EPR of Cu²⁺ and radiation centres in anatase (TiO₂)

Abstract

The EPR spectra of three different CuZ+ centres and the spectrum of the radiation hole centre i n single cryst,als of anatase are investigated. The constants of the spin-Hamiltonians for all the spectra and the ground state wave functions are obtained. The conditions of incorporation into the crystal, the site of impurity in the lattice, and the mechanism of charge compensation are discussed. k3CCJIenOBaHM CneKTpbI 3nP TpeX pa3JIMqHbIX UeHTPOB CU", a TaKme PmMa-UllOHHOrO nblpOqHOr0 UeHTpa B MOHOKpRCTaJIJIaX aHaTa3a. AJIH BCeX UeHTpOB AOJIy-geHbI KOHCTaHTbI CIIMH-I' aMZIJIbTOHMaHOB H BOJIHOBbIe (EYHKUMM OCHOBHOrO COCTO-IIIeTIEe H MeXaHI13M 3apfIAOBO~ KoMneHCaUMM. RHHR. 06cymnaro~cf1 YCJIOBHR BxomnemH, nonomeHme npnlclecablx MOHOB B pe-

Investigations of EPR parameters for Cr3+ and Mn4+ ions in anatase (TiO2) crystals

“…In general, the slightly negative ∆g i arises from two causes: (i) the large contribution to the g factor due to the spin-orbit (SO) coupling parameter of the ligand via covalence effect in the case of a ligand having a large SO coupling parameter (where a two-SO-parameter model including both the SO coupling parameter of 3d n ion and that of ligand should be used [4,5]) and (ii) the large contribution to the g factor from the charge transfer (CT) mechanism in the case of the central 3d n ion having high valence state and hence low CT energy level [6] (thus, the influence of the CT excited state on the g factors of the ground state cannot be neglected and so both crystal field (CF) and CT mechanisms should be considered [7,8] [10]), the second cause may be important. In order to confirm the above opinion and to study the relative importance of the CT mechanism not only for the g factors, but also for zero-field splitting D and the change of the relative importance of these with the valence state of 3d 3 ions, in this paper we establish the complete high-order perturbation formulas including both CF and CT mechanisms for the EPR parameters of 3d 3 ions in tetragonal octahedral clusters. From these formulas, the EPR parameters g || , g ⊥ and D for Cr 3+ and Mn 4+ ions in anatase crystals are calculated.…”

“…The electron paramagnetic resonance (EPR) spectra of some transition metal ions in anatase crystals have been obtained. For example, the EPR spectra of 3d 3 ions Cr 3+ and Mn 4+ at the tetragonally octahedral Ti 4+ site of anatase crystals were measured and their EPR parameters (g factors g || and g ⊥ and zero-field splitting D) were obtained [2,3]. It is found that the g-shift ∆g i (= g i − g e , where i = || and ⊥ and g e = 2.0023 is the spin-only value) for the Mn 4+ center is slightly negative and the absolute value |∆g i | of the Mn 4+ center is smaller than that of the Cr 3+ center [2,3].…”

“…For example, the EPR spectra of 3d 3 ions Cr 3+ and Mn 4+ at the tetragonally octahedral Ti 4+ site of anatase crystals were measured and their EPR parameters (g factors g || and g ⊥ and zero-field splitting D) were obtained [2,3]. It is found that the g-shift ∆g i (= g i − g e , where i = || and ⊥ and g e = 2.0023 is the spin-only value) for the Mn 4+ center is slightly negative and the absolute value |∆g i | of the Mn 4+ center is smaller than that of the Cr 3+ center [2,3]. In general, the slightly negative ∆g i arises from two causes: (i) the large contribution to the g factor due to the spin-orbit (SO) coupling parameter of the ligand via covalence effect in the case of a ligand having a large SO coupling parameter (where a two-SO-parameter model including both the SO coupling parameter of 3d n ion and that of ligand should be used [4,5]) and (ii) the large contribution to the g factor from the charge transfer (CT) mechanism in the case of the central 3d n ion having high valence state and hence low CT energy level [6] (thus, the influence of the CT excited state on the g factors of the ground state cannot be neglected and so both crystal field (CF) and CT mechanisms should be considered [7,8] [10]), the second cause may be important.…”

Redox Behavior of VI B Transition Metal Ions in Rutile TiO2 Solid Solutions: An XRD and EPR Study

“…Cr4 in tetrahedral coordination has been detected at ¹477 K on silica surface (32,33), in Cr-doped phosphates (34,35 ) and in irradiated Cr-doped sulfates (36). Isolated Cr4 in a distorted octahedral con"guration has been found in SrTiO after treatment in oxygen or chlorine at 1000 K (37) and in anatase single crystal after irradiation at 77 K (38). Hence, when a strong Cr"O bond is formed, Cr4 is stabilized probably because of its high formal charge and very small ionic radius, i.e., its very high ionic potential.…”

ESR study of the stabilization of V4+ ions in TiO2 (anatase)

“…Exchange spectra of V 4+ (S) associates appear with increasing vanadium concentration in rutile [3][4][5][6]. The formation of isolated and exchange spectra of V 4+ ions on the anatase surface has been observed by ESR [7][8][9]. However, the existence of solid state solutions of vanadium in anatase is still an open question.…”