Channeling study of the co-operative Jahn-Teller effect in nickel chromite single crystal by backscattering and resonant nuclear scattering of helium ions

Using the channeling technique, the co-operative Jahn-Teller effect in nickel chromite single crystals has been studied by helium ion backscattering and the resonant nuclear scattering of O16(α, α)O16 at Esub(α)=3.056 MeV. The results have shown that the channeling dips for Ni+Cr and O atoms around <110>, <111> and [11anti 1] axes become shallow at temperatures below the dynamic to static Jahn-Teller transition, which has been attributed to extra dechanneling due to the domain effect and explained by the (110) twin model. Also there is some indication that the Ni or Cr atoms (or both) are laterally displaced from the <111> or <11anti 1> axis at tempeatures lower than the transition temperature. This differs from the usual expectation for the co-operative Jahn-Teller effect. (orig.)