Abstract
The discovery of superconducting H3S with a critical temperature Tc∼200 K opened a door to room temperature superconductivity and stimulated further extensive studies of hydrogen-rich compounds stabilized by high pressure. Here, we report a comprehensive study of the yttrium-hydrogen system with the highest predicted Tcs among binary compounds and discuss the contradictions between different theoretical calculations and experimental data. We synthesized yttrium hydrides with the compositions of YH3, YH4, YH6 and YH9 in a diamond anvil cell and studied their crystal structures, electrical and magnetic transport properties, and isotopic effects. We found superconductivity in the Im-3m YH6 and P63/mmc YH9 phases with maximal Tcs of ∼220 K at 183 GPa and ∼243 K at 201 GPa, respectively. Fm-3m YH10 with the highest predicted Tc > 300 K was not observed in our experiments, and instead, YH9 was found to be the hydrogen-richest yttrium hydride in the studied pressure and temperature range up to record 410 GPa and 2250 K.
Highlights
In sample 28 at a lower pressure of 105 GPa, we found a new bcc phase with a composition close to YH4 (Supplementary Fig. 9b, c)
We did not find the fcc-YH10 phase despite extensive trials at pressures up to 410 GPa and temperatures up to 2250 K
Summary
X-ray diffraction data were collected at beamline 13-IDD at GSECARS, Advanced Photon Source, using λ1 = 0.2952 Å and λ2 = 0.3344 Å, a beam spot size of ~2.5 × 2.5 μm[2], and a Pilatus 1 M CdTe detector. To examine the formation of new yttrium hydrides at 325–410 GPa at high temperatures, we collected X-ray powder diffraction patterns in situ at high temperature. Each pattern was collected by accumulating 5 × 105 shots with a duration of 1 μs, which were synchronised with laser heating pulses. The temperature was determined by the thermal emission from the sample measured with a PI-MAX3 detector. Primary processing and integration of the powder patterns were performed using Dioptas software[57]. The indexing of powder patterns and refinement of the crystal structures were done with the GSAS and EXPGUI package
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