Eur. Phys. J. B 65, 187-190 (2008)
https://doi.org/10.1140/epjb/e2008-00338-y

Experimental estimation of the cooperative Jahn-Teller energy in orbitally ordered KCu_0.8Mg_0.2F₃ perovskite

¹ Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, V. Golgi 19, 20133 Milano, Italy
² European Synchrotron Radiation Facility, 6, av. J. Horowitz, BP 220, 38043 Grenoble Cedex, France
³ I.E.N.I.-C.N.R., and Dipartimento di Chimica Fisica, Università di Pavia, Viale Taramelli 16, 27100 Pavia, Italy

Corresponding author: ^a paolo.ghigna@unipv.it

Received: 25 February 2008
Revised: 22 July 2008
Published online: 5 September 2008

Abstract

High resolution synchrotron radiation X-ray powder diffraction was used to investigate the melting of the cooperative Jahn-Teller distortion (cJTd) in a perovskite of composition KCu_0.8Mg_0.2F₃. A first order phase transition relaxing the cJTd is observed at T ~ 600 K. From the transition temperature, an estimation of kT is derived (kT = 0.05 eV) for the cJTd in the doped compound. This is the very first observation of cJTd melting in a compound of the series KCuMg_xF₃. A structural phase diagram for the Cu rich zone of the series is proposed. In principle, the extension of this experimental investigation could be used to disentangle the orbital order (OO) and cJTd energy scales in the parent compound KCuF₃, a test system for OO theories.