Resistive Grain Research Articles

Lead-free (K0.5Na0.5)NbO3 co-substituted with Ta5+ and Er3+: Structural, optical, dielectric and electrical properties

The lead-free K0.5Na0.5NbO3 (KNN) ceramics co-substituted with 0.05 mol Ta5+ and x mol Er3+ ions (K, Na) (1-3x) ErxNb0.95Ta0.05O3, with x = 0.00 to 0.05, have been successfully manufactured by using the solid-state reaction. The XRD results showed that the ceramics crystalize in pure perovskite with a trace of secondary phase, for low Er levels (x ≤ 0.02). Above this rate, the presence of secondary phases became more significant. The optical band gap energy of the synthesis samples has been determined using UV–vis absorbance spectra using Tauc's relation. The Ta and Er co-substitution leads to decrease the Eg of KNN material. The grain size is found to be minimal ≈490 nm and 240 nm of sintered pellets at x = 0.02 and 0.05 of Er content respectively with a high density. The dielectric study of (K, Na) (1-3x) ErxNb0.95Ta0.05O3 ceramics was carried out and double peaks were observed in relative permittivity versus temperature data for pure KNN and KNNTa corresponding to orthorhombic-tetragonal-cubic phase transitions. While for Er doped-KNNTa samples only a broad ferroelectric-paraelectric phase transition is observed and it shifted to the high temperature with increasing Er content. This broad peak observed in dielectric data for x = 0.02 of Er content is due to inhomogeneity and will certainly open new applications in microwave dielectrics. The ac conductivity variation of KNErNTa ceramics with diverse Er concentration was analyzed according to the charge compensation mechanism. However, for KNNTa, a decrease in conductivity values is attributed to the reduction in leakage current density. Meanwhile, at x = 0.01 and 0.02 of Er concentration, Er-doped KNNTa became semi-conductor. Further investigation revealed that the resistance of grains and grains boundaries are both minimal for x = 0.02 sample which are responsible for the increase of ac conductivity. For high Er concentration ≥0.03, the RG and RGB values increase along with decrease of conductivity value related to the increase in grain size found in SEM micrographs.

Effects of SmCo Co-substitution on the magnetic and electrical properties of low temperature sintering synthesized strontium hexaferrite

In order to mitigate the rapid grain growth, a sintered ferrite magnet exhibiting stable characteristics was successfully synthesized. M-type strontium ferrite Sr1-xSmxFe12-xCoxO19 (x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05 and 0.10) was synthesized via a low-temperature co-firing method, incorporating an appropriate quantity of Bi2O3 and CuO as additives within the solid-phase reaction process. The magnetic and electrical properties of the resulting composites were meticulously examined, and X-ray diffraction (XRD) analysis was performed for structural characterization. The findings reveal that a pure hexagonal strontium phase is achieved consistently when the substitution level, x, remains below 0.5. With an increase in the substitution level, a heterogeneous phase α-Fe2O3 becomes apparent within the phase structure. Upon introducing doping elements, the subtle incorporation of SmCo (x ≤ 0.02) enhances the saturation magnetization, remanent magnetization, and coercivity of the composite material. Moreover, the resistances of grain and grain boundary (Rg, Rgb) have been downscaled from 1.856 × 106Ω and 3.61 × 106Ω to 3.182 × 104Ω and 4.37 × 105Ω respectively. Consequently, the Sr1-xSmxFe12-xCoxO19 ferrite sintered under low-temperature conditions demonstrates outstanding electromagnetic characteristics, presenting a viable option for materials in microwave device applications.

