Dielectric loss and phase transition of sodium potassium niobate ceramic investigated by impedance spectroscopy

The dielectric permittivity of Na_0.80K_0.20NbO₃ ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 °C, in the frequency range 5 Hz–13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200 °C and the second one positioned at around 400 °C, which was associated to Curie’s temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na_0.80K_0.20NbO₃ showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10² kHz.     

Ionic conduction and dielectric properties of yttrium doped LiZr2(PO4)3 obtained by a Pechini-type polymerizable complex route

We report on the ion transport properties of Li_1+xZr_2-xY_x(PO₄)₃ (0.05?≤ x?≤?0.2) NASICON type nanocrystalline compounds prepared through a Pechini-type polymerizable complex method. Structural properties were characterized by means of powder X-ray diffraction, Raman spectroscopy and electron microscopy with selected area electron diffraction. Impedance spectroscopy was utilised to investigate the lithium ion transport properties. Y³⁺ doped LiZr₂(PO₄)₃ compounds showed stabilized rhombohedral structure with enhanced total ionic conductivity at 30?°C from 2.87?×?10^?7 S?cm^?1 to 0.65?×?10^?5 S?cm^?1 for x=0.05 to 0.20 respectively. The activation energies of Li_1+xZr_2-xY_x(PO₄)₃ show a decreasing trend from 0.45?eV to 0.35?eV with increasing x from 0.05 to 0.20. The total conductivity of these compounds is thermally activated, with activation energies and pre-exponential factors following the Meyer-Neldel rule. The tanδ peak position shifts to the high-frequency side with increasing yttrium content. Scaling in AC conductivity spectra shows that the electrical relaxation mechanisms are independent of temperature.     

Phase evolution,dielectric and impedance spectroscopic study of SrNb2O6 columbite phase

Strontium niobate SrNb₂O₆ has been synthesized by columbite solid-state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and temperature as well as frequency dependence of dielectric and impedance study. XRD analysis indicates single phase formation of the compound with ∼180 nm crystallite size. Study of SEM micrographs pointed out that prepared material has good sinterability and enough density with homogeneous grain distribution. It was found that the magnitude of relative dielectric constant (?_r) was relatively high with low dielectric loss compared with reported columbite compounds. Impedance spectroscopy was used to characterize the electrical behavior of the compound. AC impedance spectrum results indicate that the relaxation mechanism of the material is temperature dependent and has bulk and grain boundary contribution in different temperature ranges.     

Structural phase transition,impedance spectroscopy and narrow optical band Gap in 1-xKNbO3-xBaSc12Nb12O3

In the progress of exploring lead-free ferroelectric perovskites, a new solid solution of $\left(1-x\right)\mathrm{}\mathrm{K}\mathrm{N}\mathrm{b}{\mathrm{O}}_3-\mathrm{}x\mathrm{}\mathrm{B}\mathrm{a}\left({\mathrm{S}\mathrm{c}}_{\frac{1}{2}}\mathrm{}{\mathrm{N}\mathrm{b}}_{\frac{1}{2}}\right)O_3$ is synthesized using solid state method. The effect of Ba and Sc codoping on structural phase transition, dielectric, ferroelectric, electrical, and optical properties is systematically studied. A narrow band gap of 1.98eV is observed at x?=?0.05. On further increase in x, the optical band gap increases due to increased strain. The crystal symmetry changes from orthorhombic at x?=?0.00 to tetragonal phase at x?≤?0.15, remains in pseudocubic phase for 0.15?<?x?<?0.35, and finally transforms to the cubic symmetry at x?≥?0.35. A new Raman active mode evolves at 180?${\mathrm{c}\mathrm{m}}^{-1}$ at x?=?0.15, which could be the TO or LO phonon of ${\mathrm{A}}_1$ symmetry. The electrical microstructure of the prepared electroceramics at room temperature has been investigated using impedance spectroscopy. This newly synthesized ferroelectric perovskite material has promising potential applications for photocatalysis and photovoltaics, especially under the visible light spectrum.     

