Dielectric properties of Na 1Àx Li x NbO 3 ceramics from powders obtained by chemical synthesis (original) (raw)
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Dielectric properties of Na 1− x Li x NbO 3 ceramics from powders obtained by chemical synthesis
Ceramics International, 1999
Ultra-®ne powders of Na 1Àx Li x NbO 3 (x=0; 0.06; 0.09; 0.12 ) were synthesized by the Polymeric Precursors Method. Such powders had their orthorhombic structures determined by X-ray diraction and their surface area determined by BET isotherms (less than 10 m 2 g À1 ). Densi®cation was followed by dilatometric study. The powders, calcined at 700 C for 5 h, were sintered at 1290 C during 2 h under ambient atmosphere with no application of extra pressure. The samples with relative densities higher than 95% were analyzed by impedance spectroscopy at room temperature, under a signal amplitude of 1 V rms . Dielectric constants of about 180 and dielectric loss factor of about 0.03 were measured showing small dependence with frequency. The electrical properties were similar to those obtained for samples sintered by hot pressing. #
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.
Ceramics International, 2013
In this paper, lead-free (Na 0.474 K 0.474 Li 0.052)(Nb 0.948 Sb 0.052)O 3 ceramics were synthesized by a conventional solid-state reaction route. The effects of sintering temperature on the crystal structure, microstructure, densification, dielectric properties, and ferroelectric properties of the KNNLS ceramics were addressed. X-ray diffraction patterns and Raman spectrum indicated a transition from orthorhombic to tetragonal phase during the sintering temperature region. This transition is attributed to the migration of Li between the matrix grain and grain boundary. Scanning electron microscopy study revealed increased grain size and enhanced densification with increasing sintering temperature. The density of the ceramics sintered at 1080 1C reached a maximum value of 4.22 g/cm 3. KNNLS ceramics sintered at an optimum temperature of 1080 1C exhibited high piezoelectric properties, that is 242 pC/N for d 33 , 0.42 for k p and 18.2 mC/cm 2 for P r .
Journal of Physics and Chemistry of Solids, 2011
Na 1 À x Li x NbO 3 ceramics with composition 0.05 r x r 0.30 were prepared by solid-state reaction method and sintered in the temperature range 1100-1150 1C. These ceramics were characterised by X-ray diffraction as well as dielectric permittivity measurements and Raman spectroscopy. Dielectric properties of ceramics belonging to the whole composition domain were investigated in a broad range of temperatures from 300 to 750 K and frequencies from 0.1 to 200 kHz. The Rietveld refinement powder X-ray diffraction analysis showed that these ceramics have a single phase of perovskite structure with orthorhombic symmetry for x r0.15 and two phases coexistence of rhombohedral and orthorhombic above x ¼ 0.20. The evolution of the permittivity as a function of temperature and frequency showed that these ceramics Na 1 À x Li x NbO 3 with composition 0.05 r x r 0.15 present the classical ferroelectric character and the phase transition temperature T C increases as x content increases. The polarisation state was checked by pyroelectric and piezoelectric measurements. For x ¼ 0.05, the piezoelectric coefficient d 31 is of 2pC/N. The evolution of the Raman spectra was studied as a function of temperatures and compositions. The results of the Raman spectroscopy study confirm our dielectric measurements, and they indicate clearly the transition from the polar ferroelectric phase to the non-polar paraelectric one.
Structural and dielectric properties of Na1−x Ba x Nb1−x (Sn0.5Ti0.5) x O3 ceramics
Lead-free (1x)NaNbO 3 /xBa(Ti 0.5 Sn 0.5 )O 3 (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKa radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10 B x B 0.15 and relaxor one for compositions in the range 0.15 \ x B 0.30. Temperatures T C or T m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d 31 of 42.146 pC N -1 was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1.
Ceramics International, 2016
In the present work, the microstructures of YSZ electrolyte films, which were sintered at various temperatures in the range of 1300e1600 C, were investigated. First, a suitable and uniform film was deposited on the surface of NiOeYSZ composite by EPD. After the consequence sintering, the surfaces of deposited YSZ films were observed by SEM. In addition, other characteristics of the YSZ electrolyte films such as surface roughness and morphology of the sintered films were investigated by AFM. The ability of ionic transfer and permeability of the YSZ electrolyte was examined by electrochemical impedance spectroscopy at different temperatures. It seems that the YSZ electrolyte sintered at 1400 C was appropriate for SOFCs applications, because this film had the minimum impedance, minimum roughness and the maximum conductivity. Furthermore, the temperature of 1400 C was the minimum temperature in which a dense film of YSZ was formed uniformly on the surface of anode and coated it completely.
2008
Abstract High density sodium lithium niobate lead free ceramics near the morphtropic phase boundary [Na x Li 1− x NbO 3,(LNN), x= 0.12] were prepared by the solid state reaction method. XRD patterns showed that the lattice structures were changed after polarization. The temperature dependence of the dielectric constant and dielectric loss, pyroelectric coefficient and DSC curves of LNN ceramics showed that there exist three phase transitions from room temperature up to the Curie temperature.
Structural and dielectric characterization of LiNbO 3 nano-size powders obtained by Pechini method
Lithium niobate is an artificially synthesized material with wide technological applications, due to its numerous physical properties, such as: ferroelectricity, birefringence and large pyroelectric, piezoelectric, non-linear, acousto-optic, electro-optic and photo-elastic coefficients. It also exhibits very strong bulk photovoltaic and photo refractive effects. In the present work, LiNbO 3 powders were prepared by the Pechini (sol–gel) method. The heat-treatment of the base amorphous powders, at 450 °C promotes the formation of LiNbO 3 crystalline phase. The electrical characterization, in function of the heat-treatment time, shows that the dc conductivity depends on the quantity of crystalline phase, which increases with the increase of heat-treatment time. The sample treated for 96 h shows a dielectric constant value of *35, at low frequencies. A dielectric relaxation phenomenon independent of the temperature of measurement was detected in the samples treated at 48 and 96 h, shifting to higher frequencies with the increase of the heat-treatment time.
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