The Systematic Study on the Stability and Superconductivity of Y‐Mg‐H Compounds under High Pressure

First-principles investigation of the phase diagram and superconducting properties of the Sc-Mg-H system under high pressure

Superconductors, known for their zero electrical resistance and perfect diamagnetism, hold great promise for broad applications. In this study, we employed particle swarm optimization combined with first-principles calculations to predict the structures of Sc-Mg-H compounds under elevated pressure. Our approach identified four stable configurations within the pressure range of 30 to 250 GPa: ScMgH8-P4/mmm (stable from 30 to 250 GPa), ScMgH12-Cmmm (stable from 80 to 250 GPa), Sc2MgH18-P3̄m1 (stable from 110 to 250 GPa), and ScMg2H18-P3̄m1 (stable from 200 to 250 GPa). Through enthalpy calculations, we constructed the pressure-composition phase diagram of the Sc-Mg-H system and explored the stability and superconductivity of these compounds. The superconducting transition temperature (Tc) of Sc2MgH18 reaches 112 K at 150 GPa, ScMgH8 (at 80 GPa) and ScMgH12 (at 100 GPa) have Tc values of 56 K and 87 K, respectively. As the hydrogen content increases, ScMg2H18 requires the highest stabilizing pressure of 200 GPa and has a Tc of 98 K. These findings offer valuable insights for future high-temperature superconductor research and provide theoretical guidance for synthesizing novel materials with superior properties.

Prediction of potential high-temperature superconductivity in ternary Y-Hf-H compounds under high pressure

Compressed ternary alloy superhydrides are currently considered to be the most promising competitors for high-temperature superconducting materials. Here, the stable stoichiometries in the Y-Hf-H ternary system under pressure are comprehensively explored in theory and four fresh phases are predicted: Pmna-YHfH6 and P4/mmm-YHfH7 at 200 GPa, P4/mmm-YHfH8 at 300 GPa and P-6m2-YHfH18 at 400 GPa. The four Y-Hf-H ternary phases are thermodynamically and dynamically stable at corresponding pressure. In addition, structural features, bonding characteristics, electronic properties, and superconductivity of the four ternary Y-Hf-H phases are systematically calculated and discussed. As the hydrogen content and the density of states of H atoms at the Fermi level increase, the superconducting transition temperatures (Tc) of Y-Hf-H system are significantly enhanced. The P-6m2-YHfH18 with high hydrogen content exhibits a high calculated Tc value of 130 K at 400 GPa.

Clathrate metal superhydrides under high-pressure conditions: enroute to room-temperature superconductivity

Room-temperature superconductivity has been a long-held dream of mankind and a focus of considerable interest in the research field of superconductivity. Significant progress has recently been achieved in hydrogen-based superconductors found in superhydrides (hydrides with unexpectedly high hydrogen contents) that are stabilized under high-pressure conditions and are not capturable at ambient conditions. Of particular interest is the discovery of a class of best-ever-known superconductors in clathrate metal superhydrides that hold the record for high superconductivity (e.g. T c = 250-260 K for LaH10) among known superconductors and have great promise to be those that realize the long-sought room-temperature superconductivity. In these peculiar clathrate superhydrides, hydrogen forms unusual 'clathrate' cages containing encaged metal atoms, of which such a kind was first reported in a calcium hexa-superhydride (CaH6) showing a measured high T c of 215 K under a pressure of 170 GPa. In this review, we aim to offer an overview of the current status of research progress on the clathrate metal superhydride superconductors, discuss the superconducting mechanism and highlight the key features (e.g. structure motifs, bonding features, electronic structure, etc.) that govern the high-temperature superconductivity. Future research direction along this line to find room-temperature superconductors will be discussed.