Raman and dielectric spectroscopic analysis of magnetic phase transition in Y(Fe0.5Cr0.5)O3 multiferroic ceramics

Here, we report the Raman and dielectric spectroscopic studies as a function of temperature of orthorhombically distorted Y(Fe_0.5Cr_0.5)O₃ (YFC) ceramics, measured from 80 to 300 K. The dc-magnetization measurements under field cooled (FC)-zero field cooled (ZFC) protocol indicate a small onset of magnetic ordering at T_N∼270 K. The field dependent magnetization plot recorded at 50 K, 150 K and 200 K show a clear opening in hysteresis loops. The linear dependence of magnetization plot at high field without any saturation of magnetization indicates the coexistence of weak ferromagnetic (WFM) component within the canting antiferromagnetic (CAFM) matrix. Temperature evolution of Raman line-shape parameter of B_2g(4) phonon mode clearly exhibits an anomalous behavior of phonon shift near T_N∼270 K, indicating the spin-phonon coupling in the ceramics. From the temperature dependent dielectric permittivity (ε(T)) study, two dielectric relaxation peaks are detected below 200 K and above 250 K. The appearance of former relaxation peak is responsible for polaronic conduction mechanism, while the later one is associated with magnetic phase transition which might be relevant to the presence of magnetoelectric coupling in YFC ceramics. The observed P-E hysteresis loops at room temperature indicate weak ferroelectric nature of the ceramics.     

Effect of hot-pressing sintering on thermal and electrical properties of AlN ceramics with impedance spectroscopy and dielectric relaxations analysis

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO₂–CeF₃ additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO₃ and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics.     

DC conductivity and AC impedance of Mn doped magnesia alumina spinel (MgAl2-2xMn2xO4) over a large temperature range

MgAl_2-2xMn_2xO₄ (MAMO) with x = 0-0.12 was synthesized in a single-phase form by solid-state reaction. XRD analysis showed that the samples had the cubic center structure of the Fd-3 m space group. Electrical properties of the samples were studied over the temperature range of 300 K∼1073 K. The results showed that the DC conductivity (σ_DC) increased from 10⁻¹¹S/cm at 300 K (MAMO, x = 0) to 10^-3S/cm at 1073 K (MAMO, x = 0.12). The equivalent circuit of the complex impedance spectra suggested that the relaxation of charge carriers was of non-Debye type. The conduction was mainly caused by grain boundaries and the capacitance was mainly attributed to polarization. The complex permittivity values (ε’ and ε’’) were increased by two orders of magnitude with the increase in Mn content and temperature over the measured frequency range (1 Hz-1 MHz). Therefore, doping with Mn could be applied to modify the electrical properties of MAMO at high temperature.     

High frequency impedance of poly(ethylene oxide) and related polymers doped with lithium perchlorate

High frequency complex impedance measurements at room temperature have been used to obtain dielectric constants, sample dimension ratios and conductivities for poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, doped with LiClO₄. The corrections required to compensate for artefacts due to instrumentation (leads, cables, etc.) at high frequencies are presented. It is concluded that an area/length ratio (A/l) of about 300 cm is preferable for high frequency work. Dielectric constants varied by less than an order of magnitude over a variety of samples, so that the conductivity of an irregularly shaped sample can be estimated from the dielectric relaxation frequency. It was also concluded that the depression of the impedance semicircle for semi-crystalline PEO was due mainly to the microstructure.     

Dielectric and impedance spectroscopy analysis of lead-free (1-x)(K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3-xBaTiO3 ceramics

(1-x)(K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃-xBaTiO₃ (labeled as (1-x)KNLNTS- xBT, x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) lead-free ceramics were prepared by a solid-state sintering method. As the BT content increased, the phase of ceramics changed from orthorhombic (0.00 ≤ x ≤ 0.02) to orthorhombic-tetragonal (0.02 < x < 0.06) structure, and finally turned into tetragonal (0.06 ≤ x ≤ 0.10) structure. The Curie-Weiss law and modified Curie-Weiss law were applied to analyzing dielectric properties. With the increase of BT content, the relaxation degree increased, which indicated that the ceramics shown a excellent relaxation behavior. For 0.9KNLNTS- 0.1BT ceramics, the dispersion coefficient γ reached the maximum of 1.73, which is hugely attractive for lead-free relaxor ferroelectrics. From its variation of impedance spectroscopy with temperature, it was found that the relaxation and conduction behavior were associated with the thermal activation, and the oxygen vacancies were the potential ionic carriers. Moreover, through Arrhenius fitting, the activation energy of 0.9KNLNTS- 0.1BT ceramic was 0.82(6) eV, indicating that the oxygen vacancy concentration for the ceramics was high.     

