CHROMIUM IMPURITIES IN INCIPIENT FERROELECTRIC KTAO3

The first observation of chromium impurities centres in single crystal s of KTaO3 by the ESR method is reported. The spectra of two types of chromium ions were observed in different samples: Cr5+ and Cr+ substit uted for Ta5+ and K+, respectively. The Cr5+ spectrum at T = 290 K has been described by an isotropic g-factor of g = 1.950(2). The manifest ation of a dynamic Jahn-Teller effect in the observed spectrum as well as the possibility of a static Jahn-Teller effect in the Cr5+ ESR spe ctrum at low temperatures are discussed. The ESR spectrum of Cr+ was d escribed by a spin-hamiltonian of cubic symmetry with the following pa rameters: g = 1.997(2), b(4)(0) = 171(2) x 10(-4) cm(-1) and b(4)(4) = 830(15) x 10(-4) cm(-1) at T = 77 K. The large width of fine lines of this spectrum and the width angular dependence were explained on the basis of Cr+ random off-center displacements in the [001] directions. The ESR spectrum of Cr3+ was not observed at T greater than or equal t o 77 K in all KTaO3 samples doped by chromium. The possible reasons of the Cr3+ ESR silence in KTaO3:Cr are discussed. Copyright (C) 1996 Pu blished by Elsevier Science Ltd