Electronic structure of an oxygen vacancy in lithium niobate

DeLeo, Gary G.; Dobson, Joel L.; Masters, Mark; Bonjack, Leslie H.

doi:10.1103/physrevb.37.8394

Cited by 34 publications

(18 citation statements)

References 37 publications

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“…The color change in the DC cycled hot-pressed LLZNO confirms that the LLZNO is unstable in contact with Li ( Figure 5B). Similar discoloration phenomena has been observed in Li3NbO4 where darkening, such as the formation of yellow and black regions, resulted from the reduction of Nb 5+ to Nb 4+ (Zverev et al, 1972;DeLeo et al, 1988;Nyman et al, 2010). The color change of the hot-pressed LLZNO may be similar to what is observed in the reduction of Nb 5+ in Li3NbO4, which resulted in the loss of Li and/or O.…”

Section: Characterization After Cyclingsupporting

confidence: 72%

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

et al. 2016

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The electrochemical stability of Li6.5La3Zr1.5Nb0.5O12 (LLZNO) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO) against metallic Li was studied using direct current (DC) and electrochemical impedance spectroscopy (EIS). Dense polycrystalline LLZNO (ρ = 97%) and LLZTO (ρ = 92%) were made using sol-gel synthesis and rapid induction hot-pressing at 1100°C and 15.8 MPa. During DC cycling tests at room temperature (± 0.01 mA/cm 2 for 36 cycles), LLZNO exhibited an increase in Li-LLZNO interface resistance and eventually short-circuiting while the LLZTO was stable. After DC cycling, LLZNO appeared severely discolored while the LLZTO did not change in appearance. We believe the increase in Li-LLZNO interfacial resistance and discoloration are due to reduction of Nb 5+ to Nb 4+ . The negligible change in interfacial resistance and no color change in LLZTO suggest that Ta 5+ may be more stable against reduction than Nb 5+ in cubic garnet versus Li during cycling.

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Section: Characterization After Cyclingsupporting

confidence: 72%

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

et al. 2016

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“…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: Discussionsupporting

confidence: 60%

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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“…3). While the formation energy of oxygen vacancy in LiNbO 3−δ is higher, oxygen vacancy has been widely observed in LiNbO 3−δ in experiments [59][60][61][62].…”

Section: B Supercell Calculationsmentioning

confidence: 99%

Coexistence of polar displacements and conduction in doped ferroelectrics: An ab initio comparative study

Xia

Chen

2019

Phys. Rev. Materials

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Polar metals are rare because free carriers in metals screen electrostatic potential and eliminate internal dipoles. Degenerate doped ferroelectrics may create an approximate polar metallic phase.We use first-principles calculations to investigate n-doped LiNbO 3 -type oxides (LiNbO 3 as the prototype) and compare to widely studied perovskite oxides (BaTiO 3 as the prototype). In the rigid-band approximation, substantial polar displacements in n-doped LiNbO 3 persist even at 0.3 e/f.u. ( 10 21 cm −3 ), while polar displacements in n-doped BaTiO 3 quickly get suppressed and completely vanish at 0.1 e/f.u. Furthermore, in n-doped LiNbO 3 , Li-O displacements decay more slowly than Nb-O displacements, while in n-doped BaTiO 3 , Ba-O and Ti-O displacements decay approximately at the same rate. Supercell calculations that use oxygen vacancies as electron donors support the main results from the rigid-band approximation and provide more detailed charge distributions. Substantial cation displacements are observed throughout LiNbO 3−δ (δ = 4.2%), while cation displacements in BaTiO 3−δ (δ = 4.2%) are almost completely suppressed. We find that conduction electrons in LiNbO 3−δ are not as uniformly distributed as in BaTiO 3−δ , implying that the rigid-band approximation should be used with caution in simulating electron doped LiNbO 3type oxides. Our work shows that polar distortions and conduction can coexist in a wide range of electron concentration in n-doped LiNbO 3 , which is a practical approach to generating an approximate polar metallic phase. Combining doped ferroelectrics and doped semiconductors may create new functions for devices.

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Electronic structure of an oxygen vacancy in lithium niobate

Cited by 34 publications

References 37 publications

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

First-principles and semiempirical calculations forFcenters inKNbO3

Coexistence of polar displacements and conduction in doped ferroelectrics: An ab initio comparative study

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