Fig. 1. Transport measurements for the sample obtained at 65 °C at low temperature and high pressure. (a)–(c) Temperature dependence of resistance measured in the pressure range 0.9–3.4 GPa. The insets show the arrangements of the sample and the standard four probes; the sample is indicated by the red dashed box. (d)–(f) Magnetic susceptibility vs temperature measured in the pressure range 0.8–3.3 GPa and temperature range 100–300 K. The data were obtained with background subtraction. The inset in (d) shows the sample in a gasket hole. Our resistance and magnetic results demonstrate that there is no evidence of superconductivity in the sample.

Fig. 2. XRD analysis of the sample obtained at 65 °C. All the diffraction peaks can be assigned to the FCC-1 phase (Fm-3m) with lattice parameter a = 5.03 Å (red bars), the FCC-2 phase (Fm-3m) with lattice parameter a = 4.755 Å (green bars), and the Lu metal (blue bars).

Fig. 3. Scanning electron microscopy (SEM) image and EDS analysis of the sample obtained at 65 °C. (a) SEM image taken from the produced sample surface. Eleven locations (marked by crosses) were selected to collect the EDS. (b) The overlay of the 11 EDS spectra measured shows that no nitrogen is incorporated in the sample.

Fig. 4. Transport property and structural characterizations on the sample obtained at 1800 °C. (a) Temperature dependence of resistance measured at different pressures, displaying no evidence of superconductivity in the experimental range of 0.9–6.5 GPa. (b) and (c) Photographs taken at 2.8 and 6.5 GPa, demonstrating that the sample’s color remains dark blue. (c) XRD pattern from the produced sample, revealing the presence of three substances: LuH₂ (red bars), FCC-2 phase (Fm-3m, green bars) and LuH₃ (blue bars).