Dielectric relaxation and ac conductivity of double perovskite oxide Ho2ZnZrO6

Double perovskite oxide holmium zinc zirconate Ho₂ZnZrO₆ (HZZ) is synthesized by solid state reaction technique under a calcination temperature of 1100 °C. The crystal structure has been determined by powder X-ray diffraction, which shows monoclinic phase at room temperature. The variation of dielectric constant (ε′) and loss tangent (tan δ) with frequency is carried out assuming a distribution of relaxation times. The frequency corresponding to loss tangent peak is found to obey an Arrhenius law with activation energy of 89.7 meV. The frequency-dependant electrical data are analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary electric modulus shows the temperature-independent nature of the distribution of relaxation times. Nyquist plots are drawn to identify an equivalent circuit and to know the bulk and interface contributions.     

Dielectric relaxation and ac conduction in multiferroic TbMnO3 ceramics: Impedance spectroscopy analysis

Polycrystalline samples of Tb_1−xAl_xMnO₃ (x = 0, 0.1, 0.2) have been synthesized by means of standard high-temperature solid-state reaction technique. Detailed studies on the effect of compositional variation of aluminum (Al) on the electrical behavior (complex impedance Z*, complex modulus M*, and relaxation mechanisms) of the parent TbMnO₃ have been performed by using the nondestructive complex impedance spectroscopy technique at temperatures above room temperature. In the temperature range covered, the impedance plots signalize that the grains are the unique responsible for the conduction mechanism of the concerned material. The impedance spectra are well modeled in terms of electrical equivalent circuit with a grain resistance (R_g) and constant phase element impedance (Z_CPE). The conductivity data of the undoped and Al-doped samples are well fitted by the universal Jonscher's power law. The resulting fitting parameters indicate that for the studied samples, the hopping process occurs between neighboring sites. Activation energy values for dc conductivity are calculated for undoped and Al-doped samples and found to decrease when Al is incorporated. In turn, the emergence of single arc in the complex modulus spectrum for all the compositions of Al suggests that for the studied samples only one type of relaxation behavior is present at the selected temperatures. A non-Debye-type relaxation is clearly verified. The relaxation process in the present samples seems to be composition and temperature dependent, particularly at higher frequencies.     

Dielectric dispersion in PbO-Sb2O3-As2O3:V2O5 glasses

Dielectric properties, viz. dielectric constant ε′, loss tan δ and a.c conductivity σ_ac (over a wide range of frequency and temperature) and dielectric breakdown strength of PbO-Sb₂O₃-As₂O₃ glasses doped with V₂O₅ (ranging from 0 to 0.5 mol%) are studied. Analysis of these results, based on optical absorption and ESR spectra, indicates that the insulating strength of the glasses is comparatively high when the concentration of V₂O₅ is about 0.3 mol% in the glass matrix.     

The impedance spectroscopic study and dielectric relaxation in A(Ni1/3Ta2/3)O3 [A=Ba,Ca and Sr]

We present the results of impedance spectroscopic study with its analytical interpretations in the framework of electric modulus formalism for Barium Nickel Tantalate Ba(Ni_1/3Ta_2/3)O₃ (BNT), Calcium Nickel Tantalate Ca(Ni_1/3Ta_2/3)O₃ (CNT) and Strontium Nickel Tantalate Sr(Ni_1/3Ta_2/3)O₃ (SNT) synthesized by the solid-state reaction technique. The results of powder X-ray diffraction study reveal that BNT and SNT crystallize in cubic structure with lattice parameter a=4.07 Å and 3.98 Å respectively, whereas CNT crystallizes in monoclinic structure having lattice parameters, a=5.71 Å, b=13.45 Å and c=5.47 Å with β=118.3°. The logarithmic angular frequency dependence of the real part of complex dielectric permittivity and loss tangent as a function of temperature indicate significant dielectric relaxation in the samples, which have been explained by the Debye theory. The frequency dependence of the loss peak and the imaginary part of electrical modulus are found to obey the Arrhenius law. The relaxation mechanism of these samples is modeled by the Cole–Cole equation. This confirms that the polarization mechanism in BNT, CNT and SNT is due to the bulk effect arising in semiconductive grains. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures but relaxation frequency is strongly temperature dependent. The normalized peak positions of tan δ/tan δ_m and M″/M″_m versus log ω for BNT, CNT and SNT do not overlap completely and are very close to each other. These indicate the presence of both long-range and localized relaxation. Due to their high dielectric constant and low loss tangent, these materials may find several technological applications such as in capacitors, resonators, filters and integrated circuits.     