Structural, optical, and dielectric properties of M/SnO2 (M= Al2O3, NiO, Mn3O4) nanocomposites

The structural parameters, optical properties, and dielectric constants at a frequency (f) range of 0.1–20 MHz, and temperature (T) range of 300–400 K of hydrothermally synthesized M/SnO2 nanocomposites (for simplicity M denotes oxides of Al, Ni, or Mn) were compared. Rietveld refined X-ray powder diffraction (XRD) analysis demonstrated the formation of hexagonal, cubic, or spinel crystal structures of Al2O3, NiO, or Mn3O4 phases, respectively, besides the tetragonal rutile crystal structure of SnO2. The impact of Al addition on the optical band gap of SnO2 is negligible while it decreased or increased by incorporation of Ni or Mn, respectively. The residual lattice dielectric constant of SnO2 was increased, while the real part of the dielectric constant and the ac conductivity of SnO2 were decreased by M incorporation. The dielectric parameters are remarkably affected by selected M, T, and f values and their changes agree with the Maxwell-Wagner model. The Q-factor of SnO2 was increased by M addition while decreased with increasing T. The Ni/SnO2 obeys the hole conduction at T ≤ 330 K, while Mn/SnO2 and Ni/SnO2 obey the electronic conduction at T > 330 K. The binding energy is independent of the chosen T for SnO2, whereas it sharply increases for Ni/SnO2 and slightly decreases for Al/SnO2 and Mn/SnO2. The F-factor of SnO2 was slightly decreased by M addition, but it was increased with T for SnO2, Al/SnO2, and Mn/SnO2 while was decreased for Ni/SnO2. The Cole-Cole plots for M/SnO2 composites were analyzed, and the components of the equivalent circuit were determined. The electrical impedance, resistance of grains, resistance of grain boundaries, and equivalent resistance of SnO2 were increased by M incorporation, whereas equivalent capacitance was decreased. The findings recommend the SnO2-based nanocomposites for applications in optoelectronics, lithium batteries, supercapacitors, and solar cell devices.

Development and characterization of (1-x)BiYO3-xBiMnO3 ceramics for Ferro-photovoltaic applications

The rare combination of ferroelectricity, low band gap and high carrier mobility in a material can facilitate exceptional photovoltaic efficiency. In this paper, we attempted to reduce the band gap and improve the conductivity of ferroelectric solid solution BiY(1-x)MnxO3 by varying composition. The BiY(1-x)MnxO3 (x = 0.0, 0.10, 0.25, 0.50, 0.75) samples were prepared by high energy ball milling method and structural, dielectric, optical, electrical and ferroelectric properties were analyzed systematically. Herein, we show that band gap of the material is drastically reduced from 3.0 eV (BiYO3) to 1.76 eV (x = 0.50) and the samples exhibit ferroelectric behavior with significant polarization. Compound resistance of grain and grain boundaries were also found to reduce with increase in Mn concentration in the BiY(1-x)MnxO3 solid solution, demonstrating improvement in semiconducting behaviour of the material. Thus, solid solution formation of BiMnO3 with BiYO3, tunes band gap in useful region, improves electrical conduction and enhances ferroelectric polarization showing good potential for high performance solar cell and thermoelectric applications.

Band gap tunning to enhance photovoltaic response in NaNbO3-based bulk ferroelectrics

The observation of anomalous photovoltaic effect and switchable photocurrent in ferroelectrics receive extensive attention for its great advantages in next-generation high-performance photovoltaic devices, but the key factor, the wide band gap results in low photocurrent output and photoelectric conversion efficiency. Focusing on narrowing band gap to improve photovoltaic performance in NaNbO3, in this work, we fabricated the NaNbO3 and 0.8NaNbO3-0.2La(Mn0.5Ni0.5)O3 (abbreviated as 0.2NLMNO) ferroelectric ceramics through a solid state method. The optical absorption spectra reveal the band gap of ceramics reduce from 3.42 eV to 2.11 eV and the light absorption in visible region is significantly enhanced. A higher symmetry of crystal structure and great reduced resistance of grain and grain boundary induced by introducing La(Mn0.5Ni0.5)O3. What's more, the photocurrent density of 0.2NLMNO improves approximately 10 times larger than that of pure ferroelectric NaNbO3, it is expected to explore a new ferroelectric material with photovoltaic effect.

