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AlN ceramics exhibit good physical and chemical properties and are ideal materials for the dielectric layer of electrostatic chucks. However, they cannot generate a strong J−R-type electrostatic adsorption force because of their high resistivity. Therefore, adding other substances is necessary to regulate the electrical properties and enable their application. In this study, AlN ceramics were prepared using hot-pressed sintering with 0.2 wt% CaO as an additive at a sintering temperature range of 1700–1900 °C. The effects of CaO doping on the phase composition, microstructure, electrical properties, and thermal conductivity of the AlN ceramics were systematically investigated. The addition of CaO not only enhanced the sintering process of the AlN ceramics, but also significantly reduced the electrical resistivity and increased the thermal conductivity. The relative density of CaO-doped AlN ceramics reached 98.88 % at 1700 °C, with a thermal conductivity of 81.51 W m−1•K−1. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and AC impedance spectroscopy were used to analyse the impurities and defects in the AlN ceramics. The lattice parameters and fitting grain resistance indicated that the CaO-doped AlN presented a higher lattice oxygen concentration, increasing the concentration of Al vacancies and electrons. Moreover, the level of dissolved oxygen could be controlled by altering the sintering temperature, resulting in AlN ceramics with electrical resistivity ranging from 8.1 × 106 to 1.7 × 1012 Ω cm. Further research was conducted to investigate the effect of the electrical resistivity of AlN ceramics on the J−R-type electrostatic adsorption force, and it was found that AlN ceramics with a specific resistivity of 109 Ω cm exhibited the highest electrostatic adsorption of 351.7 g/cm2. [ABSTRACT FROM AUTHOR]

In the present work, the Sr(Fe0.5Nb0.5)1-xMnxO3 powders were synthesized via a molten salt technique. Pure phase perovskite was obtained at 800 °C which was very low compared to previous works prepared by solid state reaction technique (> 1200 °C). XRD analysis for the Sr(Fe0.5Nb0.5)1-xMnxO3 ceramics revealed that the unit cell had an orthorhombic symmetry. Examination of dielectric measurement showed that all ceramic samples exhibited very high dielectric constants (εr,max > 200,000 at 1 kHz). The dielectric data showed that all ceramics exhibited a relaxor like behavior. Loss tangent value tended to decrease with increasing Mn, especially at low temperature range. The obtained loss tangent values were found to be lower than those reported in previous works. Impedance spectroscopy analysis revealed that the relaxor like behavior could be related with bulk grain, grain boundaries and electrode responses, where the samples had a heterogeneous conduction. Type of electrode and applied voltage had strong effects on the dielectric behavior. [ABSTRACT FROM AUTHOR]

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) Mn x O 3 by varying composition. The BiY (1-x) Mn x O 3 (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 (BiYO 3) 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) Mn x O 3 solid solution, demonstrating improvement in semiconducting behaviour of the material. Thus, solid solution formation of BiMnO 3 with BiYO 3 , tunes band gap in useful region, improves electrical conduction and enhances ferroelectric polarization showing good potential for high performance solar cell and thermoelectric applications. [ABSTRACT FROM AUTHOR]

In this study, 0.5Ca 0.15 Sr 1.85 Bi 4 Ti 5 O 18 (CSBT)-0.5BiFeO 3 (BFO) ceramics were synthesized, and the effects of different sintering atmospheres (air and N 2) on their structure and electrical conductivity were reported. According to XRD, TEM, and Raman analyses, the 0.5CSBT-0.5BFO ceramics had a B2cb space group (orthorhombic crystal structure) and an m=5 bismuth layered perovskite structure, except the Bi 2 O 3 second phase (cubic, Pn-3m) is in the air-sintered sample. The XPS analysis results show that the air-sintered sample had a greater hole (h •) concentration than the N 2 -sintered sample. The impedance and conductivity investigation results show that the 0.5CSBT-0.5BFO ceramics had p-type and CBH conduction mechanisms. [ABSTRACT FROM AUTHOR]

