Impurities and electron localization in V<sub>2</sub>O<sub>5</sub> crystals

Grunin, V. S.; Patrina, I. B.; Zonn, Z.N.

doi:10.1002/pssb.2221150226

Cited by 5 publications

(10 citation statements)

References 17 publications

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“…In practice the 9,-value (or g, on other designation) is almost always bigger than go = 2.0023. This fact evidences the hole deviation from the crystal plane leading toithe mixing of all wave functions and sp3-hybridization of the oxygen orbitals, s z = go 9 9% = go + f l ( 4 7 where a is the isotropic term and b, c reflect the anisotropy of the hyperfine structure. These constants are shown in Tables 1 and 2 .…”

Section: Hole-type Centresmentioning

confidence: 86%

“…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…”

mentioning

confidence: 81%

“…The number of these centres depends only on the number of the electron trapping sites. Since the hole centres and Mo5+ ions appear in Na,Mo,O, a t the same time and the numbers of both defects are increased by doping with calcium, it can be assumed that the electron trapping centres in Na2Mo,0, are Mo6+ ions in the vicinity of the Me2+ cations substituting Na+ and compensated by the impurity oxygen [6]. I n the course of reduction these levels are filled with electrons and Mo5+ ions are formed.…”

Section: Hole-type Centresmentioning

confidence: 99%

“…In During the reduction the electrons are localized on Mo, Cr, or V depending on the kind of impurity, but Nb4+ and Ta4+ ions are never formed in the crystals doped with Nb and Ta. The dependence of the electron localization on the kind of the substitutional impurity ions was also observed in V205 [8], TiO, and Nb,05 [9]. An attempt to connect the unpaired electron density distribution with the electronegativity value a of the main and impurity cations was undertaken in [ 8 ] .…”

Section: Electron Centresmentioning

confidence: 99%

“…The dependence of the electron localization on the kind of the substitutional impurity ions was also observed in V205 [8], TiO, and Nb,05 [9]. An attempt to connect the unpaired electron density distribution with the electronegativity value a of the main and impurity cations was undertaken in [ 8 ] . a = qeff/r$,ys, where q e f f is the effective charge of the cation, rphys is the physical radius [ll].…”

Section: Electron Centresmentioning

confidence: 99%

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Impurities and Charge Compensation in Some Molybdenium Oxides

Grunin

Patrina

1984

Physica Status Solidi (b)

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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

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Section: Hole-type Centresmentioning

confidence: 86%

mentioning

confidence: 81%

Section: Hole-type Centresmentioning

confidence: 99%

Section: Electron Centresmentioning

confidence: 99%

Section: Electron Centresmentioning

confidence: 99%

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Impurities and Charge Compensation in Some Molybdenium Oxides

Grunin

Patrina

1984

Physica Status Solidi (b)

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Small Polaron Mobility in α‐Li_xO₅

Sánchez

Henry

Morineau

et al. 1984

Physica Status Solidi (b)

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ESR and dc conductivity measurements are performed on a Li,V,O, (z = 0.001) single crystal in the temperature range 4 to 293 K. They suggest that at low temperature, the unpaired electron remains localized in the field of lithium ion and is equally delocalized over four vanadium sites leading to the formation of a bound polaron characterized by a 29 hyperfine lines ESR spectrum. As the temperature is raised bound polarons are freed from the electrostatic field and the electrical properties of the sample above 250 K mainly arise from the hopping of free polarons between the vanadium sites. A comparison with previous measurements on non-stoichiometric V,O, shows that the activation energy corresponding to the hopping process of free polarons does not depend on the nature of the paramagnetic defect, but it appears that the energy needed to extract the bound polaron from the Coulomb field of the defect decreases when the overall radius of the defect increases.EPR und Messungen der Gleichstromleitfilhigkeit werden an einem Li,V,O, (z = 0,00l)-Einkristall im Temperaturbereich 4 bis 293 K durchgefuhrt. Sie zeigen, daB bei tiefen Temperaturen das ungepaarte Elektron lokalisiert bleibt im Feld des Lithiumions und gleichformig delokalisiert ist iiber vier Vanadiumpliitze, was zu der Bildung eines gebundenen Polarons fuhrt, das durch ein EPR-Spektrum mit 29 Hyperfeinlinien charakterisiert ist. Bei Temperaturerhohung werden die gebundenen Polaronen aus dem elektrostatischen Feld befreit und die elektrischen Eigenschaften der Probe oberhalb 250 K ruhren hauptsiichlich vom Hopping-Mechanismus der freien Polaronen zwischen den Vanadiumpliitzen her. Ein Vergleich mit friiheren Messungen an nichtstochiometrischem V,O, zeigt, daB die dem HoppingprozeS freier Polaronen entsprechende Aktivierungsenergie nicht von der Art des paramagnetischen Defekts abhiingt, sondern es scheint, daS die Energie, die zur Befreiung des gebundenen Polarons aus dem Coulombfeld des Defekts notwendig ist, abnimmt, wenn der Gesamtradius des Defekts wiichst.

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