Structural, FTIR, optical and dielectric properties of Zn1-xAlxO ceramics for advanced applications

We report here the structural, FTIR, optical and dielectric properties of Zn1-xAlxO with x = 0.00 ≤ x ≤ 0.20)). The samples are synthesized by the solid state reaction method and the phase purity, structural morphology, and absorption spectra are examined by XRD, SEM, and FTIR techniques. The optical and dielectric measurements are obtained by a double beam spectrophotometer and an impedance analyzer. The wurtzite structure is confirmed for all samples, and the lattice parameters, crystallite diameter, and porosity are decreased by Al, whereas the Debye temperature and elastic modulus are increased. The residual stress is compressive for ZnO, but it is changed to tensile for the doped samples. Two different values of energy gap (Egh and Egl) are apparent for each sample. The Egh and Egl are, respectively, 3.60, 3.56, 3.43, 3.53, 3.68 eV and 3.02, 2.95, 2.85, 2.92, 3.07 eV for all samples such that ΔE = (Egh – Egl) ~ 0.60. The residual dielectric lattice constant is decreased by increasing x to 0.10, followed by a sharp increase at x = 0.20, while the opposite behavior is obtained for (N/m*). The dielectric constant and ac conductivity are slightly increased as x increases to 0.025, followed by a sharp increase with more increase of x to 0.20. The conduction is electronic for pure and x = 0.025 samples, but it changes to hole with increasing x to 0.20. The binding energy was decreased as x increased to 0.20, but there is no exact trend for the hopping distance and density of localized states against x. The F-factor for solar cell design was increased as x increased to 0.10, but it is almost constant at x = 0.20. The Cole–Cole plot is a straight line for x = 0.00, a semicircle arc for x = 0.025, and a complete semicircle for x ≥ 0.05. The impedance resistance of grain and grain boundaries decreases as x increases to 0.20. These outcomes indicate that the addition of Al to ZnO shifts the mechanical, optical, and dielectric medium to higher values, which is strongly recommended for the design of optoelectronic and solar cell instruments.

Electrical resistivity at the micron scale in a polycrystalline SiC ceramic

Grain boundaries typically dominate the electrical properties of polycrystalline ceramics. To understand the effect of grain boundaries on the electrical conductivity of SiC ceramics sintered with 2000 ppm Y2O3, the electrical resistivity of individual grains and multi-grains across boundaries at the micron scale was measured using a nano-probing system equipped with nano-manipulators. The results revealed that grain resistivity was bimodal because of the existence of a core/rim structure in grains, and the electrical resistivity of multigrain samples slowly increased with an increase in the number of grain boundaries crossed. Specifically, the electrical resistivity of a grain without a core, a grain with a core, a bicrystal with a single boundary, a sample crossing three boundaries, and a bulk polycrystalline sample were 2.36 × 10-1, 5.05 × 10-1, 4.80 × 10-1, 5.04 × 10-1, and 5.84 × 10-1 Ω cm, respectively. The results suggest that the electrical resistivity of polycrystalline SiC ceramics is primarily influenced by the presence of a grain boundary or core and secondarily by the number of boundaries.

The influence of ZrO2 doping on microstructure and electrical properties of ZnO-based conductive ceramics

ZnO-based conductive ceramic materials doping ZrO2 were prepared at 1320 °C by the conventional solid-state sintering method in air, and the influence of comprehensive properties with different ZrO2-doped content were studied carefully. Microstructure and crystals of the samples were investigated by SEM and XRD respectively. As a donor, Zr4+ increases the carrier concentration and decreases the resistivity of grain and grain boundary. As-prepared samples shown excellent linear V–I characteristics and were suitable for high frequency electric field. With the increasing of dopant ZrO2 contents, the dielectric constant and resistivity of ZnO-based conductive ceramics were influenced significantly, moreover, the resistance-temperature characteristics presents the negative temperature coefficient effects. ZnO-based conductive ceramics exhibited excellent comprehensive electrical performance with 0.30 mol% ZrO2-doping, in which the nonlinear coefficient is 1.01, the grain boundary barrier height is 0.014 eV, and the resistance temperature coefficient is −2.6×10−3/°C.

