Ultrafast Yttrium Hydride Chemistry at High Pressures via Non-equilibrium States Induced by an X-ray Free Electron Laser.

Controlling the formation and stoichiometric content of the desired phases of materials has become of central interest for a variety of fields. The possibility of accessing metastable states by initiating reactions by X-ray-triggered mechanisms over ultrashort time scales has been enabled by the development of X-ray free electron lasers (XFELs). Utilizing the exceptionally high-brilliance X-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with nonstoichiometric changes in hydrogen content as probed at a repetition rate of 4.

Retraction: Synthesis of Yttrium Superhydride Superconductor with a Transition Temperature up to 262 K by Catalytic Hydrogenation at High Pressures [Phys. Rev. Lett. 126, 117003 (2021)].

Retraction of DOI: 10.1103/PhysRevLett.126.

Retraction: Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa.

Retraction of 'Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa' by G. Alexander Smith , , 2022, , 9064-9067, https://doi.org/10.

Expression of Concern: Synthesis of Yttrium Superhydride Superconductor with a Transition Temperature up to 262 K by Catalytic Hydrogenation at High Pressures [Phys. Rev. Lett. 126, 117003 (2021)].

This corrects the article DOI: 10.1103/PhysRevLett.126.

High-Pressure Synthesis of a High-Pressure Phase of MnN Having NiAs-Type Structure.

A novel high-pressure phase of manganese mononitride, NiAs-type MnN, was successfully synthesized through a pressure-induced phase transition from a tetragonal distorted NaCl-type MnN at pressures above approximately 55 GPa. High-pressure experiments, including starting material preparation, were conducted using a laser-heated diamond anvil cell. This result is the first example of a nitride with a structural phase transition from the distorted NaCl-type to the NiAs-type structure.

Retraction: Colossal Density-Driven Resistance Response in the Negative Charge Transfer Insulator MnS_{2} [Phys. Rev. Lett. 127, 016401 (2021)].

Retraction of DOI: 10.1103/PhysRevLett.127.

Stable and metastable structures of tin (IV) oxide at high pressure.

We have analysed [Formula: see text] with a combination of synchrotron X-ray diffraction and X-ray absorption spectroscopy across a pressure range of [Formula: see text] GPa with thermal annealing by a [Formula: see text] laser allowing access to all of the known high-density polymorphs of [Formula: see text], and here report their crystallographic information. The metastability of the post-rutile [Formula: see text]-[Formula: see text] and [Formula: see text] structures in [Formula: see text] are investigated by experiment and PW-DFT simulations, revealing a complex energetic landscape and suggesting a significant dependence of the observed phases on the pressure-temperature pathway taken in experiment. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Evidence of near-ambient superconductivity in a N-doped lutetium hydride.

The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized. At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures (T), up to about 133 K (refs.

Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa.

We report a previously unobserved superconducting state of the photosynthesized carbonaceous sulfur hydride (C-S-H) system with a maximum of 191(1) K below 100 GPa. The properties of C-S-H are dependent on carbon content, and X-ray diffraction and simulations reveal the system remains molecular-like up to 100 GPa.

Pressure-induced metallization and 3d-like behavior in TcS.

TcS undergoes a charge transfer insulator to metal transition above 28 GPa. Laser annealing reveals a kinetically hindered high pressure arsenopyrite phase that is recoverable to ambient. The new phase is similar to the Mn-dichalcogenides rather than the expected Re-dichalcogenides and involves the formation of S-S and Tc-Tc bonds.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods.

Synthesis and chemical stability of technetium nitrides.

We demonstrate the synthesis and phase stability of TcN, TcN, and a substoichiometric TcN from 0 to 50 GPa and to 2500 K in a laser-heated diamond anvil cell. At least potential recoverability is demonstrated for each compound. TcN adopts a previously unpredicted structure identified via crystal structure prediction.

Colossal Density-Driven Resistance Response in the Negative Charge Transfer Insulator MnS_{2}.

A reversible density driven insulator to metal to insulator transition in high-spin MnS_{2} is experimentally observed, leading with a colossal electrical resistance drop of 10^{8}  Ω by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied S_{2}^{2-} σ_{3p}^{*} antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence.