Dielectric and impedance spectroscopy of Sr(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Sr(Bi_0.5Nb_0.5)O₃ was prepared using a high-temperature solid-state reaction technique. Preliminary X-rays diffraction studies exhibit the formation of a single-phase compound in the orthorhombic crystal system. The study of microstructure of gold-coated pellet by scanning electron microscopy (SEM) shows well-defined and homogeneous distribution of grains on the surface of the sample. Detailed studies of dielectric parameters (i.e., ε_r and tan δ) of the compound as a function of temperature at selected frequencies reveal that the values of these parameters are almost independent of temperature. Studies of impedance and related parameters exhibit that these electrical properties of the material are strongly dependent on temperature, and bear a good correlation with the microstructure of the material. The decrease in value of bulk resistance on increasing temperature suggests the existence of negative temperature co-efficient of resistance (NTCR) in the material. Studies of electric modulus show the presence of hopping conduction mechanism in the material with non-exponential-type of relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius- and NTCR- types of behaviors of the material. The ac conductivity spectrum provides a typical-signature of an ionic conducting system, and is found to obey Jonscher′s universal power law.     

Dielectric and structural studies of ferroelectric phase evolution in dipole-pair substituted barium titanate ceramics

Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025, and 0.05 have been prepared by conventional solid-state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole-pair substitution concentration on the macroscopic dielectric properties. Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ for x ≥ 0.01 possesses diffuseness parameters comparable to Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) and recently reported (Ba_0.97Pr_0.03)(Ti_0.9425Ce_0.05)O₃ (BPTC), yet it lacks the frequency and temperature dependence of T_m necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga_0.05,Ta_0.05]Ti_0.9}O₃ possesses a relative permittivity, ɛ_r, of 700 ± 16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [−75°C, 120°C]. In comparison to BaTiO₃, Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ possesses enhanced electrical resistivity at and above room temperature. In situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion, and phase transition temperature (T_c) of each composition within the temperature range [RT, 1000°C], thus linking the dielectric properties with the material's structure. These studies have been corroborated by temperature-dependent Raman spectroscopy to compare the T_c determined by electrical and structural characterization. The properties of Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ are discussed in context with available models that describe donor and acceptor dopants spatially separated in the parent matrix, inter-relating lattice parameter, Curie temperature, and other material properties.     

Microstructure,conductivity and mechanical properties of calcia stabilized zirconia ceramics obtained from nanosized precursor and reduced graphene oxide doped precursor powders

In the work 12CaO-88ZrO₂ (12CSZ, mol%) ceramics was manufactured both from nanopowder, obtained via cryochemical technique, and composite precursor 12CSZ?+?0.25?wt% rGO (reduced graphene oxide). Via SEM, XRD and Raman spectroscopy the detailed investigation of the effect of the precursor type and intermediate processing on the microstructure and electrical conductivity of ceramics was carried out. It was shown that rGO is completely removed during the annealing at 1550?°C for 3?h in air with no effect on the high ionic conductivity of ceramics. The use of nanosized powder and the additional processing step results in vacuum dense solid electrolytes characterized by well-formed cubic zirconia based solid solution, thin discontinuous grain boundaries and rather high ionic conductivity. The addition of rGO leads to slight microhardness (HV) decrease comparing to ceramics manufactured from the nanosized precursor. As a result, a new technique for zirconia based solid electrolytes having both high electrical conductivity at high temperatures and sufficient mechanical properties was suggested.     

Electrochemical impedance spectroscopic study of the intercalation of lithium and sodium ions into polyparaphenylene in carbonate-based electrolytes

Electrochemical impedance spectroscopy is used to investigate the electrochemical intercalation of lithium and sodium ions into polyparaphenylene under galvanostatic conditions in carbonate-based electrolyte. The evolution of the charge transfer resistance was studied at various selected potentials both during the reduction and the oxidation processes in order to control the stoichiometry of the intercalated compounds. The reversibility of the intercalation process, the effect of the cycling and the stability of the intercalated materials in the electrolyte as a function of the time were examined. A significant decrease of the charge transfer resistance occurs during the intercalation. That is related to an increase of the conductive state especially for the richest compounds Na_0.46(C₆H₄) and Li_0.50(C₆H₄).     

Influence of the forming electrolyte on the electrical properties of tantalum and niobium oxide films: an EIS comparative study

The electrochemical oxidation of Ta and Nb and the dielectric behaviour of the oxide films thus formed were investigated in the following electrolytes: H2SO4, HNO3, H3PO4 and NaOH. Characterization of the films was carried out by means of potentiodynamic current–potential profiles (in the range 0–8V) and electrochemical impedance spectra (in the range 0.1Hz–100kHz). The a.c. response of the oxide films was modelled as a single layer structure on the basis of an equivalent circuit with constant phase elements (CPE). The dependence of the oxide resistance and oxide capacitance with potential is also reported.     

