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Variation of the Jahn–Teller distortion with pressure in the layered perovskite Rb2CuCl4: local and crystal compressibilities

This work investigates the effect of pressure on the Jahn–Teller distortion (JTD) associated with the axially elongated CuCl6 octahedra in the A2CuCl4 perovskite layer (A: Rb, CH3NH3, C2H5NH3, C3H7NH3). The aim is to elucidate whether pressure favours disappearance of the JTD in the antiferrodistortive (AFD) structure exhibited by Cu2+ within the layers or whether it induces tilts of the CuCl6 octahedra preserving the molecular distortion associated with the JT effect. We have carried out x-ray absorption (XAS) and x-ray diffraction (XRD) experiments under pressure along the compound series, whose interlayer distances at ambient pressure vary from 7.77 to 12.33 Å. The use of both XAS and XRD techniques allows us a complete local- and crystal-structure characterization in Rb2CuCl4 as a function of pressure in the 0–16 GPa range. We show that pressure reduces the axial (long) and equatorial (short) Cu–Cl distances, Rax and Req, as well as the intralayer and interlayer Cu–Cu distances, dCu−Cu and dinter. Interestingly, the variation of Rax is an order of magnitude bigger than that of the corresponding Req, yielding a reduction of the JTD. However, no evidence of JTD suppression has been observed below 16 GPa. Pressure-induced CuCl6 tilting preserves the JTD in a wide pressure range. Estimates based on structural data suggest that JT suppression would occur at about 40 GPa.