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Varnhorst, T.; Schirmer, O. F.; Kröse, H.; Scharfschwerdt, Raphaela; Kool, Th. W.

doi:10.1103/physrevb.53.116

Cited by 67 publications

(41 citation statements)

References 25 publications

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“…Refs. 35,36); the only exception known to us is an X α cluster calculation of F centers in LiNbO 3 . 37 Electron defects similar to what we have observed here are known, in particular, in partly covalent SiO 2 crystals (e.g., in the so-called E ′ 1 center an electron is also not localized inside V O but its wave function mainly overlaps with the sp 3 orbital centered on the neighboring Si atom 38 ).…”

Section: Discussionmentioning

confidence: 99%

First-principles and semiempirical calculations forFcenters inKNbO3

et al. 1997

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The linear muffin-tin-orbital method combined with density functional theory (local approximation) and the semiempirical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism are used for the study of the F centers (O vacancy with two electrons) in cubic and orthorhombic ferroelectric KNbO3 crystals. Calculations for 39-atom supercells show that the two electrons are considerably delocalized even in the ground state of the defect. Their wave functions extend over the two Nb atoms closest to the O vacancy and over other nearby atoms. Thus, the F center in KNbO3 resembles electron defects in the partially-covalent SiO2 crystal (the so-called E ′ 1 center) rather than usual F centers in ionic crystals like MgO and alkali halides. This covalency is confirmed by the analysis of the electronic density distribution. Absorption energies were calculated by means of the INDO method using the ∆ self-consistent-field scheme after a relaxation of atoms surrounding the F center. For the orthorhombic phase three absorption bands are calculated to lie at 2.72 eV, 3.04 eV, and 3.11 eV. The first one is close to that observed under electron irradiation. For the cubic phase, stable at high temperatures, above 708 K, only the two bands, at 2.73 eV and 2.97 eV, are expected.

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Section: Discussionmentioning

confidence: 99%

First-principles and semiempirical calculations forFcenters inKNbO3

et al. 1997

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“…The ESR study of KNbO 3 doped with Ti 4+ gives a proof that holes could indeed be trapped by such negatively charged defects [3]. For example, in BaTiO 3 , hole polarons were also found that are bound to Na and K alkali ions replacing Ba and thus forming a negatively charged site attracting a hole [4]. Primary candidates for such defects are cation vacancies.…”

Section: Introductionmentioning

confidence: 96%

Large scale computer modelling of point defects in ABO ₃ perovskites

Eglitis

Kotomin

Börstel

2005

phys. stat. sol. (c)

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We present results for basic intrinsic defects: F-type electron centers, free and bound electron and hole polarons in ABO 3 perovskites. Both one-site (atomic) and two-site (molecular) hole polarons are expected to coexist, characterized by close absorption energies. Shell Model (SM) and intermediate neglect of differential overlap (INDO) calculations of the F center diffusion indicate that the relevant activation energy is quite low, ca. 0.8 eV. Further INDO calculations support the existence of self-trapped electron polarons in PbTiO 3 , BaTiO 3 , KNbO 3 , and KTaO 3 crystals. The relevant lattice relaxation energies are typically 0.2 eV, whereas the optical absorption energies are around 0.8 eV. We also used the INDO method for modelling the atomic and electronic structure of KNb x Ta 1-x O 3 (KTN) perovskite solid solutions. The Nb impurities in KTaO 3 reveal off-center displacements starting with the smallest calculated concentrations. The calculated magnitude of the displacement is close to the EXAFS observation. Using the calculated energy gain for several concentrations of Nb in KTN, we construct the Ginzburg-Landau-type functional for the excess energy. The coefficients of this functional are concentration-dependent. This dependence allows us to define the type of concentration-induced phase transition in KTaO 3 alloyed by Nb.

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“…replaces the Ba 2+ and had a negative charge relating to lattice. This negative charge stimulated strong hole-lattice interaction and result in hole localization [13].…”

Section: Resultsmentioning

confidence: 99%

“…The energy decrease determined by Jahn-Teller symmetric distortion may be not sufficient for self-trapping of a hole. Similarly to BaTiO 3 , where the presence of a negatively charged impurity ion stimulates self-trapping of a hole on the neighboring oxygen ion [13], the presence of a self-trapped electron in PWO will also stimulate self-trapping of a hole on the nearby ions. But, compared to ZnWO 4 , self-trapping of the hole will be delayed.…”

Section: +mentioning

confidence: 98%

Formation of luminescence centres under excitation with electron beams in PbWO ₄ and ZnWO ₄ crystals

Chernov

Millers

Grigorjeva

2005

phys. stat. sol. (c)

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PACS 78.55.Hx, 78.90+t The leading edge of intrinsic luminescence pulse in PbWO 4 and ZnWO 4 single crystals is studied. The rise of luminescence intensity is observed after excitation with electron beam pulse. The luminescence rise is shown to be a result of luminescence center formation via electron-hole recombination within spatially correlated pairs. An electron of a geminate electron-hole pair of PbWO 4 crystal self-traps and stimulates self-trapping of a hole at a close distance. In the ZnWO 4 crystal a hole of a geminate electron-hole pair self-traps and stimulates self-trapping of the electron producing a W 5+ center at a short distance. The risetime of luminescence depends on spatial separation of recombining components. It is short even at 80 K (100 ns in PbWO 4 and 10 ns in ZnWO 4 ). The reasons for different rise time and different spatial distribution of electron and hole self-trapped centers are discussed.

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O−holes associated with alkali acceptors inBaTiO3

Cited by 67 publications

References 25 publications

First-principles and semiempirical calculations forFcenters inKNbO3

First-principles and semiempirical calculations forFcenters inKNbO3

Large scale computer modelling of point defects in ABO ₃ perovskites

Formation of luminescence centres under excitation with electron beams in PbWO ₄ and ZnWO ₄ crystals

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O−holes associated with alkali acceptors inBaTiO3

Cited by 67 publications

References 25 publications

First-principles and semiempirical calculations forFcenters inKNbO3

First-principles and semiempirical calculations forFcenters inKNbO3

Large scale computer modelling of point defects in ABO 3 perovskites

Formation of luminescence centres under excitation with electron beams in PbWO 4 and ZnWO 4 crystals

Contact Info

Product

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Large scale computer modelling of point defects in ABO ₃ perovskites

Formation of luminescence centres under excitation with electron beams in PbWO ₄ and ZnWO ₄ crystals