HANDY: a device for assessing resistance to mechanical crushing of maize kernel

BackgroundHow to control the physical damage during maize kernel harvesting is a major problem for both mechanical designers and plant breeders. A limitation of addressing this problem is lacking a reliable method for assessing the relation between kernel damage susceptibility and threshing quality. The design, construction, and testing of a portable tool called “HANDY”, which can assess the resistance to mechanical crushing in maize kernel. HANDY can impact the kernel with a special accelerator at a given rotating speed and then cause measurable damage to the kernel. These factors are varied to determine the ideal parameters for operating the HANDY.ResultsBreakage index (BI, target index of HANDY), decreased as the moisture content of kernel increased or the rotating speed decreased within the tested range. Furthermore, the HANDY exhibited a greater sensitivity in testing kernels at higher moisture level influence on the susceptibility of damage kernel than that in Breakage Susceptibility tests, particularly when the centrifugation speed is about 1800 r/min and the centrifugal disc type is curved. Considering that the mechanical properties of kernels vary greatly as the moisture content changes, a subsection linear (average goodness of fit is 0.9) to predict the threshing quality is built by piecewise function analysis, which is divided by kernel moisture. Specifically, threshing quality is regarded as a function of the measured result of the HANDY. Five maize cultivars are identified with higher damage resistance among 21 tested candidate varieties.ConclusionsThe HANDY provides a quantitative assessment of the mechanical crushing resistance of maize kernel. The BI is demonstrated to be a more robust index than breakage susceptibility (BS) when evaluating threshing quality in harvesting in terms of both reliability and accuracy. This study also offers a new perspective for evaluating the mechanical crushing resistance of grains and provides technical support for breeding and screening maize varieties that are suitable for mechanical harvesting.

Electrical conduction mechanism of barium doped strontium hydroxyapatite synthesized by co – precipitation method

The crystalline samples of Barium (Ba) doped Sr10-xBax(PO4)6(OH)2 with x = 0, 0.5 and 1 mol% were prepared by co – precipitation method. The microstructural (SEM) image shows the distribution of densely packed grains over the surface of prepared sample. The nature of cole – cole plots confirm that the conduction mechanism is governed only by the grains with no contribution of grain boundaries for all prepared samples. The resistance of grains decreases with increase in temperature and molar (mol%) concentration, which shows a negative temperature coefficient resistance (NTCR) behaviour for all prepared samples. The a.c. conductivity increases with increase in frequency which shows non – debye nature of the prepared samples.

Breeding of highly productive varieties of winter triticale resistant to pre-harvest germination of grain in the ear

Creation of new varieties of winter hexaploid triticale for the central part of Russia is characterized by increased resistance of grain to germination on the root. The phenomenon of germination on the root is one of the limiting traits that limit the spread of triticale culture in areas of excessive moisture, which is the Central Region of the Non-Chernozem zone. The work was carried out at the Russian State Agrarian University – Moscow Agricultural Academy named after K.A. Timiryazev in 2018-2019. Field experiments were conducted in the fields of the Field Experimental and Breeding Stations. Laboratory tests were carried out at the Department of Genetics, Breeding and Seed Production. As a result of a comprehensive assessment of breeding varieties in the preliminary variety testing, the most valuable sample of winter triticale 228h (Castus x Don) was isolated, which formed a yield at the standard level, and during 3 years of study showed relatively high resistance to pre-harvest germination of grain in the ear. This sample is currently being intensively propagated for transfer to the State Variety Testing in 2020.

