RESUMEN
As compressed hydrides constantly refresh the records of superconducting critical temperatures (Tc) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P63/mmc-LaH10) stabilized at 146 GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with Tc â¼ 178 K, and this value is enhanced to a maximum Tc â¼ 223 K at 164 GPa. A huge upper critical magnetic field value Hc2(0) reaches 223 T at 146 GPa. The small volume expansion of P63/mmc-(La, Al) H10 compared with the binary LaH10 indicates the possible interstitial sites of Al atoms filling into the La-H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system.
RESUMEN
Ternary hydrides are regarded as an important platform for exploring high-temperature superconductivity at relatively low pressures. Here, we successfully synthesized the hcp-(La,Ce)H9-10 at 113 GPa with the initial La/Ce ratio close to 3:1. The high-temperature superconductivity was strikingly observed at 176 K and 100 GPa with the extrapolated upper critical field Hc2(0) reaching 235 T. We also studied the binary La-H system for comparison, which exhibited a Tc of 103 K at 78 GPa. The Tc and Hc2(0) of the La-Ce-H are respectively enhanced by over 80 K and 100 T with respect to the binary La-H and Ce-H components. The experimental results and theoretical calculations indicate that the formation of the solid solution contributes not only to enhanced stability but also to superior superconducting properties. These results show how better superconductors can be engineered in the new hydrides by large addition of alloy-forming elements.
RESUMEN
Recently, several research groups announced reaching the point of metallization of hydrogen above 400 GPa. Despite notable progress, detecting superconductivity in compressed hydrogen remains an unsolved problem. Following the mainstream of extensive investigations of compressed metal polyhydrides, here small doping of molecular hydrogen by strontium is demonstrated to lead to a dramatic reduction in the metallization pressure to ≈200 GPa. Studying the high-pressure chemistry of the Sr-H system, the formation of several new phases is observed: C2/m-Sr3 H13 , pseudocubic SrH6 , SrH9 with cubic F 4 ¯ 3 m $F\bar{4}3m$ -Sr sublattice, and pseudo tetragonal superionic P1-SrH22 , the metal hydride with the highest hydrogen content (96 at%) discovered so far. High diffusion coefficients of hydrogen in the latter phase DH = 0.2-2.1 × 10-9 m2 s-1 indicate an amorphous state of the H-sublattice, whereas the strontium sublattice remains solid. Unlike Ca and Y, strontium forms molecular semiconducting polyhydrides, whereas calcium and yttrium polyhydrides are high-TC superconductors with an atomic H sublattice. The discovered SrH22 , a kind of hydrogen sponge, opens a new class of materials with ultrahigh content of hydrogen.
RESUMEN
The discoveries of high-temperature superconductivity in H_{3}S and LaH_{10} have excited the search for superconductivity in compressed hydrides, finally leading to the first discovery of a room-temperature superconductor in a carbonaceous sulfur hydride. In contrast to rapidly expanding theoretical studies, high-pressure experiments on hydride superconductors are expensive and technically challenging. Here, we experimentally discovered superconductivity in two new phases, Fm3[over ¯]m-CeH_{10} (SC-I phase) and P6_{3}/mmc-CeH_{9} (SC-II phase) at pressures that are much lower (<100 GPa) than those needed to stabilize other polyhydride superconductors. Superconductivity was evidenced by a sharp drop of the electrical resistance to zero and decreased critical temperature in deuterated samples and in external magnetic field. SC-I has T_{c}=115 K at 95 GPa, showing an expected decrease in further compression due to the decrease of the electron-phonon coupling (EPC) coefficient λ (from 2.0 at 100 GPa to 0.8 at 200 GPa). SC-II has T_{c}=57 K at 88 GPa, rapidly increasing to a maximum T_{c}â¼100 K at 130 GPa, and then decreasing in further compression. According to the theoretical calculation, this is due to a maximum of λ at the phase transition from P6_{3}/mmc-CeH_{9} into a symmetry-broken modification C2/c-CeH_{9}. The pressure-temperature conditions of synthesis affect the actual hydrogen content and the actual value of T_{c}. Anomalously low pressures of stability of cerium superhydrides make them appealing for studies of superhydrides and for designing new superhydrides with stability at even lower pressures.