Mullite ceramics of two different compositions Al 0·60 Si 0·40 O and Al 0·75 Si 0·25 O have been synthesized by pyrophoric method followed by reaction sintering at 1050°C. The structural, micro-structural, optical, and dielectric characterization of mullite has been carried out through XRD, Raman, SEM, UV–Visible and dielectric studies. In this work, the synthesized mullite materials possess quite high dielectric constant value with negligible dielectric loss factor. The room temperature dielectric constant values for Al 0·60 Si 0·40 O and Al 0·75 Si 0·25 O stoichiometric mullites are found to be 110 and 2665 with a loss factor of 2.04 and 2.29 at 100 Hz frequency, which is comparatively high than the corresponding values of dielectric constants reported in previous literatures of mullite. The dielectric constant values for both the ceramics are very high (>104) for temperatures greater than 250°C. The room temperature dielectric constant (6.03 and 5.08, at 1 MHz), dielectric loss (0.07 and 0.05, at 1 MHz), electrical conductivity (1.5 × 10−5 S/m and 8.1 × 10−6 S/m, at 300 °C) results for Al 0·60 Si 0·40 O and Al 0·75 Si 0·25 O prove these ceramics suitable for electronics-related applications. The Arrhenius type conductivity, non-Debye type relaxation mechanism is confirmed from AC conductivity, complex impedance, and modulus study of these ceramics. These ceramics possess high optical band gap values of 3.46 eV and 3.36 eV for Al 0·60 Si 0·40 O and Al 0·75 Si 0·25 O, respectively which is suitable for using as electronic circuit packaging material or as a dielectric substrate material for any kind of storage devices. [ABSTRACT FROM AUTHOR]

In this study, the intermediate rare-earth oxide Gd 2 O 3 (Gd) was substituted in different amounts (x = 0.2–2 mol%) for the formulation of BaTi 1-x Gd x O 3-x/2 (BTG x) dielectric materials. The effect of B-site substitution was confirmed by the additional Raman active A 1g octahedral peak at ~835cm-1 strengthened at x ≥ 0.4 mol%. Additionally, properties of 0.9BTG 0.007 -0.1BA dielectric ceramics were analysed based on the influence of various processing methods as a function of sintering temperature. The focal samples were labelled Method-A (direct-mix) and Method-B (indirect-mix). As the sintering temperature (1075–1200 °C) increased, the 1 kHz response of the ε–T curves of Method-A samples transformed from a single peak to broad-narrow double peaks of high dielectric loss tangent (tan δ). Nonetheless, samples of Method-B possessed a clearly defined transmission electron microscopy (TEM) core-shell structure, flattened double-peak ε-T curves, optimised dielectric properties (ε = ~1563–1851 and tan δ < 1.5% at room temperature), and a wide-ranging temperature behaviour that meets the X8R dielectric standards (ΔC/C 25°C < ±15%). The maximum dielectric breakdown strength of Method-B samples reached ~131 kVcm, while the energy storage density was ~0.726 J/cm3 at a maximum efficiency of ~80% at 1100 °C. Thus, exhibiting good potentials for balancing temperature stability with energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

This study explores the influence of processing methods on the connectivity of a ceramic component and its effect on the dielectric and thermal properties in Li 2 MoO 4 -polytetrafluoroethylene (LMO-PTFE) composites. Three processing cases were examined: cold sintering (case 1), dry pressing and subsequent thermal annealing (case 2), and cold sintering and subsequent thermal annealing (case 3). The processing methods change the connectivity of ceramic grains, the crystallinity of PTFE, and the dielectric properties of these composites. The microstructure analysis shows that CSP increases the LMO domain size via the dissolution and precipitation steps. The connected LMO grains increases the transport length of Li ions under electric field and manifests the space charge polarization in the dielectric measurments. More connected LMO grains of the composites also enhance thermal transport, while phonon scattering of discrete LMO particles lowers the thermal conductivity of the composites. • Processing methods change the connectivity of a ceramic component in a polymer matrix. • Cold sintering process increases the ceramic domain size in the ceramic-polymer composite. • The connected ceramics grains increase the transport length of Li ions under electric field. • Thermal conductivity can be enhanced by a chain of connected ceramic grains. • This study contributes to the rational design of high-performance dielectric composites. [ABSTRACT FROM AUTHOR]