Electrical characteristics and low-temperature sintering of BiFeO3-modified Pb(Zr,Ti)O3–Pb(Fe2/3W1/3)O3–Pb(Mn1/3Nb2/3)O3 ceramics with ZnO addition

Effects of ZnO addition on electrical properties and low-temperature sintering of BiFeO₃-modified Pb(Zr,Ti)O₃–Pb(Fe_2/3W_1/3)O₃–Pb(Mn_1/3Nb_2/3)O₃ were investigated. The investigations revealed that the sintering temperature can be decreased to 950 °C, and the favorable properties were obtained with 0.10 wt% ZnO added ceramics. The electrical properties were as follows: d₃₃ = 313 pC/N, K_p = 0.56, tan δ = 0.0053, ε_r = 1407 and T_c = 295 °C, which showed that this system was a promising material for the multilayer devices application.     

Electrical analysis of a newly synthesized rare earth double perovskite oxide: Sr2CeNbO6

A polycrystalline rare earth double perovskite oxide, strontium cerium niobate, Sr₂CeNbO₆ (SCN) is synthesized by solid state reaction technique for the first time. Impedance spectroscopy is employed to determine the electrical parameters (resistance (R), capacitance (C) and relaxation time (τ)) of SCN in a temperature range from 303 to 703 K and in a frequency range from 100 Hz to 1 MHz. The spectrum of imaginary part of complex impedance (Z″) at each temperature exhibits one relaxation peak. The modified Cole-Cole equation is used (experimental data is fitted with this model) to describe these relaxation peaks. Scaling behaviour of Z″ suggests that the relaxation describes the same mechanism at the entire temperature range. Impedance data of SCN that have capacitive and resistive components is represented by Nyquist diagram. The experimental impedance data is fitted using equivalent RC circuit at various temperatures. The grain conduction and τ follow an Arrhenius law associated with activation energy 0.87 and 0.88 eV, respectively.     

AC conductivity and dielectric relaxation in Ba(Sm1/2Nb1/2)O3 ceramic

The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant (ε′) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN.     

Dielectric relaxation and a.c. conduction phenomena of PbO-PbF2-B2O3 glasses doped with FeO

PbO-PbF₂-B₂O₃ glasses containing different concentrations of FeO have been prepared. The glasses are characterized by X-ray diffraction and differential thermal analysis. The dielectric properties viz., dielectric constant, loss, conductivity, over a moderately wide range of frequency and temperature and dielectric breakdown strength have been investigated. The results of these studies have been analyzed in the light of different oxidation states of iron with the aid of the data on IR, ESR, optical absorption and magnetic susceptibility measurements. The analysis shows that iron ions exist mainly in Fe³⁺ state, occupy tetrahedral positions and increase the insulating strength of the glass if FeO is present in smaller concentrations. However, if FeO is present in higher concentrations in the glass matrix, (i) the dielectric relaxation intensity has been observed to increase, (ii) the intensity and the half width of the ESR signal has been observed to decrease and (iii) the value of magnetic moment (evaluated from magnetic susceptibility) has been observed to drop to a value of 4.6 μ_B from 5.7 μ_B. From these results it has been concluded that in this concentration range, iron ions exist mainly in divalent state.     

