Polyhydrides with mysterious structures and detection of their superconductivity by radio-frequency methods
Dr. Dmitrii Semenok and Dr. Di Zhou
Center for High Pressure Science and Technology Advanced Research, Beijing, China
16:15 - 17:15 Tuesday 08 October 2024 TUG Pressure-stabilized hydrides are a new rapidly growing class of high-temperature superconductors. The remarkable properties of H$_3$S (T$_c$ = 200 K), YH$_6$ (T$_c$ = 224 K) and LaH$_{10}$ (T$_c$ = 250 K) at 130-200 GPa catalyzed the search for superconductivity in compressed ternary (X,Y)-H polyhydrides that can be obtained by pulsed laser heating of various alloys and intermetallics with hydrogen in diamond anvil cells. An important issue, affecting the applications of hydrides and the expansion of the number of research groups in this field, is the possibility of superhydrides synthesis at pressures below 60-65 GPa. Below this pressure, diamond anvils can be used several times, which significantly reduces the cost of experiments.
The report will be devoted to modern trends in the field of hydride chemistry and superconductivity under high pressure. I will talk about recent results related to superconductivity in Ba-Si-H, La-Sc-H and La-Ce-H ternary systems, including studies in strong pulsed magnetic fields up to 68 Tesla. X-ray diffraction data, transport measurements and magnetoresistance of these ternary hydrides will be discussed. Passage of radio frequency (RF) electromagnetic field, generated by microcoils, through a sample with nonlinear magnetic susceptibility is accompanied by the generation of higher harmonics of the input signal. It can be used to detect superconducting transitions in polyhydrides. I will show examples of detection of superconductivity in LaH$_{10-12}$ superhydrides and (La,Ce)H$_{10}$ at 148 GPa, as well as proof of concept of RF measurements using BSCCO piece of about 100 um size.
Ultrastable (< 10 GPa) polyhydrides that are promising for hydrogen storage. We experimentally investigated the formation of Cs and Rb hydrides in the process of laser heating their salts CsNH$_2$BH$_3$ and RbNH$_2$BH$_3$ under a pressure of 10-40 GPa [Zhou et al. Adv. Energy Mater, 2024, 2400077]. We observed powder XRD patterns from two phases of rubidium hydrides RbH$_{9-x}$ and cesium hydride CsH$_7$, theoretically predicted back in 2015-2017. Moreover, there are other polyhydrides in the system (for example, CsH$_{15-17}$), including pseudocubic RbH$_9$, (meta)stable below 8 GPa. Stabilization of such polyhydrides at low pressures can be achieved due to the presence of impurities in their lattice. We will also discuss unusually high stability of BaSiH$_8$, BaSiH$_7$, and some novel La polyhydrides (LaH$_{12}$).
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