Abstract
Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressure-driven changes in electronic structures and insulator-to-metal transitions under high pressure.The λ-N2 formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far.By optimizing the optical system,we successfully measured the high-pressure absorption spectra of λ-N2 covering the polymeric-nitrogen synthetic pressures(124 GPa-165 GPa).The measured optical band gap decreases with increasing pres-sure,from 2.23eV at 124GPa to 1.55eV at 165GPa,with a negative pressure coefficient of-18.4meV/GPa,which is consistent with the result from our ab initio total-energy calculations(-22.6meV/GPa).The extrap-olative metallization pressure for the λ-N2 is around 288(18)GPa,which is close to the metallization pressure(280 GPa)for the 7-N2 expected by previous absorption edge and direct electrical measurements.Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.
基金项目
国家自然科学基金(12374013)
国家自然科学基金(U2030107)
国家自然科学基金(11974154)
中央高校基本科研业务费专项(2020SCUNL107)
Taishan Scholars Special Funding for Construction Projects()
万方数据