PSEUDO-JAHN-TELLER-CENTERS AND PHASE-SEPARATION IN THE STRONGLY CORRELATED OXIDES WITH THE NONISOVALENT SUBSTITUTION - CUPRATES AND MANGANITES

We introduce briefly the principal ideas of a new model approach to th e strongly correlated oxides like cuprates (YBa2Cu3O6+x, La2-xSrxCuO4, La2CuO4+delta,...), manganites (La1-x,SrxMnO3,...), nickellates (La2N iO4+delta), bis-muthates ((K, Ba)BiO3) as systems where the nonisovale nt substitution promotes the local disproportionation reaction with th e formation of the polar (electron and hole) pseudo-Jahn-Teller (PJT) centers phase being a system of the local singlet or triplet bosons mo ving in a lattice of the hole PJT centers. The unconventional properti es of the substituted strongly correlated oxides are connected with an active interplay of the charge, spin, orbital and local structural (o r PJT) modes taking account of the strong charge inhomogeneity, multi- granularity, static and dynamic phase separation and percolation pheno mena. (C) 1998 Elsevier Science B.V. All rights reserved.