Multiferroic composites with general formula Ba(Ti0.95Zr0.05)O3 – Ni0.7Zn0.3Fe2O4, Ba(Ti0.95Zr0.05)O3 – CoFe2O4, Ba(Ti0.95Zr0.05)O3 – Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4, (BTZr(95–5) – NZF, BTZr(95–5) – CF, BTZr(95–5) – NCuSmZF) were prepared by mixing chemically obtained different types of ferrites and BTZ(95–5) powders in the planetary mill for 24 h. The optimization of sintering process was performed and powders were pressed and sintered at 1300 °C for obtained composites samples. From the X-ray analysis for single phase and composites ceramics the formation of crystallized structure of ferrites and barium zirconium titanate can be noticed. SEM analyses indicated the formation of two types nanosized grains, polygonal ferromagnetic and rounded ferroelectric grains. The electrical properties of these materials were investigated using impedance spectroscopy and analysis of ferroelectric measurements. Impedance analysis of all investigated samples has shown different relaxation processes that originated from the grain and grain boundary contributions. The results of polarization vs. electric field measurements have shown the influence of magnetic phase type and its concentration on the ferroelectric properties of the composites. Due to high conductivity of ferrite phases and presence of interfacial polarization, the shapes of these curves differed from the conventional ferroelectric materials. [ABSTRACT FROM AUTHOR]

LaFe 1 − x Zn x O3 (x = 0.03, 0.05, and 0.07) ceramics were prepared in two steps: preparation of the powder form by a sol–gel method followed by sintering-annealing treatments to form the bulk-phase. X-ray diffraction analysis revealed that all ceramics were crystallized in the orthorhombic perovskite structure with Pbnm symmetry. Grain size distribution and morphological characteristics were investigated by scanning electron microscopy. Specific surface area was analyzed through BET–BJH methods. Electrical impedance analysis was investigated as a function of frequency at various temperatures. It was found that the electrical behavior is dominated by grain boundary contribution, i.e., electrical conductivity. The frequency dependence of the complex conductivity was analyzed through Joncher's power law and the dominance of translational motion with a sudden hopping mechanism in the electrical conduction mechanism increased with increasing Zn content. Activation energy decreased with increasing Zn content. [ABSTRACT FROM AUTHOR]

The (La 1/2 Ta 1/2) x Ti 1-x O 2 and (Er 1/2 Ta 1/2) x Ti 1-x O 2 ceramics with x = 0.01 and 0.03 were synthesized by a conventional solid-state reaction. The analysis of EDS mapping, ac conductivity spectra, impedance analysis, XPS, and DC bias indicate that electrons-pinned defect-dipole (EPPD) polarization plays the main role in both the (La 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 and (Er 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 ceramics, while the interfacial polarization and hopping polarization are respectively highlighted by the (La 1/2 Ta 1/2) 0.03 Ti 0.97 O 2 and (Er 1/2 Ta 1/2) 0.03 Ti 0.97 O 2 ceramics. Besides, the dielectric responses reveals that the interfacial polarization and hopping polarization are much slower than EPDD polarization and lead to poor frequency-, temperature-stability and higher dielectric loss (tanδ). Then the conclusion can be drawn that the outstanding dielectric properties can be achieved only the EPDD polarization takes the absolute dominant position, and excellent properties are obtained in (Er 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 ceramic with ultra-low loss of tanδ≈0.0095 (@1 kHz) and excellent frequency, temperature and DC bias stability. • In this work, the effects of different polarizations on the CP TiO 2 systems are revealed and concretely discussed. • The dielectric properties of LTTO and ETTO ceramics with x=0.01 and 0.03 are systematically studied. • The 1% ETTO and 1% LTTO ceramics with ultralow dielectric loss (1%ETTO: tanδ≈0.0095; 1%LTTO: tanδ≈0.0155 at 1kHz). [ABSTRACT FROM AUTHOR]

