ChemInform Abstract: LiZnNb 4 O 11.5 : A Novel Oxygen Deficient Compound in the Nb-Rich Part of the Li 2 O-ZnO-Nb 2 O 5 System (original) (raw)
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Journal of Solid State Chemistry
a-PbO 2 related structure Superspace approach Supercell (3+ 1)D structure type X-ray diffraction Transmission electron microscopy a b s t r a c t A novel lithium zinc niobium oxide LiZnNb 4 O 11.5 (LZNO) has been found in the Nb-rich part of Li 2 O-ZnO-Nb 2 O 5 system. LZNO, with an original a-PbO 2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a =17.8358(9)Å, b=15.2924(7)Å, c=5.0363(3)Å and g=96.607(5)1 or as a-PbO 2 -like with lattice constants a=4.72420(3)Å, b=5.72780(3)Å, c=5.03320(3)Å, g=90.048(16)1 and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated a-PbO 2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112 1 /n(ab0)00) as well as a supercell (space group P2 1 /b). The superspace description allows us to consider the LZNO structure as a member of the proposed a-PbO 2 -Z (3 + 1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li 2 O-ZnO-Nb 2 O 5 system are predicted on the basis of this detailed HRTEM analysis.
LiZnNb4O11.5: A novel oxygen deficient compound in the Nb-rich part of the Li2O–ZnO–Nb2O5 system
Journal of Solid State Chemistry, 2010
a-PbO 2 related structure Superspace approach Supercell (3+ 1)D structure type X-ray diffraction Transmission electron microscopy a b s t r a c t A novel lithium zinc niobium oxide LiZnNb 4 O 11.5 (LZNO) has been found in the Nb-rich part of Li 2 O-ZnO-Nb 2 O 5 system. LZNO, with an original a-PbO 2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a =17.8358(9)Å, b=15.2924(7)Å, c=5.0363(3)Å and g=96.607(5)1 or as a-PbO 2 -like with lattice constants a=4.72420(3)Å, b=5.72780(3)Å, c=5.03320(3)Å, g=90.048(16)1 and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated a-PbO 2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112 1 /n(ab0)00) as well as a supercell (space group P2 1 /b). The superspace description allows us to consider the LZNO structure as a member of the proposed a-PbO 2 -Z (3 + 1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li 2 O-ZnO-Nb 2 O 5 system are predicted on the basis of this detailed HRTEM analysis.
Applied Physics B: Lasers and Optics, 1999
We report the dependence of the unit cell parameters and the EO coefficients on Zn doping in opticaldamage-resistant LiNbO 3 :Zn crystals. Both properties depend in a non-monotonic manner on the Zn content. This is accounted for by different types of Zn ion incorporation into the lattice depending on the Zn concentration in the melt. Extrema observed in the concentration dependence of the EO coefficients at about 2-3 and 6.4 mol.% Zn correlate with an unusual concentration dependence of the unit cell parameters a and c. The low-concentration anomalies may be accounted for by a decrease of the Li vacancy concentration due to the Zn incorporation into Li sites. Anomalies at high concentrations are obviously due to a partial incorporation of Zn ions on Nb sites, which is reflected in the structure data. Anomalies in the concentration dependence of other optical properties at about 6-7 mol.% Zn reported recently are obviously related to a change in the localization of the Zn ions. The combination of high EO coefficients with a reduced optical damage for these concentrations make these crystals attractive for applications as Q-switching or electrooptical modulation.
No difference in local structure about a Zn dopant for congruent and stoichiometricLiNbO3
Physical Review B, 2016
We compare extended x-ray absorption fine structure (EXAFS) data at the Zn K edge for a low concentration of Zn (0.7 mol%) in a stoichiometric crystal with that for higher Zn concentrations (nominally 5 and 9 mol%) in congruent LiNbO 3 (LNO). Note that stoichiometric and congruent LNO have significantly different optical properties. We find no significant difference in the local structure about Zn out to 4Å for the two types of crystals and different dopant levels. Although some earlier theoretical models suggest a self-compensation model with 75% of Zn on a Li site and 25% Zn on Nb, we find no clear evidence for a significant fraction of Zn on the Nb site, and estimate at most 2%-3% of Zn might be Zn Nb .
New conducting phase in the Li2O-ZnO-Nb2O5 system: Existence conditions
Russian Journal of Inorganic Chemistry, 2009
The conducting phase Li 6 ZnNb 4 O 14 in the Li 2 O -ZnO -Nb 2 O 5 system has been obtained by solid-phase synthesis from Li 3 NbO 4 , Li 1x NbO 3 , and LiZnNbO 4 . The new phase exists in the temperature range of (904 ± 5)-(1145 ± 5)°C. Quenching the synthesis product from 960°C yields this phase in a metastable state at room temperature. The Li 6 ZnNb 4 O 14 phase has been characterized by thermal analysis, chemical analysis, and X-ray powder diffraction. The ohmic resistance of ceramic Li 6 ZnNb 4 O 14 has been determined by complex impedance measurements. The activation energy of conduction, derived from the temperature dependence of conductivity, is E a = 0.273 ± 0.001 eV. The conductivity of the phase at 300°C is 1.2 × 10 -2 S cm -1 .