Superconducting ternary hydrides: progress and challenges

Since the discovery of the high-temperature superconductors H3S and LaH10 under high pressure, compressed hydrides have received extensive attention as promising candidates for room-temperature superconductors. As a result of current high-pressure theoretical and experimental studies, it is now known that almost all the binary hydrides with a high superconducting transition temperature (T c) require extremely high pressure to remain stable, hindering any practical application. In order to further lower the stable pressure and improve superconductivity, researchers have started exploring ternary hydrides and had many achievements in recent years. Here, we discuss recent progress in ternary hydrides, aiming to deepen the understanding of the key factors regulating the structural stability and superconductivity of ternary hydrides, such as structural motifs, bonding features, electronic structures, electron-phonon coupling, etc. Furthermore, the current issues and challenges of superconducting ternary hydrides are presented, together with the prospects and opportunities for future research.

Strategies for improving the superconductivity of hydrides under high pressure

The successful prediction and confirmation of unprecedentedly high-temperature superconductivity in compressed hydrogen-rich hydrides signify a remarkable advancement in the continuous quest for attaining room-temperature superconductivity. The recent studies have established a broad scope for developing binary and ternary hydrides and illustrated correlation between specific hydrogen motifs and high-Tcs under high pressures. The analysis of the microscopic mechanism of superconductivity in hydrides suggests that the high electronic density of states at the Fermi level (EF), the large phonon energy scale of the vibration modes and the resulting enhanced electron-phonon coupling are crucial contributors towards the high-Tcphonon-mediated superconductors. The aim of our efforts is to tackle forthcoming challenges associated with elevating theTcand reducing the stabilization pressures of hydrogen-based superconductors, and offer insights for the future discoveries of room-temperature superconductors. Our present Review offers an overview and analysis of the latest advancements in predicting and experimentally synthesizing various crystal structures, while also exploring strategies to enhance the superconductivity and reducing their stabilization pressures of hydrogen-rich hydrides.

A systematic study on the phase diagram and superconductivity of ternary clathrate Ca-Sc-H at high pressures

This work explores potential high-temperature superconductor materials in hydrogen-rich systems. Here, the crystal structure stabilities of ternary Ca-Sc-H systems under high-pressure (P = 100-250 GPa) and their superconductivities are investigated using the particle swarm optimization methodology combined with first-principles calculations. For the predicted candidate structures of Ca-Sc-H systems, the pressure-dependent phase diagram and thermodynamic convex hull were investigated across a wide range of compositions; the electronic properties of all the predicted phases were analyzed in detail to study the bonding behavior of these stable phases. We identified the crystal structures of four thermodynamically stable compounds: R3̄m-CaScH6, Immm-CaSc2H9,C2/m-Ca2ScH10, and R3̄m-CaScH12. Among them, R3̄m-CaScH12 was predicted to have the highest Tc value (i.e., 173 K) at 200 GPa. The discovery of this previously unreported pressure-induced decomposition of Ca-Sc-H systems will pave the way for investigations on the nature of hydrogen-metal interactions.

Prediction for high superconducting ternary hydrides below megabar pressure

The recent findings of high-temperature hydrides ushered a new era of superconductivity research under high pressure. However, the stable pressure for these remarkable hydrides remains extremely high. In this work, we performed the extensive simulations on a series of hydrides with the prototype structure of UH₈and UH₇. Our results indicate several compounds possess superconducting critical temperature (T_c) above liquid nitrogen temperature below 100 GPa, such as CeBeH₈and ThBeH₈that are dynamical stable with aT_cof 201 K at 30 GPa and aT_cof 98 K at 10 GPa, respectively. Further formation enthalpy calculations suggest that thermodynamical stable pressure of CeBeH₈and ThBeH₈compounds is above 50 GPa and 88 GPa with respect to binary compounds and solid elements. Moreover, we also found that ThBeH₇could be dynamically stable down to 20 GPa with aT_cof 70 K. Our further simulations suggested this newly predicted ThBeH₇is thermodynamically stable above pressure of 33 GPa with respect to binary compounds and solid elements. The present results shed light on future design and discovery of high-temperature superconductor at moderate pressure.