Adiabatic potential energy surface of the Jahn-Teller complexes in SrF2:Cr2+ crystal

Abstract

In SrF2 crystal doped with Cr 2+ ions, attenuation of all the normal ultrasonic modes with the wave vector k < 110 > were investigated at 52-162 MHz in the temperature region of 4-180 K. The observed peaks of relaxation origin were interpreted as manifestation of the Jahn-Teller effect.

Manifestation of the Jahn–Teller effect subject to quadratic T⊗e+t2 problem in ultrasonic attenuation. Case study of CaF2:Cr crystal with isovalent and aliovalent substitution

“…The second problem is in determining the background attenuation α b β entering the expression for α JT β given by equation (A.3). In CaF 2 :Ni 2+ [55] and SrF 2 :Cr 2+ [37,56], the measured attenuation α β reached its constant value at low temperatures in contrast with the studied CaF 2 :Cr. This circumstance made it possible to simulate α b β (T) for CaF 2 :Ni 2+ and SrF 2 :Cr 2+ as a monotonic function which coincides with α β (T ) at low temperatures and asymptotically approaches to it at T T 1 .…”

“…These barriers, as it was ascertained in our study, are much lower for CaF 2 :Cr 2+ . They can be roughly estimated by the values of the activation energy: V 0 = 132 K (CaF 2 :Cr 2+ ), V 0 = 380 K (SrF 2 :Cr 2+ [56]), and V 0 = 570 K (CaF 2 :Ni 2+ [55]). Consequently, the introduced method of τ (T ) construction can be used in future for investigation other JT sub-systems with low potential energy barriers and/or one more JT sub-system with overlapping anomalies in ultrasonic attenuation.…”