Abstract Aurivillius single-phase Bi 2.5 Nd 0.5 Nb 1.5 Fe 0.5 O 9 (BNNF) ceramics was synthesized via solid state mixed oxide sintering method. Electrical properties of the samples were intensely studied in a wide range of temperature (25 °C–650 °C). Dielectric behaviors were investigated by dielectric and impedance spectroscopies in the range (40 Hz−10 MHz) of frequency. Single dielectric relaxation was observed due to the grains contribution. The phase transition temperature (T C) was noticed at ∼270 °C. Kinetic analysis of dielectric data was used to understand the possible relaxation-conduction behaviors in the ceramics. Above ∼250 °C, relaxation and conduction of the ceramics was assigned to the motion of ionized oxygen vacancies. The Aurivillius ceramics has promising industrial applications in dielectric capacitors and piezoelectric transducers due to low leakage below ∼200 °C. The results could be valuable for designing and/or modifying properties of BNNF related materials. Highlights • Aurivillius Bi 2.5 Nd 0.5 Nb 1.5 Fe 0.5 O 9 ceramics was synthesized for the first time. • A ferroelectric transition was observed at ∼270 °C. • Single dielectric relaxation was observed due to grains contribution. • Above ∼250 °C conduction and relaxation was due to ionized oxygen vacancies. [ABSTRACT FROM AUTHOR]

A series of (BaO)x-(ZnO)1-x-TiO2 (x = 0.1-0.9) ceramic materials were synthesized via the conventional solid-state reaction method and finally sintered at 1200 °C. The diffraction pattern revealed that the cubic (Zn2Ti3O8 and BaTiO3) and monoclinic (Ba2ZnTi5O13) phases were present in the resultant compositions. The morphology was analysed using scanning electron microscope. The presence of metal oxide (M-O) stretching vibrations was confirmed by Fourier transform infrared spectra. The AC electrical properties such as dielectric constant (εr), loss tangent (tan δ) and AC conductivity (σac) were investigated as a function of temperature (313-673 K) and frequency (100 Hz-5 MHz). The high dielectric constant and loss values were obtained for higher barium contents (beyond x = 0.5) owing to the presence of smaller number of monoclinic Ba2ZnTi5O13 phases. The effect of space-charge polarization was explained from dielectric modulus (M′ and M″) behaviour. The Nyquist plots (Z′ versus Z″) were drawn to justify the electrical conduction mechanism of all compositions. The bulk resistances (Rb) were calculated from Nyquist plots. The room temperature ferroelectric behaviour was illustrated with the help of P-E loop tracer. [ABSTRACT FROM AUTHOR]

Single-phase Aurivillius Bi 4 Nd 0.5 Gd 0.5 Ti 3 FeO 15 ceramics was synthesized via the solid-state reaction technique. Rietveld refinement of the full XRD pattern was carried out to obtain the detailed structure of the compound. Dielectric response and electrical properties of the ceramics were investigated in a wide range of frequency and temperature by dielectric/impedance spectroscopies. Two dielectric relaxations were distinguished, which were attributed to grains and grain boundaries respectively, by the combination of impedance and modulus analysis. Resistance of grain boundaries was determined much larger than that of grains. The kinetic analysis of temperature dependent dielectric data was performed to study the corresponding relaxation-conduction behaviors in the material. The thermal magnetization measurement evidenced the paramagnetic characteristic of the material, but localized antiferromagentic coupling would exist below 200 K. In addition, a phase transition was observed at ~240 °C. [ABSTRACT FROM AUTHOR]

