On the pressure-induced spin transition in CoCl2. interplay between Jahn-Teller effect and spin sate in Co2+

Abstract

This work investigates on the interplay between the Jahn-Teller effect and spin state in Co2+(3d7 configuration). High-pressure optical absorption experiments were carried out in the 0 - 50 GPa range in CoCl2. This system is attractive since pressure increases the crystal-field splitting between eg and t2g levels from 0.9 eV to 1.6 eV, thus approaching CoCl2 towards the high-spin-to-low-spin transition. The free energy associated with the two states is discussed in terms of crystal-field and stabilization energies due to lattice relaxation including the Jahn-Teller effect, which is expected to be particularly strong in the low-spin configuration ( 2E;t2g6eg1) with respect to the weakly Jahn-Teller high-spin configuration (4T1; t2g5eg 2). The metallization process observed above 40 GPa is discussed in terms of spin transition and charge-transfer states. © 2008 IOP Publishing Ltd.