containing form of BaNiO3 that can be “dried” upon annealing in an O2 flow. This work not only unveils a previously unknown aspect of the BaNiO3 OER catalyst and offers some insights into the underlying mechanism, but also suggests that hydroxide ions may be present in other hexagonal perovskite oxides prepared in wet conditions