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-

V. S. GRUNM et al. : Impurities and Electron Localization in V20, phys. stat. sol. (b) 116, 545 (1983) Subject classification: 13.4 and 19; 22.6 545 I . V . Grebenshikov Institute of Silicate Chemistry, Acudemy of Sciences of the USSR, Leningrad1) Impurities and Electron Localization in V,O, Crystals BY V. S. GRUNIN, I. R. PATEINA, and Z. N. ZONN V,Od crystals doped with different impurities of the Mn+ (A = 1 to 6) type are investigated by the EPR method. It follows from the experiment that all the paramagnetic defects are connected with the impurities present in the crystals. The main paramagnetic centre in V,O, is an electron localized on two 51V nuclei. There is no local compensation of its charge and so it easily destroys in the course of oxidation. It is shown by hyperfine structure investigation that the electron states are localized in a wide temperature range (4.2 to 290 K). The substitutional impurity tends to occupy the vanadium positions near the V-V pair. A complex paramagnetic centre is created with electron density distribution dependence on the donor-acceptor characteristics of the cations. This results in the nonequivalence of the electron interactions with different vanadium atoms, in different values of the HFS constants for differently doped crystals, and in different valency of the impurity cations. Centres of this type are locally compensated and therefore stable to oxidation or reduction. MeToAoM 3nP HCWeaOBaHbI MOHOKPHCTaJIJIbI v,05 C npIIMeCRMH KaTHOHOB M"+ (n = 1 nO6). YCTaHOBdIeHO, 9TO BCe napaMarHIITHble ne@eKTbl T a K HJIM HHa9e CBfi3aHbI C 30BaHHblfi H a AByX Rapax v5'. 3 T O T Ae@eKT H e HMeeT JIOKaJIbHOB KOMneHCal(HH 3apIIAa H CTPYKTYPbI CneKTpa 3TOr0 QeHTpa B IIIHPOKOM TeMIlepaTJTHOM HHTepBaJIe 4,2 A 0 290 K CBHneTeJIbCTB3;eT 0 TOM, YTO BO BCeB MCCJIeAOBaHHOfi o6nac~w TeMnepaTyp XapaKTep JIOKaJIH3a4MZi 3JIeKTpOHa OCTaeTCH HeH3MeHHblM. n P H M e C U 3aMeweHHfl HMeH)T TeHReHUHH) npHMecmm B KpHcTanae. O C H O B H O~ napaMaraHTxibi8 uewp B V , O , -a n e~~p o~, noHaminemo p a 3 p y m a e~c~ B OmcnnTenbH~x JWIOBHIIX. Xopouree paapeureane csepxToHKom BxornAeaMfi B BaeanMeame y3nb1, pacnonomeHmie B6JIH3H ne@ema paccMoTpeHHoro T m a , npusonrr K 06pa30BaHHIO caomnoro napaMarHnTHoro uempa, pacnpeneneme 3JIeKTpOHHOfi IlJIOTHOCTH B KOTOPOM OnpeneJlfieTCH COOTHOIUeHHeM AOHOpHO-aKUenTOp-HblX CBO#CTB 06pa3yrou~x er0 KaTHOHOB. 3 T a 3aBMCIIMOCTb IIpORBJIfieTCH B He3KBHBa-JleHTHOCTH B3aHMORe~CTBUR 3JIeKTpOHa C pa3JIH9HbIYkI R n p a M U BaHanLiH, B pa3JIIIqHbIX 3Ha9eHHHX KOHCTaHT CTC AJIH MOHOKPHCTaJIJIOB C pa3JIHcIHbIMH IIPHMeCRMH, B BaJIeHTHOM COCTOIIHHH npHMeCHbIX KBTHOHOB. UeHTPbI 3TOr0 T H n a JIOKaJlbHO KOMfleHCHPOBaHbI H C T~~H J I~H~I IlO OTHOLlleHUH) K TepMOO6pa60TKe B OKHCJlUTeJIbHOfi H BOCCTaHOBIITeJIbHOfi cpenax.

