Application of particle channeling to the study of a cooperative Jahn-teller phase transition in nickel chromite

Abstract

Development of particle channeling in single crystals has led to a number of important applications in studies of impurity ions in solids, crystal surface structures and decay of short-lived compound nuclei. In all of these cases the crucial property is the ability of channeled particles to distinguish spatial positions of crystal lattice atoms or impurity atoms with high accuracy. This property of channeled ions suggests potential application to studies of crystalline phase transitions, thermal motion of lattice atoms and investigation of the dynamic and static behavior of “off center” or Jahn-teller impurity ions. We report here on an experimental demonstration of these possibilities in a channeling study of a reversible cooperative Jahn-teller transition in nickel chromite. In these experiments the angular dependence of the normalized backscattering yields of 1.5 MeV helium ions from a NiCr 2O 4 single crystal close to the [111], [110], [11 1] , [211] and [12 1] crystallographic axes has been measured for va temperatures above and below and below the transition temperature. At the transition temperature an abrupt change in direction of the crystal axes was observed. In addition, the minimum yield of the channeling dips was found to change significantly.