POLAR CENTERS AND UNUSUAL PROPERTIES OF MANGANITES WITH NONISOVALENT SUBSTITUTION

We introduce briefly the principal ideas of a new model approach to th e rare-earth manganites like LaMnO3 as to systems where the nonisovale nt substitution promotes the local disproportionation reaction with th e formation of the pseudo-Jahn-Teller (PJT)-centers phase being a syst em of the local triplet bosons moving in a lattice of the PJT-centers [MnO68-](JT). This situation is similar to that of the cuprates like Y Ba2Cu3O6+x, La2-xSrxCuO4, La2CuO4+delta or nickellites like La2NiO4+de lta. The unconventional properties of the substituted manganites like La1-xSrxMnO3 are connected with an active interplay of the charge, spi n, orbital and local structural (PJT-) modes with taking account of th e strong charge inhomogeneity; multi-granularity, static and dynamic p hase separation and percolation phenomena. (C) 1998 Elsevier Science B .V. All rights reserved.