Pressure-induced spin transition and site-selective metallization in CoCl2

Abstract

The interplay between spin states and metallization in compressed CoCl2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio calculations. A pressure-induced metallization along with a Co2+ high-spin (S\u2009=\u20093/2) to low-spin (S\u2009=\u20091/2) crossover transition is observed at high pressure near 70\u2009GPa. This metallization process, which is associated with the p-d charge-transfer band gap closure, maintains the localization of\xa03d electrons around Co2+, demonstrating that metallization and localized Co2+ -3d low-spin magnetism can coexist prior to the full 3d-electron delocalization (Mott-Hubbard d-d breakdown) at pressures greater than 180\u2009GPa.