New conducting phase in the Li2O-ZnO-Nb2O5 system: Existence conditions (original) (raw)
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Ceramics International, 2012
In this work, Li-modified KNN ceramic compositions ((K 0.5 Na 0.5) 1Àx Li x)NbO 3 with x = 0.03, 0.04, 0.05, 0.06, 0.65 and 0.07 were prepared by a conventional solid-state mixed-oxide method. The structural phase formation and microstructure were characterized by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM). It has been found that a morphotropic phase boundary (MPB) between orthorhombic phase and tetragonal phases should exist between compositions with Li contents of 6-6.5%. The Curie temperature (T c) of the ceramics shifted to higher temperature with increasing Li content. The room temperature dielectric constant was also seen to be higher than the pure KNN ceramics. In addition, the ferroelectric properties were found to enhance at near MPB compositions. This study clearly showed that the addition of Li could improve the dielectric and ferroelectric properties in (K 0.5 Na 0.5)NbO 3 ceramics.
Conduction below 100 °C in nominal Li6ZnNb4O14
Journal of Materials Science, 2015
The increasing demand for a safe rechargeable battery with a high energy density per cell is driving a search for a novel solid electrolyte with a high Li ? or Na ? conductivity that is chemically stable in a working Li-ion or Na-ion battery. Li 6 ZnNb 4 O 14 (LZNO) has been reported to exhibit a r Li [ 10-2 S cm-1 at 250°C, but to disproportionate into multiple phases on cooling from 850°C to room-temperature. An investigation of the room-temperature Li-ion conductivity in a porous pellet of a multiphase product of a nominal LZNO composition is shown to have bulk r Li & 3.3 9 10-5 S cm-1 at room-temperature that increases to 1.4 9 10-4 S cm-1 by 50°C. 7 Li MAS NMR spectra were fitted to two Lorentzian lines, one of which showed a dramatic increase with increasing temperature. A test for water stability indicates that Li ? may move to the particle and grain surfaces to react with adsorbed water as occurs in the garnet Li ? conductors.
Journal of Advanced Dielectrics, 2017
Polycrystalline perovskite structured (Li[Formula: see text] (Na[Formula: see text] K[Formula: see text])[Formula: see text] (Nb[Formula: see text]Ta[Formula: see text] Sb[Formula: see text] O3 ceramics with [Formula: see text], 0.005 and 0.01 mole excess Na concentration were prepared by solid state sintering method. The present study relates the role of excess Na addition with the stoichiometry, density, structure, dielectric and ferroelectric properties of the samples. X-ray diffraction (XRD) pattern exhibits single phase orthorhombic structure. The characteristic Raman modes were observed due to translational modes of cations and vibrational modes of NbO6 octahedra and no structural phase transition were observed. This confirms the formation of single phase perovskite structure and is consistent with XRD results. The dielectric permittivity increases about two times, while dielectric loss decreases by four times for [Formula: see text] composition. The electrical measurements ca...
Structure, Dielectric and Impedance Studies of Li Doped (K0.5Na0.5)NbO3 Ceramics
Polycrystalline, lead free (K 0.5 Na 0.5)NbO 3 and (K 0.5 Na0.5) 0.49 Li 0.02 NbO 3 ceramics were synthesized using solid-state reaction method. X-ray diffraction studies confirmed the formation of mono-phasic ceramics. During dielectric studies some anomalies were observed around temperatures 155 ºC and 439 ºC for (K 0.5 Na0.5) 0.49 Li 0.02 NbO 3. Complex impedance spectroscopy (CIS) technique was used to investigate the bulk (grain interior) and grain boundary contributions to the impedance as a function of temperature and frequency. CIS studies revealed that the electrical relaxation process was temperature dependent and non-Debye type. AC conductivity studies revealed that conductivity was mainly due to the ionized oxygen vacancies in (K 0.5 Na0.5) 0.49 Li 0.02 NbO 3 ceramics.
Journal of Applied Physics, 2013
Temperature-dependent dielectric permittivity of lead-free (Li x Na 1-x)NbO 3 for nominal x = 0.04-0.20, prepared by solid state reaction followed by sintering, was studied to resolve often debated issue pertaining to exactness of morphotropic phase boundary (MPB) location along with structural aspects and phase stability in the system near MPB. Interestingly, a diffuse phase transition has been observed in the dielectric permittivity peak arising from the disorder induced in A-site and structural frustration in the perovskite cell due to Li substitution. A partial phase diagram has been proposed based on temperature-dependent dielectric permittivity studies. The room temperature piezoelectric and ferroelectric properties were investigated and the ceramics with x = 0.12 showed relatively good electrical properties (d 33 = 28 pC/N, k p = 13.8%, Q m = 440, P r = 12.5 μC/cm 2 , E C = 43.2 kV/cm, T m = 340 o C). These parameter values make this material suitable for piezoelectric resonator and filter applications. Moreover, a high dielectric permittivity (εʹ r = 2703) with broad diffuse peak near transition temperature along with low dielectric loss (< 4%) in a wide temperature range (50-250 o C) found in this material may also have a potential 2 application in high-temperature multilayer capacitors in automotive and aerospace related industries.
Electrical and structural characterization of (KxNa1−x)NbO3ceramics modified with Li and Ta
Journal of Applied Crystallography, 2011
Na 1Àx)NbO 3 ceramics modified with Li + and Ta 5+ have been produced using the mixed-oxide synthesis method. Synchrotron X-ray diffraction measurements were made on the samples from 12 K to temperatures above their ferroelectricparaelectric transition points with 10 K measurement steps. Rietveld refinement was used to refine the patterns. Depending on the composition and temperature, rhombohedral phases, orthorhombic phases, tetragonal phases, cubic phases and two-phase mixtures were obtained. Space groups R3c (161), Amm2 (38), P4mm (99) and Pm3m (221) and their combinations were used to refine the rhombohedral, orthorhombic, tetragonal, cubic and mixed phases, respectively. Li + addition suppressed the formation of the rhombohedral low-temperature phase and increased the Curie temperature. This is attributed to the size difference in ionic radii of the A-site elements, which leads to increased atomic polarizability and increased interaction with the B-site element. Li + and Ta 5+ co-doping led to a wide temperature range of coexistence between the orthorhombic and tetragonal phases. Electrical characterizations by dielectric and hysteresis measurements were used to compare with the results from the structural studies. research papers J. Appl. Cryst. (2011). 44, 1080-1089 Henry E. Mgbemere et al. Modified (K x Na 1Àx)NbO 3 ceramics 1081
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.
Electrical and structural characterization of (K x Na 1− x )NbO 3 ceramics modified with Li and Ta
Journal of Applied Crystallography, 2011
of Li + and Ta 5+ on the crystal structure and electrical properties of (K x Na 1-x)NbO 3 ceramics has been investigated. The results from Rietveld refinement show that the presence of Li + suppresses the formation of the orthorhombic-tetragonal phase transition to low temperatures. Phase coexistence over wide temperature range may help to explain why the piezoelectric properties in doped (K x Na 1-x)NbO 3 ceramics are higher than in the undoped samples.