Dielectric properties for the ordered-perovskite cuprate Sr2Cu(Re0.69Ca0.31)O6

Dielectric properties are reported on polycrystalline cubic ordered-perovskite cuprate Sr₂Cu(Re_0.69Ca_0.31)O₆ in the frequency range 10 Hz-100 kHz at temperature from 300 to 500 K. Both the dielectric permittivity and dielectric loss factor are found to be frequency and temperature dependent. The enhanced value of the low frequency dielectric permittivity is associated to ionic polarization and interfacial phenomena. The material is found to possess significantly high dielectric permittivity. The calculated ac conductivity suggests semiconducting behaviour for the Sr₂Cu(Re_0.69Ca_0.31)O₆.     

Dielectric properties and temperature stability of BaTiO3 co-doped La2O3 and Tm2O3

The influence of La₂O₃ and Tm₂O₃ co-doping on the dielectric properties and the temperature stability of BaTiO₃ was investigated. BaTiO₃ ceramics were prepared with the compositional formula of (Ba_1−xLa_x)(Ti_1-x/4−yTm_y)O₃. La₂O₃ and Tm₂O₃ co-doping in BaTiO₃ mainly had effects on an increase in the dielectric constant and the temperature stability, respectively. The increase of La₂O₃ concentration and the decrease of Tm₂O₃ concentration in BaTiO₃ resulted in a decrease of lattice parameter and tetragonality because La³⁺ ion substituting for Ba site is smaller than Ba²⁺ ion and Tm³⁺ ion substituting for Ti site is larger than Ti⁴⁺ ion. With the increase of La₂O₃ and the decrease of Tm₂O₃, the dielectric constant of BaTiO₃ was enhanced in spite of the reduction of tetragonality. P-E hysteresis measurements revealed that this phenomenon was based on the improvement of remanent polarization with the increase of La₂O₃ concentration. The introduction of excess Tm₂O₃ in BaTiO₃ suppressed the grain growth and BaTiO₃ ceramics showed higher temperature stability due to the stable tetragonal structure and the small grain size with the increase of Tm₂O₃ concentration.     

Physical properties of BaMg1/3Nb2/3O3-BaCo1/3Nb2/3O3 solid solutions

Structural, electric and magnetic properties of Ba₃Mg_1−xCo_xNb₂O₉ based dielectric ceramic compounds have been studied. The samples, prepared by a solid state reaction method, were characterised by X-ray powder diffraction (XRPD), electron microscopy (SEM), dielectric (ε(T)) and magnetic measurements (χ⁻¹(T)). The XRPD analyses showed that the crystal structure of these compounds does change by the increase of substitution degree, passing from a superstructure hexagonal-type, (no. 164), space group (SG) to a simple structure cubic-type, (no. 221), SG. However, the evolution of the elementary unit cell lattice parameter can be followed and it exhibit a linear increasing tendency with increase in the substitution, indicating the existence of a solid solution through out the investigated range of substitution (0-1). The microstructure analysis shows a variation in the grain size and also the porosity of the samples with the degree of substitution. The results are in good agreement with that of dielectric measurements, which also showed that the dielectric constant (ε) increases with the increase of cobalt content. The magnetic characterization of cobalt substituted samples showed an antiferromagnetic type super-exchange interaction between these magnetic ions. At the same time, the values of effective magnetic momentum (μ_eff) are close to the value that corresponds to Co²⁺ free ions. The study highlights the possibility of modelling these materials by substitutions, in order to improve properties of negative-positive-zero (NPO) type dielectric applications.     

Impedance study of giant dielectric permittivity in BaFe0.5Nb0.5O3 perovskite ceramic

Single-phase BaFe_0.5Nb_0.5O₃ (BFN) ceramics were prepared by solid-state reaction method and were characterized by X-ray Diffraction (XRD) technique. Then, impedance spectroscopy measurements were conducted in a frequency range from 100 Hz to 1 MHz and in a temperature range from 293 to 600 K. Relaxation phenomena of non-Debye type have been observed in the BFN ceramics, as confirmed by the Cole–Cole plots. The higher values of ε′ at the lower frequencies are explained on the basis of the Maxwell–Wagner (MW) polarization model. Complex impedance analysis enables us to separate the contributions from grains and grain boundaries of our samples. We found that at higher temperatures grain boundary resistance is higher than grain resistance, irrespective of composition.     