Vibrational spectroscopic studies of cation effects in low molecular weight poly(propylene oxide) complexed with lithium, sodium and potassium thiocyanate

This paper presents the results of room temperature Raman scattering and infrared transmission investigations of an approximately 450 average molecular weight poly(propylene oxide), PPO, complexed with varying concentrations of lithium, sodium and potassium thiocyanate. The strength of interaction between the metal cation and the polymer is observed to increase in the order Li>Na>K. Spectral changes in the O---H stretching region show that the cations interact with the alcoholic oxygen atoms as well as the ether oxygen atoms. Frequency shifts in the C---H stretching region combined with the growth of splittings and structure in lower frequency bands suggest that increasing complexation is accompanied by changes in the polymer backbone dynamics and structure. The metal-oxygen stretching band is easily identified in the infrared transmission spectra. Finally, cation-dependent frequency shifts of the thiocyanate ion bands indicate the formation of contact ion pairs coordinated at the nitrogen end of the anion.     

An ac impedance spectroscopic study of Mg-doped LiCoO2 at different temperatures: electronic and ionic transport properties

An ac impedance spectroscopic study of LiMg_0.05Co_0.95O₂, prepared by sol-gel process, is presented. The results are interpreted on the basis of the equivalent circuit proposed for LiCoO₂ oxide that takes into account the ionic and electronic transport processes. The results demonstrate that the intercalation/deintercalation reaction occurs through two-steps processes involving an adatom mechanism that may be described in terms of partially desolvated lithium ions adsorbed/desorbed from the electrode surface and insertion/loss of an electron from the conduction band of the host followed by diffusion of Li⁺ to/from the lattice intercalation site. Mg doping of LiCoO₂ affects the electrochemical and electronic properties of the pristine oxide by facilitating the insulator-to-conductor transitions that are responsible of the phase transition in the undoped material.     

Intrinsic and extrinsic effects near orthorhombic-tetragonal phase transition in barium titanate ceramics doped with small amounts of zirconium

Pure BT and BT doped with 1 and 2 mol% Zr, with orthorhombic-tetragonal (O-T) phase transitions near room temperature were prepared, with different grain sizes, by conventional ceramic method, at various sintering temperatures. Intrinsic and extrinsic effects of Zr addition on structural, dielectric, piezoelectric and ferroelectric properties of BT ceramics, near O-T phase transition were studied. In coarse grained ceramics, the intrinsic effects manifested in low field measurements (dielectric and piezoelectric constants), were reduced by Zr addition, while the extrinsic effects which control the high field response (remanent polarization and coercive field) were significantly enhanced. Instead, in fine grains ceramics, of either pure or doped BT, the extrinsic effects related to increased domain wall and grain boundaries density were dominant in both low and high field measurements, overlapping Zr effects. The results were explained in terms of crystal anisotropy correlated with grain size effects.     

Synthesis and characterization of Sr2+ and Mg2+ doped LaGaO3 by co-precipitation method followed by hydrothermal treatment for solid oxide fuel cell applications

In the present study, LSGM (La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8) powder has been synthesized using precipitation route followed by hydrothermal treatment. Quantitative phase analyses of different powders, have been done by Rietveld analyses of the XRD data and they reveal formation of single phase orthorhombic LSGM at 1400 °C, 8 h. Morphology of the calcined powder and microstructure of the sintered pellets are observed by transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. Thermal analysis has been carried out to find out the thermal expansion co-efficient. Successive electrical characterization of the 99% dense sintered pellet has been done by impedance spectroscopic analysis. The diffused semicircles observed in the Nyquist plots have been simulated as (RQ)(RQ) circuit and the total ionic conductivity obtained is found to be the highest for LSGM synthesized by similar routes.     

Synthesis and electrical properties of the (PVA)0.7(KI)0.3·xH2SO4 (0 ≤ x ≤ 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H₂SO₄ concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H₂SO₄ concentrations were analyzed. A maximum dc conductivity of 1.05 × 10⁻³ S cm⁻¹ has been achieved at ambient temperature for electrolytes containing 5 M H₂SO₄. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO₂ solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758 V was obtained for 5 M H₂SO₄ based Zn/SAPE/MnO₂ battery.