Chromium impurities in incipient ferroelectric KTaO sub(3)

The first observation of chromium impurities centres in single crystals of KTaO sub(3) by the ESR method is reported. The spectra of two types of chromium ions were observed in different samples: Cr super(5+) and Cr super(+) substituted for Ta super(5+) and K super(+), respectively. The Cr super(5+) spectrum at T identical with 290 K has been described by an isotropic g-factor of g identical with 1.950(2). The manifestation of a dynamic Jahn-Teller effect in the observed spectrum as well as the possibility of a static Jahn-Teller effect in the Cr super(5+) ESR spectrum at low temperatures are discussed. The ESR spectrum of Cr super(+) was described by a spin-hamiltonian of cubic symmetry with the following parameters: g identical with 1.997(2), b super(0) sub(4) identical with 171(2) x 10 super(-4) cm super(-1) and b super(4) sub(4) identical with 830(15) x 10 super(-4) cm super(-1) at T identical with 77 K. The large width of fine lines of this spectrum and the width angular dependence were explained on the basis of Cr super(+) random off-center displacements in the [001] directions. The ESR spectrum of Cr super(3+) was not observed at T greater than or equal to 77 K in all KTaO sub(3) samples doped by chromium. The possible reasons of the Cr super(3+) ESR silence in KTaO sub(3):Cr are discussed.