A 70-Year-Old Mystery in Technetium Chemistry Explained by the New Technetium Polyoxometalate [H O ] [Tc O ] ⋅ 4H O.

[H O ] [Tc O ] ⋅ 4H O [1] was prepared from an aqueous Tc O solution concentrated over anhydrous H SO . [Tc O ] is the first polyanionic species to be reported for Tc. The unit cell contains one centrosymmetric [Tc O ] polyanion as well as hydronium ions and water molecules.

Synthesis of Yttrium Superhydride Superconductor with a Transition Temperature up to 262 K by Catalytic Hydrogenation at High Pressures.

The recent observation of room-temperature superconductivity will undoubtedly lead to a surge in the discovery of new, dense, hydrogen-rich materials. The rare earth metal superhydrides are predicted to have very high-T_{c} superconductivity that is tunable with changes in stoichiometry or doping. Here we report the synthesis of an yttrium superhydride that exhibits superconductivity at a critical temperature of 262 K at 182±8  GPa.

Decoupling Lattice and Magnetic Instabilities in Frustrated CuMnO.

The AMnO delafossites (A = Na, Cu) are model frustrated antiferromagnets, with triangular layers of Mn spins. At low temperatures ( = 65 K), a 2/ → 1̅ transition is found in CuMnO, which breaks frustration and establishes magnetic order. In contrast to this clean transition, A = Na only shows short-range distortions at .

Coexistence of metamagnetism and slow relaxation of magnetization in ammonium hexafluoridorhenate.

The (NH)[ReF] (1) salt was studied by X-ray diffraction, Raman spectroscopy, theoretical calculations, and magnetic measurements. 1 crystallizes in the trigonal space group 3̄1 (Re-F = 1.958(5) Å).

Publisher Correction: Room-temperature superconductivity in a carbonaceous sulfur hydride.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Room-temperature superconductivity in a carbonaceous sulfur hydride.

One of the long-standing challenges in experimental physics is the observation of room-temperature superconductivity. Recently, high-temperature conventional superconductivity in hydrogen-rich materials has been reported in several systems under high pressure. An  important discovery leading to room-temperature superconductivity is the pressure-driven disproportionation of hydrogen sulfide (HS) to HS, with a confirmed transition temperature of 203 kelvin at 155 gigapascals.

Anomalous Conductivity in the Rutile Structure Driven by Local Disorder.

Many rutile-type materials are characterized by a softness in shear with pressure which is coupled to a Raman-active librational motion. Combining direct studies of anion positions in SnO with measurements of its electronic properties, we find a correlation between O sublattice disorder between 5 and 10 GPa and an anomalous decrease up to 4 orders of magnitude in electrical resistance. Hypotheses into the atomistic nature of the phenomenon are evaluated via ab initio calculations guided by extended X-ray absorption fine structure spectroscopy analysis, and the most likely mechanism is found to be the displacement of single anions resulting from the pressure-induced softening of the librational mode.

The purported square ice in bilayer graphene is a nanoscale, monolayer object.

The phase diagram of water is complex, and interfacial effects can stabilize unusual structures at the nanoscale. Here, we employ bond order accelerated molecular dynamics simulations to show that upon encapsulation within bilayer graphene, water can spontaneously adopt a two-dimensional (monomolecular) layer of "square ice" at ambient conditions, instead of an encapsulated water droplet. Free energy calculations show that this motif is thermodynamically stable up to diameters of approximately 15 nm due to enhanced hydrogen bonding and favorable binding to the graphene sheets.

Covalency is Frustrating: LaSnO and the Nature of Bonding in Pyrochlores under High Pressure-Temperature Conditions.

Natural specimens of the pyrochlore (ABO) compounds have been found to retain foreign actinide impurities within their parent framework, undergoing metamictization to a fully amorphous state. The response to radionuclide decay identifies pyrochlore systems with having high radiation tolerance and tailored use in radioactive waste applications and radionuclide sequestration. High pressure is a powerful pathway to high density states and amorphization with parallels to radiation-induced processes.