MICROPHASE SEPARATION AND MAGNETIC JAHN-TELLER POLARONS IN LASRAL1-XCUXO4-DELTA

An EPR study of the solid solutions LaSrAl1-xCuxO4, which are isostruc tural to La2CuO4, shows that microphase separation of the structure oc curs already at small copper concentrations (x approximate to 0.01). A phase enriched with Cu appears along with a phase of La2AlO4, which c ontains isolated CuO6 centers. It is established that the nature of th e states and the deformations of the CuO6 centers is determined by int ernal Jahn-Teller factors. When x less than or equal to 0.1, EPR signa ls are detected for new dynamic centers, which are identified as CuO6 Jahn-Teller centers with a hole delocalized among the four in-plane ox ygen ions (the total spin S=1). When 0.1 less than or equal to x<1,loc al CuO6- hole centers transform into magnetic Jahn-Teller polarons, wh ich include five or more CuO6 fragments, in the copper phase of the st ructure. Their transformations and the conditions for observing them a re discussed. (C) 1998 American Institute of Physics.