Harvesting PdH Employing Pd Nano Icosahedrons via High Pressure.

Palladium hydrides (PdHx ) have important applications in hydrogen storage, catalysis, and superconductivity. Because of the unique electron subshell structure of Pd, quenching PdHx materials with more than 0.706 hydrogen stoichiometry remains challenging. Here, the 1:1 stoichiometric PdH ( F m 3 ¯ m ) $Fm\bar{3}m)$ is successfully synthesized using Pd nano icosahedrons as a starting material via high-pressure cold-forging at 0.2 GPa. The synthetic initial pressure is reduced by at least one order of magnitude relative to the bulk Pd precursors. Furthermore, PdH is quenched at ambient conditions after being laser heated ≈2000 K under ≈30 GPa. Corresponding ab initio calculations demonstrate that the high potential barrier of the facets (111) restricts hydrogen atoms' diffusion, preventing hydrogen atoms from combining to generate H2 . This study paves the way for the high-pressure synthesis of metal hydrides with promising potential applications.

Structural diversity and hydrogen storage properties in the system K-Si-H.

KSiH3 exhibits 4.1 wt% experimental hydrogen storage capacity and shows reversibility under moderate conditions, which provides fresh impetus to the search for other complex hydrides in the K-Si-H system. Here, we reproduce the stable Fm3̄m phase of K2SiH6 and uncover two denser phases, space groups P3̄m1 and P63mc at ambient pressure, by means of first-principles structure searches. We note that P3̄m1-K2SiH6 has a high hydrogen content of 5.4 wt% and a volumetric density of 88.3 g L-1. Further calculations suggest a favorable dehydrogenation temperature Tdes of -20.1/55.8 °C with decomposition into KSi + K + H2. The higher hydrogen density and appropriate dehydrogenation temperature indicate that K2SiH6 is a promising hydrogen storage material, and our results provide helpful and clear guidance for further experimental studies. We found three further potential hydrogen storage materials stable at high pressure: K2SiH8, KSiH7 and KSiH8. These results suggest the need for further investigations into hydrogen storage materials among such ternary hydrides at high pressure.

Phase transitions and properties of lanthanum under high pressures.

Lanthanum (La), the first member of the lanthanide elements, recently aroused interests due to the discovery of high-Tcsuperconductor LaH10under high pressures and its unique superconducting properties. Here, we study the phase transitions, superconductivity and mechanical properties of metallic La under high pressures by first-principle calculations. The known face-centered cubic (fcc) phase with space groupFm3¯mstill exists above 100 GPa. And it transforms into an unprecedented body-centered tetragonal (bct) phase with space groupI4/mmmabove 180 GPa, which expands the high pressure phase transition sequence. Further calculations show that the superconducting transition temperatureTcof fcc phase decreases with increasing pressure with the rate of -0.13 K GPa-1, in good agreement with the experimental results. For the bct phase, the estimated superconducting transition temperature is very low withTcof 0.7 K at 200 GPa. The calculations of mechanical properties show that both of fcc and bct phases are compressible and brittle.

A novel differential display material: K3LuSi2O7: Tb3+/Bi3+ phosphor with thermal response, time resolution and luminescence color for optical anti-counterfeiting.

Optical anti-counterfeiting and encryption have become a hotspot in information security. However, the advanced optical anti-counterfeiting technology still suffers from low security by single-luminescent mode. Herein, we present a novel multi-mode anti-counterfeiting strategy based on K3LuSi2O7: Tb3+/Bi3+ (KLSO: Tb3+/Bi3+) phosphors for the first time. KLSO not only provides various lattice sites for Bi3+ ions occupying to achieve tunable luminescence but can also be non-equivalently substituted by Tb3+ ions to produce persistent or thermo-luminescence. Furthermore, in the pattern "8888" constructed by the mixture of polyacrylic acid (PAA) with KLSO: Tb3+/Bi3+ phosphors, we selectively trigger the three luminescent modes of Bi3+ and Tb3+ ions to realize the design of differential display in the fields of thermal response, time resolution, and luminescence color for optical anti-counterfeiting. The differentiated display can only be presented under specific multi-stimuli response, which further improves the security of information. Our work provides a new insight for designing advanced materials and can be expected to inspire future studies to explore optical anti-counterfeiting technology.

Pressure-Induced Superionicity of H- in Hypervalent Sodium Silicon Hydrides.

Superionic states simultaneously exhibit properties of a fluid and a solid. Proton (H+) superionicity in ice, H3O, He-H2O, and He-NH3 compounds is well-studied. However, hydride (H-) superionicity in H-rich compounds is rare, being associated with instability and strongly reducing conditions. Silicon, sodium, and hydrogen are abundant elements in many astrophysical bodies. Here, we use first-principles calculations to show that, at high pressure, Na, Si, and H can form several hypervalent compounds. A previously unreported superionic state of Na2SiH6 results from unconstrained H- in the hypervalent [SiH6]2- unit. Na2SiH6 is dynamically stable at low pressure (3 GPa), becoming superionic at 5 GPa, and re-entering solid/fluid states at about 25 GPa. Our observation of H- transport opens up a new field of H- conductors. It also has implications for the formation of conducting layers at depth in exotic carbon exoplanets, potentially enhancing the habitability of such planets.