On the lithiation reaction of niobium oxide: structural and electronic properties of Li1.714Nb2O5
Monoclinic -Nb2O5 was chemically lithiated by reaction with n-butyllithium, mimicing the product of electrochemical discharge of a niobium oxide cathode vs. a Li anode. The compound was investigated by neutron powder diffraction (D2B equipment at ILL, France) and its structure was Rietveld refined in space group P2 to wRp=0.045, locating the Li atoms inserted in the -Nb2O5 framework. The ensuing chemical formula is Li12/7Nb2O5. A part of Li atoms are more strongly bonded (five coordinated O atoms), a part are less (coordination number = 4). Starting from the experimental structure, first-principles periodic calculations based on the hybrid B3LYP functional were performed. The electrochemical voltage of Li insertion was computed to be 1.67 V, fully consistent with the experimental 1.60 V plateau vs. capacity. An analysis of the electron band structure shows that lithiation changes the insulating oxide into a semi-metal; some of the extra electrons inserted with lithium become spin-polarized and give the material weak ferromagnetic properties.
Ab-initiostudies on Li doping, Li-pairs, and complexes between Li and intrinsic defects in ZnO
Journal of Applied Physics, 2012
First-principles density functional calculations have been performed on Li-doped ZnO using allelectron projector augmented plane wave method. Li was considered at six different interstitial sites (Li i), including anti-bonding and bond-center sites and also in substitutional sites such as at Zn-site (Li zn) and at oxygen site (Li o) in the ZnO matrix. Stability of Li Zn over Li i is shown to depend on synthetic condition, viz., Li Zn is found to be more stable than Li i under O-rich conditions. Hybrid density functional calculations performed on Li Zn indicate that it is a deep acceptor with (0/-) transition taking place at 0.74 eV above valence band maximum. The local vibrational frequencies for Li-dopants are calculated and compared with reported values. In addition, we considered the formation of Li-pair complexes and their role on electronic properties of ZnO. Present study suggests that at extreme oxygen-rich synthesis condition, a pair of acceptor type Li Zn-complex is found to be stable over the compensating Li i þ Li Zn pair. The stability of complexes formed between Li impurities and various intrinsic defects is also investigated and their role on electronic properties of ZnO has been analyzed. We have shown that a complex between Li Zn and oxygen vacancy has less formation energy and donor-type character and could compensate the holes generated by Li-doping in ZnO. V
Effect of Ni-doping Charge on Structure and Properties of LiNbO 3
2016
Phase formation and structural properties of Ni-doped Li 0.976-x Nb 1.005-x/5 Ni x O 3 (0 ≤ x ≤ 0.1) ceramics prepared by solid-state reaction method, are investigated in a temperature range from 400 to 900 °C. X-ray diffraction patterns indicate that single phase was formed for lithium niobate ceramics. It was shown that the unit-cell volume of the hexagonal phase decreased with increasing nickel concentration from 0 to 3% Ni charge and increased above 3%. No secondary phases were observed in Ni-doped powder of LiNbO 3 for all concentrations compared with that of undoped sample. These results indicate that the Ni 2+ ion was substituted for niobium and lithium ions in the hexagonal phase. The addition of Ni 2+ promotes densification of lithium niobate ceramics. Raman spectra show that the samples were well crystallized with high purity. It was noticed that the increase of Ni-doping causes the decreasing of resistivity at high temperatures, but it has no influence of activation energy.
Ceramics International, 2019
When Fe is doped in ZnO, a situation of charge imbalance is created due to the higher charge of Fe 3+. A charge balance may be obtained by co-doping Li + 0.5 Fe 3+ 0.5 combinations. A solid solution of Zn 1-x (Fe 0.5 Li 0.5) x O (0 ≤ x ≤0.03125) is synthesized with this viewpoint. The crystallites belong to a wurtzite P6 3 mc space group, with lattice parameters a, b and c increasing nominally for x = 0.0156 and thereafter remaining invariant. The size varies in the range ~ 60-142 nm. Interstitials of Li and Zn ions are formed. Along with Fe 3+ substitution these defects are reasons for O interstitials. These oxygen interstitials increase the red emission while reduction of oxygen vacancies reduces the green emission. These point defects create structural distortion and strain which can generate Zn vacancies. Bandgap reduces due to shallow defects. Mid-bandgap states due to oxygen interstitials and Fe 3d-O 2p hybridization result in NIR emission. On the other hand the crystal surface deforms due to Li addition which hardens the materials. A weak ferromagnetism appears at very low temperature which is enhanced by Li + addition. Long range
Physical Review B, 2004
The (LixNa1-x)NbO3 perovskite solid solutions are investigated using synchrotron x-ray diffraction and Raman spectroscopy in order to clarify the structural changes in the concentration range 0<=x<=0.145 at room temperature. The orthorhombic antiferroelectric P phase (space group Pbma, Z=8) exists up to x=0.02 and in the concentration interval 0.02<=x<=0.03 we have confirmed a previously reported transition to the orthorhombic ferroelectric Q