V. S. GRUNIN et al.: Temperature Dependence of the EPR Spectra of Cr3+ and Cr5+ 765 phys. stat. sol. (b) 98, 765 (1980) An investigation is made of EPR spectra of CaV,O, and BaV20, single crystals doped with chromium. It is found that the point symmetry of the paramagnetic Cr3+ and C P ions depends on temperature. It follows from t,he symmetry of the Cr5+ spectrum in BaV,O, and its superhyperfine structure a t T = 77 K that the Cr5+ ion is displaced to one of two neighbouring V atoms. The observed change of the impurity ion symmetry cannot be explained both by the off-centre ion theory and the Jahn-Teller effect. HCCJIeEOBaHbI CneKTpbI 3nP MOHOKpUCTaJIJIOB CaV,O, U BaV,O, C EpUMeCbIO XpOMa. 3KCEepUMeHT nOKa3aJI, 9 T O TOge9HaH CUMMeTpUX IlapaMarHUTHbIX IlOHOB Cr3r U Cr6+ MeHHeTCH C TeMIlepaTypO6. H3 CHMMeTPUH CneKTpa UOHOB Cr5' B BaV,O, U ero CylIep-CBepXTOHHOfi CTpYKTYPbI npU T = 77 K CJleEyeT, ' XTO 3TOT MOH CMeUeH K OAHOMY M3 EByX COCeHHUX aTOMOB BaHaEUH. H~~J I K I @~M O~ kl3MeHeHHe CMMMeTpUK npUMeCHbIX UOHOB He MOIHeT 6bITb 06' bHCHeHO B PaMKaX MOAenU HeUeHTpanbHOCTU UJIU 3@@eKTa HHa-Tennepa.s = 112, g, = 1.983 k 0.001, A , = (2.24 & 0.02) X J , A, = (1.67 +_ 0.02) X J , A , = (0.4 & 0.2) x J , A; = (1.21 & 0.02) x J , A , = (7.04 k 0.02) X lopz6 J, J . g, = 1.901 & 0.001 . A; = (9.92 5 0.02) X The 2 and z axes of gand A-tensors for two non-equivalent centres are in the (001) plane and form the angles k0.262 rad with the [010] and [loo] axes, respectively, the y-axis being the corninon one and coincides with the [OOl] axis of crystal. The 2' and z' axes of the SHFS form the angle +0.350 rad with the z and z axes, 9' ) I [OOl] is common. 2.2 Temperuture dependence of the spectra 2.2.1 Cr3+ When the temperature was decreased below about 270 K every line of the Cr3+ ion spectrum in CaV,O, was doubled. The distance of the pairs increases when lowering temperature to about 200 I< and is constant for further decrease of temperature.

No abstract

The role of impurities in the defect formation in MOO, and Na,Mo,O, crystals is discussed. The EPR spectra of the X-ray and uv-irradiation centres are investigated. The constants of the appropriate spin-Hamiltonians are obtained. It is shown that the localization radius of an electron (or a hole) exceeds the interatomic distances, therefore the EPR spectra have a low symmetry with noncoincident axes of the Aand g-tensors. The unpaired density distribution depends on the characteristics of the lattice and impurity cations such as the electronegativity, the coordination number, and the degree of the local environment symmetry distortion.30pOB. YCTaHOBJIeHO , 4 T O PaCnpe~eJIeHHt? HeCIIapeHHOfi CnIIHOBOg IIJIOTHOCTH 3aBHCHT OT CBOfiCTB OCHOBHbIX II IIpHMeCHbIX HaTHOHOB, TaHHX KaK 3JIeKTpooTpHqaTeJIbHOCTb, HOOpHHHaUHOHHOe YHCJIO, CTeIIeHb HCHa?KeHHfI JIOKaJIbHOrO OKpymeHHH Ei OHa B HPIIC-npaKTmecm BcerHa npeBocxoHm MemaToMHBe paccTommfi, B p e 3 y n b~a~e qero qeHTpa1 Tanne. MOO, crystals under certain growth conditions [l]. The defects of that kind were detected, for example, in MOO, crystals grown in H, or 0, atmospheres [2]. The lattice sites and the charge compensation of Fe3+ [3], Cu2+ [l], V4+ 141, and Cr5+ [5] ions in MOO, crystals were examined. There are hole centres in Vand Nb-doped MOO, crystal, too. The interactions with 51V and 93Nb nuclei were observed in their EPR spectra. The number of these defects changes in the course of oxidation or reduction [4]. The same effects were observed in Na,Mo,O, crystals. The numbers of Mo5+ and Cr5+ ions in these crystals depend on the atmosphere of the thermal treatment [6, 71.It was shown that the appearance of electrons in the lattice is due to the decompensation of Me2+ impurity charges on the Na+ sites. The electron density distribution depends on the kind of the impurity cation. This is a general property of all transition metal oxides. The electron localization is different for differently doped crystals as was clearly shown by the experiment for V,05 with a wide set of impurity cations [8].Nat. Makarova 2, 199 164 Leningrad, USSR.23 physica (b) 123/1