Variation of the Jahn–Teller distortion with pressure in perovskite layers A₂CuCl₄. Influence on the charge‐transfer band

This work investigates the variation of the first charge‐transfer (CT) transition with pressure in the A 2 CuCl 4 layered perovskites, in terms of structural changes, in particular, the local structure of the (CuCl 6 ) 4– octahedra. We show that pressure partially reduces the Jahn–Teller distortion. The decrease of the axial Cu–Cl distance, R ax , is an order of magnitude bigger than the decrease of the equatorial distance, R eq , but the in‐plane Cu–Cu distance reduction is almost twice that the sum of R ax and R eq , thus indicating pressure‐induce tilts. This phenomenon avoids suppression of the JT effect, keeping the (CuCl 6 ) 4– axial distortion above 10 GPa. Both the partial reduction of the JT distortion and tiliting can account for the CT redshift induced by pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)