Fig. 1. In situ electric resistance measurements of the Lu foil sample loaded with H₂/N₂ gas mixture in a DAC at 10 GPa and 295 K. The insets present optical micrographs of the Lu foil sample as loaded (left) and after a 5-day reaction (right), showing the four Pt electrodes. The metallic luster of the surface of the Lu foil sample changes to dark blue after 5 days of reaction. The colorful fringes are due to light interference between the gap from the sample to the diamond-anvil surface, which becomes invisible after reaction mainly due to much less light being reflected by the dark sample surface. The obvious consumption of H₂/N₂ gas mixture was reflected by sample-chamber shrinkage after 5 days of reaction. The sample size also slightly increased after the reaction. The blue and red curves show the temperature-dependent raw resistance values during warming from 2 K (10 K) to 300 K for the initial pure Lu metal before reaction and the same sample after reacting for 5 days at 10 GPa and 295 K, respectively.