Influence of frequency, temperature and composition on electrical properties of polycrystalline Co0.5CdxFe2.5−xO4 ferrites

Polycrystalline ferrites with general formula Co_0.5Cd_xFe_2.5−xO₄ (0.0?x?0.5) were prepared by sol-gel method. The dielectric properties ε′, ε″, loss tangent tan δ and ac conductivity σ_ac have been studied as a function of frequency, temperature and composition. The experimental results indicate that ε′, ε″, tan δ and σ_ac decrease as the frequency increases; whereas they increase as the temperature increases. These parameters are found to increase by increasing the concentration of Cd content up to x=0.2, after which they start to decrease with further increase in concentration of Cd ion. The dielectric properties and ac conductivity in studied samples have been explained on the basis of space charge polarization according to Maxwell and Wagner's two-layer model and the hoping between adjacent Fe²⁺ and Fe³⁺ as well as the hole hopping between Co³⁺and Co²⁺ ions at B-sites. The values of activation energies E_f for conduction process are determined from Arrhenius plots, and the variations in these activation energies as a function of Cd content are discussed. The complex impedance analysis is used to separate the grain and grain boundary of the system Co_0.5Cd_xFe_2.5−xO₄. The variations of both grain boundary and grain resistances with temperature and composition are evaluated in the frequency range 42 Hz-5 MHz.     

Anisotropic dielectric properties of PbYb1/2Ta1/2O3 single crystals

PbYb_1/2Ta_1/2O₃ single crystals were obtained for the first time. They were grown by the flux method. The PbOPbF₂B₂O₃ system was used as a solvent. Dielectric investigations were carried out in 1 0 0_c, 1 1 0_c and 1 1 1_c pseudocubic directions. These studies pointed to anisotropy of dielectric properties. Frequency-independent ε′(T) and ε″(T) maxima related to the antiferroelectric–paraelectric (AFE—PE) phase transition are observed for all directions at 562 K. The frequency-dependent ε′(T) and ε″(T) maxima near 400 K related to the ferroelectric (FE)–AFE phase transition are observed only in 1 1 1_c direction. The hysteresis loops were observed in this direction only. These results point that ferroelectric relaxor properties appear only in 1 1 1_c direction. We propose to consider the ferroelectric phase as ferrielectric one.     

Dielectric spectroscopy on Bi3Zn2Sb3O14 ceramic: an approach based on the complex impedance

The dielectric properties and loss of Bi_1.5ZnSb_1.5O₇ a poor-semiconducting ceramic were investigated by impedance spectroscopy, in the frequency range from 5 Hz to 13 MHz. Electric measurements were performed from 100 to 700 °C. Pyrochlore type phase was synthesized by the polymeric precursor method. Dense ceramic with 97% of the theoretical density was prepared by sintering via constant heating rate. The dielectric permittivity dependence as a function of frequency and temperature showed a strong dispersion at frequency lower than 10 kHz. The losses exhibit slight dependence with the frequency at low temperatures presenting a strong increase at temperatures higher than 400 °C. A decrease of the loss magnitude occurs with increasing frequency. Relaxation times were extracted using the dielectric functions Z″(ω) and M″(ω). The plots of the relaxation times τ_Z′ and τ_M″ as a function of temperature follow the Arrhenius law, where a single slope is observed with activation energy values equal to 1.38 and 1.37 eV, respectively.     

Immittance response of the SnO2-Bi2O3 based thick-films

The SnO₂-Bi₂O₃ based thick-film polycrystalline material is fabricated on alumina substrate via screen-printing technique. This material system is evaluated at various temperatures (35 °C≤T≤100 °C) using ac small-signal (immittance) measurements in the frequency range 10 Hz≤f≤10⁶ Hz. The simplistic analytical scenario for the immittance data employed the Cole-Cole empirical equation in conjunction with the estimation of the inspected input parameters. This is an alternate approach compared to the complex nonlinear least squares (CNLS) fitting procedure, and purely based on the appearance of the semicircular relaxation in the complex plane. It is found that the constituting components of the semicircular relaxation in the impedance plane are thermally activated indicating complexity in the grain boundary contributions despite the Debye and non-Debye relaxation responses. The possible degree of uniformity or non-uniformity in the grain boundary activity associated with its capacitance term observed via the Debye or non-Debye semicircular relaxation in the impedance (Z?) plane has been postulated.     

Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study

Impedance spectroscopy was used to study the oxygen reaction kinetics of La_0.8Sr_0.2MnO₃ (LSM)-based electrodes on Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes. Three types of electrodes were studied: pure LSM, LSM–YSZ composites, and LSM/LSM–YSZ bilayers. The electrodes were formed by spin coating and sintering on single-crystal YSZ substrates. Measurements were taken at temperatures ranging from 550 to 850°C and oxygen partial pressures from 1×10⁻³ to 1 atm. An arc whose resistance R_el had a high activation energy, E_a=1.61±0.05 eV, and a weak oxygen partial pressure dependence, (P_O2)^−1/6, was observed for the LSM electrodes. A similar arc was observed for LSM–YSZ electrodes, where R_el(P_O2)^−0.29 and the activation energy was 1.49±0.02 eV. The combination of a high activation energy and a weak P_O2 dependence was attributed to oxygen dissociation and adsorption rate-limiting steps for both types of electrodes. LSM–YSZ composite cathodes showed substantially lower overall interfacial resistance values than LSM, but exhibited an additional arc attributed to the resistance of YSZ grain boundaries within the LSM–YSZ. At 850°C and low P_O2, an additional arc was observed with size varying as (P_O2)^−0.80 for LSM and (P_O2)^−0.57 for LSM–YSZ, suggesting that diffusion had become an additional rate limiting step. Bilayer LSM/LSM–YSZ electrodes yielded results intermediate between LSM and LSM–YSZ. The results showed that most of the improvement in electrode performance was achieved for a LSM–YSZ layer only ≈2 μm thick. However, a decrease in the grain-boundary resistance would produce much better performance in thicker LSM–YSZ electrodes.     

Impedance spectroscopy study and ground state electronic properties of In(Mg1/2Ti1/2)O3

The complex perovskite oxide In(Mg_1/2Ti_1/2)O₃ (IMT) is synthesized by a solid state reaction technique. The X-ray diffraction of the sample at 30 °C shows a monoclinic phase. The dielectric properties of the sample are investigated in the temperature range from 143 to 373 K and in the frequency range from 580 Hz to 1 MHz using impedance spectroscopy. An analysis of the dielectric constant ε′ and loss tangent (tan δ) with frequency is performed assuming a distribution of relaxation times. The Cole-Cole model is used to explain the relaxation mechanism in IMT. The scaling behavior of imaginary part of electric modulus (M″) shows that the relaxation describes the same mechanism at various temperatures. The electronic structure and hence the ground state properties of IMT is studied by X-ray photoemission spectroscopy (XPS). The valence band XPS spectrum is compared with the electronic structure calculation. The electronic structure calculation indicates that the In-5s orbital introduces a significant density of states at the Fermi level, which is responsible for a high value of conductivity in IMT.     

Dielectric and AC conductivity behavior of BaBi2Nb2O9 ceramics

The complex dielectric and AC conductivity response of BaBi₂Nb₂O₉ relaxor ferroelectric ceramics were studied as a function of frequency (100 Hz-10 MHz) at various temperatures. The observed dielectric behavior was characterized by two types of relaxation processes which were described by the ‘universal relaxation law’. The frequency dependence of conductivity which showed a classical relaxor behavior followed the Jonscher's universal law σ(ω)=σ₀+Aωⁿ. The exponent n exhibited a minimum in the vicinity of temperatures of dielectric anomaly while the pre-factor A showed a maximum. The temperature dependence of n followed the Vogel-Fulcher relation with activation energy of about 0.14 eV.