Investigation of electrical conduction in Ca6-xNa2Y2(SiO4)6F2:xEu3+ ceramic by complex impedance and electric modulus spectroscopy

The electrical conduction mechanism of Ca6-xNa2Y2(SiO4)6F2:xEu3+ fluorapatite ceramic with (x = 0–0.05 mol%) synthesized by solution combustion method has been investigated by dielectric, complex impedance and electric modulus spectroscopy. Microstructural analysis was carried out by scanning electron microscopy (SEM) which shows that the spheroidal and ellipsoidal grains were distributed uniformly in the prepared ceramic with average grain size of the order of 3 μm. The electrical and dielectric studies of the ceramic were done in the frequency range of 100 Hz–100 KHz and temperature range of 50 °C–500 °C. The temperature and frequency dependent dielectric loss and dielectric constant decreases with an increase in frequency due to the ceasing effect of polarization. Dielectric relaxation behaviour of the prepared ceramics were studied using Complex impedance spectroscopy (CIS). Nyquist plots show that with increase in Eu3+ ion concentration the resistance of grains and grain boundaries decreases for the prepared ceramics. The investigation of charge transport phenomena was done by electric modulus spectroscopy. The drastic increase in a. c conductivity with increase in temperature shows that the ceramic follow the Jonscher’s power law and appear Debye in nature.

Effect of sintering temperature on spark plasma sintered PbZr0.52Ti0.48O3: Impedance and energy storage analysis

In the present work, the phase analysis, different relaxation mechanisms, dominant conduction mechanism and energy storage performance of spark plasma sintered PbZr0.52Ti0.48O3 (PZT) material at different temperatures (800, 850, 900, and 950 °C) are presented. The XRD analysis indicates difference in phase constitution of the synthesized PZT ceramics in which the sample sintered at 900 °C and 950 °C showed presence of multiple phases. Impedance and electric modulus studies are conducted on the samples over the frequency range 0.01 Hz–1 MHz at room temperature. The analysis revealed approximated Debye type behaviour for low frequency relaxation process in all the samples. The separation of grain and grain boundary relaxation process are observed in the frequency dependent imaginary electrical modulus M″ plots and complex modulus spectra rather than in Bode plots and Nyquist plots. Such contrast was attributed to high resistance and low capacitance of the bulk contribution. Complex impedance measurements, thereby estimating ac conductivity and electric modulus have established a distinctive feature for the PZT spark plasma sintered at 900 °C. The resultant electrical properties of the materials are analyzed through understanding the grain and grain boundary relaxation mechanisms and drawing a possible connection with crystal structures of the sintered materials. PZT sintered at 900 °C, as compared to other counterparts, has shown unique combination of tetragonal and monoclinic crystal structures of constituent phases which exhibits highest impedance and electrical modulus among the samples. The resistances of grain and grain boundary of sample sintered at 900 °C are found to be 1.06 × 105 Ω and 5.80 × 108 Ω respectively. The saturation polarization 17.32 μC/cm2 and the coercive field 5.92 kV/cm of the sample are also found highest and lowest respectively for the 900 °C sintered sample among all the samples studied. The energy storage efficiency of the PZT sintered at 900 °C is also highest ~66.38%.

Zn-Doped Calcium Copper Titanate Synthesized via Rapid Laser Sintering of Sol-Gel Derived Precursors.

Zn-doped calcium copper titanate (CCTO) was successfully synthesized by rapid laser sintering of sol-gel derived precursors without the conventional long-time heat treatment. The structural, morphological, and crystalline properties were characterized, and the performances of dielectrics and impedance were measured and discussed. The X-ray diffractometer results show that Zn-doped CCTO is polycrystalline in a cubic structure, according to the doping ratio of Ca(Cu2Zn)Ti4O12. Electron microscopy showed that Zn-doped CCTO has a denser microstructure with better uniformness with shrunken interplanar spacing of 2.598 nm for the plane (220). Comparing with undoped CCTO, the permittivity almost remains unchanged in the range of 102–106 Hz, demonstrating good stability on frequency. The electrical mechanism was investigated and is discussed through the impedance spectroscopy analysis. The resistance of grain and grain boundary decreases with rising temperature. Activation energies for the grain boundaries for Zn- doped CCTO were calculated from the slope for the relationship of ln versus 1/T and were found to be 0.605 eV, smaller than undoped CCTO. This synthesis route may be an efficient and convenient approach to limit excessive waste of resources.