RESUMEN
Rare-earth (RE) superhydrides have great potential as high-temperature superconductors, with recent discoveries almost achieving room-temperature superconductivity in compressed LaH10 and YH9. Here, we continue to study the rare-earth hydrides by focusing on the new hydrides that the lightest element Sc and the heaviest element Lu formed under pressure. Two new superconducting hydrides ScH3 (Tc â¼ 18.5 K at 131 GPa) and LuH3 (Tc â¼ 12.4 K at 122 GPa) have been identified both with cubic structure by combining X-ray diffraction and electrical resistance techniques. Among all of the REH3, only the superconducting properties of ScH3 and LuH3 have been experimentally confirmed. Our current results may offer guidance to other REH3, which were predicted to be superconductors but have not been experimentally confirmed.
RESUMEN
Following the discovery of high-temperature superconductivity in the La-H system, we studied the formation of new chemical compounds in the barium-hydrogen system at pressures from 75 to 173 GPa. Using in situ generation of hydrogen from NH3BH3, we synthesized previously unknown superhydride BaH12 with a pseudocubic (fcc) Ba sublattice in four independent experiments. Density functional theory calculations indicate close agreement between the theoretical and experimental equations of state. In addition, we identified previously known P6/mmm-BaH2 and possibly BaH10 and BaH6 as impurities in the samples. Ab initio calculations show that newly discovered semimetallic BaH12 contains H2 and H3- molecular units and detached H12 chains which are formed as a result of a Peierls-type distortion of the cubic cage structure. Barium dodecahydride is a unique molecular hydride with metallic conductivity that demonstrates the superconducting transition around 20 K at 140 GPa.
RESUMEN
We conducted a joint experimental-theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86-130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic EuH9, hexagonal EuH9, and an unexpected cubic (Pm3n) clathrate phase, Eu8H46. Monte Carlo simulations indicate that cubic EuH9 has antiferromagnetic ordering with TN of up to 24 K, whereas hexagonal EuH9 and Pm3n-Eu8H46 possess ferromagnetic ordering with TC = 137 and 336 K, respectively. The electron-phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes s-wave superconductivity, except, perhaps, for distorted pseudohexagonal EuH9. The equations of state predicted within the DFT+U approach (U - J were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.
RESUMEN
Superhydrides have complex hydrogenic sublattices and are important prototypes for studying metallic hydrogen and high-temperature superconductors. Previous results for LaH10 suggest that the Pr-H system may be especially worth studying because of the magnetism and valence-band f-electrons in the element Pr. Here, we successfully synthesized praseodymium superhydrides (PrH9) in laser-heated diamond anvil cells. Synchrotron x-ray diffraction analysis demonstrated the presence of previously predicted F 4 ¯ 3m-PrH9 and unexpected P63/mmc-PrH9 phases. Experimental studies of electrical resistance in the PrH9 sample showed the emergence of a possible superconducting transition (T c) below 9 K and T c dependent on the applied magnetic field. Theoretical calculations indicate that magnetic order and likely superconductivity coexist in a narrow range of pressures in the PrH9 sample, which may contribute to its low superconducting temperature. Our results highlight the intimate connections between hydrogenic sublattices, density of states, magnetism, and superconductivity in Pr-based superhydrides.
RESUMEN
Hybrid organic-inorganic perovskites (HOIPs) have gained substantial attention due to their excellent photovoltaic and optoelectronic properties. Herein, we comprehensively investigate a typical two-dimensional (2D) hybrid perovskite (C6H5CH2NH3)2PbI4 to track its structural and band gap evolution applied by the maximum pressure of 27.2 GPa. Remarkably, an unprecedented band gap narrowing down to the Shockley-Queisser limit is observed upon compression to 20.1 GPa. Two phase transitions have been observed during this process: the ambient Pbca phase converts into the Pccn phase at 4.6 GPa and then undergoes an isostructural phase transition at 7.7 GPa. The Fourier Transform Infrared (FTIR) spectroscopy reveals that pressure-enhanced hydrogen bonding plays an important role in structural modifications and band gap variations. This work not only enables high pressure as a clean tool to tune the structure and band gap of hybrid perovskite, but also maps a pioneering route towards realizing ideal photovoltaic materials-by-design.