Giant permittivity up to 100 MHz in La and Nb co‐doped rutile TiO2 ceramics

AbstractDielectric spectroscopy was carried out for reduced and stoichiometric La0.0025Nb0.0025Ti0.995O2 ceramics synthesized by sintering in different atmospheres. A giant permittivity (~1 × 104) was obtained at a frequency of 100 MHz and temperature range from 170 to 350 K. Three dielectric relaxation mechanisms were observed within the temperature range of 10‐300 K via dielectric spectroscopy. A low temperature dipole relaxation peak (in the temperature range of 10‐30 K) in the spectra was identified to be associated with the giant permittivity specifically measured at 100 MHz. The origin of such giant permittivity was attributed to dipole orientation polarization. Hopping polaron and interfacial effect contributed to giant permittivity. After annealing treatment, all the relaxation contributions were weakened. Low dielectric loss was attributed to high resistance of grain and grain boundaries. Annealing in ambient conditions led to decreased relaxation times which gives the signature of decreased concentration of oxygen vacancies and Ti3+. Dipoles which were related to oxygen vacancies and Ti3+, resulted in giant permittivity up to 100 MHz.

Dielectric and thermal behavior of 0.75BiFeO3-0.25BaTiO3 filled ethylene vinyl acetate composites

Bismuth ferrite-Barium Titanate (BFO-BT) filled ethylene-vinyl acetate copolymer (EVA) composites have been processed by solution casting technique followed by compression molding. The effects of BFO-BT on structural, thermal and dielectric behaviour of the composites have been investigated using X-ray diffraction, field emission scanning electron microscopy, thermal analysis (DSC, TGA) and impedance analyser. As analysed by XRD and DSC analysis, with increase in BFO-BT content the crystallinity of EVA matrix decreases. BFO-BT has great effect on higher thermal stability of the composites. EVA/BFO-BT composites exhibit significantly enhanced relative dielectric permittivity (εr = 182) near the percolation limit of about 30 phr BFO-BT loading at 25 °C and 1 kHz frequency. With 30 phr BFO-BT loading, the dielectric loss of the composite shows only an approximately 2-fold increase i.e., from 0.04 to 0.091. The capacitance and resistance of grains is found from the exploratory Nyquist plots with the assistance of an electrical circuit. A cautious examination of the experimental complex impedance plots and model fitted plots is contemplated which fulfilled the precision of the information tentatively. With enhanced dielectric properties and thermal stability, the BFO-BT filled EVA composite system can be used for solar cells and energy saving devices.

The electronics transport mechanism of grain and grain boundary in semiconductive hafnium oxynitride thin film

HfOxNy thin film was deposited on oxidized silicon substrate; its physical structure and chemical composition were studied in detail by X-ray diffractometer, scanning electron microscopy, field emission transmission electron microscope and X-ray photoelectron spectrometer. Microtemperature sensors with high sensitivity based on the film were fabricated. To clarify the conduction process of grain, grain boundary (GB) and the whole film, temperature-dependent AC impedances of a sensor were measured and analyzed in 40–300 K. The results show that at all of the measured temperatures, the resistance of grain is much larger than that of GB, and its rising rates with the temperature reduction are also much larger than that of GB, indicating that the resistive property of HfOxNy thin film is determined by grain. In addition, it has been confirmed that the conduction process of both the HfOxNy film and GB is dominated by thermal activation and Mott variable-range hopping (VRH) in relatively high and low temperature range, respectively. The conduction process of the grain obeys Mott VRH in the whole considered temperature range, while the Mott characteristic temperature is changed. These results provide new insights into the performance enhancement of the transition metal oxynitride-based temperature sensors.

Impedance studies of K0.5Na0.5NbO3 ceramics prepared from mechanochemically activated powders

Recently worldwide environmental considerations demand the elimination of lead-based materials from all consumer items. Potassium sodium niobate solid solution seems to be one of the most promising candidate to replace the PZT-based ceramics in piezoelectric devices. In this paper the K1/2Na1/2NbO3 ceramics have been obtained from mechanochemically activated powders containing the stoichiometric ratio of niobium oxide, potassium and sodium carbonates. The activation process occurred in a high energy mill (shaker type), for different periods between 25 h and 100 h. The sintered ceramic samples, prepared from mechanochemically activated powders, have been investigated by XRD, SEM and impedance studies in order to determine the influence of mechanochemical process on the final ceramic properties. The ceramic properties have showed a strong correlation with the milling duration. Based on the performed investigations it is possible to distinguish between the material response related to the grains and the grain boundaries. The resistance of grains and grain boundaries increases with the high energy milling time. The similar trend has been recorded in case of capacitance. Moreover, the anomaly, related to the ferroelectric-paraelectric phase transition, is visible on both temperature dependencies of grains and grain boundaries capacitances.

THERMAL EXPANSION, ELECTROTRANSPORT AND DIELECTRICAL PROPERTIES OF Bi4(Ti,Nb,Fe)3O12 SOLID SOLUTIONS

The Bi4Ti3–2xNbxFexO12 (0.05 ≤ x ≤ 0.15) titanates were prepared using ceramic method. Their structure and physicochemical properties were studied. Compounds were p-type semiconductors, which electrical conductivity, Curie temperature, dielectric constant, and dielectric losses decreased, but lattice constants, thermo-EMF coefficient and sinterability did not changed at partial replacing of titanium by niobium and iron. Introduction of niobium and iron oxides into ceramics based on layered Bi4Ti3O12 lead to the sharp decreasing in its grains size. The transition of ceramics from ferroelectric to paraelectric state was accompanied by a stepwise increase in linear thermal expansion coefficient (LTEC) (from (9.63–9.81)·10–6 K–1 to (12.71-14.67)·10–6 K–1 and by decrease in the activation energy of DC electrical conductivity (from 1.13–1.52 eV to 0.72–0.99 eV). Electrical resistivity of ceramics was determined by electrical resistivity of grains, relaxation processes in it were of a non-Debay type, while the activation energy of relaxation for Bi4Ti3–2xNbxFexO12 titanates, found from impedance spectroscopy (1.01–1.05 eV), was close to the value activation energy of their intragrain conductivity (0.85–0.97 eV). The frequency dependences of AC electrical conductivity obeyed Jonscher’s power law σ ~ νn, where n < 1 and increased with temperature, which indicated that charge transfer in the ceramic was accomplished by ions translating over small distances, which was accompanied by small polarons hopping charge transfer.

Impedance spectroscopy studies on samarium and sodium substituted strontium bismuth titanate (SBTi)

Abstract Sr 1-x Sm x Na x Bi 4 Ti 4 O 15 lead-free piezoelectric ceramics are prepared by solid-state sintering method using high energy Ball- Mill and ground for 10 h. The single phase of the compound is confirmed by X-ray Diffraction and highest intensity peak (1 1 0) is observed at 30°. Diffraction peaks shifted towards higher angles with an increasing concentration of Sm 3+ and Na 1+ of SBT. Grains orientation and grain size are analyzed by Scanning Electron Microscope. Temperature and frequency dependent AC conductivity studies are carried out using impedance spectroscopy in the temperature range of 30 °C–650 °C using Wayn-Kerr LCR meter. At lower frequencies, conductivity is independent of frequency. The variation of Z″ with frequency shows peaks shifting towards higher frequencies with an increase of temperature. The resistance of grains (R g ), grain boundaries (R gb ) are calculated and it is found that grain resistance is greater than grain boundary resistance (R g > R gb ). Relaxation times of grain and grain boundaries are calculated.