Aurivillius single-phase Bi 3.5 La 0.5 Ti 2 Nb 0.5 Fe 0.5 O 12 ceramics was synthesized by solid state reaction route. The ac data in terms of dielectric and impedance were collected to probe the dielectric relaxation behaviors in the ceramics. Two relaxations were distinguished and determined to originate from grains and grain boundaries, respectively, by the combination of impedance and electric modulus analysis. A phase transition was observed to take place at ∼440 °C. The possible relaxation-conduction mechanisms were discussed on the basis of kinetic analyses of dielectric data. This work elucidated the contributions of microstructures and defects to the relaxations and conduction. It is significant for correct understanding of electrical properties of Bi 3.5 La 0.5 Ti 2 Nb 0.5 Fe 0.5 O 12 related ceramics and consequent modification of process to improve the performance of ceramics. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) is considered as a potential candidate for clean and efficient alternate energy source. Efforts are being made to reduce their operating temperature for SOFCs commercialization. However, the reduction in operating temperature increases the polarization effect in the existing cathodes. In the present study, Bi0.5Sr0.5MnO3was synthesized and studied for its structural, thermal, and electrical properties. Bi0.5Sr0.5MnO3was synthesized by conventional solid state reaction method. The as-prepared sample was characterized by x-ray diffraction, scanning electron microscope, thermogravimetric analysis, dilatometer and impedance spectroscopy. The Rietveld refinement results confirm that Bi0.50Sr0.50MnO3shows the tetragonal symmetry withp4 mmspace group. Scanning electron microscopy study shows that the distribution of grains is uniform and the grains are well connected to each other due to better sinterability of the samples. The dilatometric curve shows linear behavior up to 600°C and after that becomes steeper. This can be due to the loss of lattice oxygen at higher temperatures and creation of oxygen vacancies. The thermal expansion coefficient of the system is ∼8.9 × 10−6°C−1and total conductivity of the sample is ∼4.78 × 10−3 S/cm. [ABSTRACT FROM AUTHOR]

Scaling behavior and conduction mechanism of lead-free BaZr 0.1 Ti 0.9 O 3 (BZT) dielectric ceramic is studied at the elevated temperatures between 400 to 540 ° C. Single-phase with tetragonal BZT ceramic P4 mm is formed. The XPS analysis confirms the Zr-doping at the Ti-site. Conductivity phenomena confirm that the conduction process of charge carriers is governed by oxygen vacancies at all temperatures. Impedance analysis shows a decrement in the impedance with the increase in temperature. Nyquist analysis reveals the decrease in grain and grain boundary resistances at higher temperatures. Non-Debye type behavior is confirmed by the Modulus spectroscopy and normalized master curves of electrical modulus confirm existence of the same conduction mechanism at all the temperatures. The scaling behavior of the BZT ceramic shows that conduction mechanism shifts from the long-range mobility of the charge carriers towards short-range mobility with increasing frequencies due to thermal agitation at elevated temperatures. • Zr substituted barium titanate ceramic is successfully prepared with tetragonal phase • The conduction process of charge carriers is mainly governed by oxygen vacancies • Non-Debye type behavior is confirmed for all the temperatures by Modulus spectroscopy • Normalized master curves of M ′ ′ confirm same conduction mechanism at all temperatures • The scaling behavior of the BZT ceramic shows that the conduction mechanism shifts from the long-range mobility of the charge carriers towards the short-range mobility with increasing frequencies due to thermal agitation at elevated temperatures. [ABSTRACT FROM AUTHOR]

The polycrystalline sample of a new tungsten bronze ferroelectric vanadate, Li2Pb2La2W2Ti4V4O30, was prepared at a relatively low temperature using a mixed-oxide technique. The formation of the material under the reported conditions has been confirmed by an X-ray diffraction technique. A preliminary structural analysis exhibits orthorhombic crystal structure of the material at room temperature. Studies of dielectric properties (ϵ, tanδ) of the above compound as a function of temperature (273–600K) at frequencies 10, 100, 1000 KHz exhibits a ferroelectric phase transition of diffuse type. The electrical properties of the material have been studied using ac impedance spectroscopy technique. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The temperature dependence of electrical relaxation phenomenon in the materials has been observed. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR) –type behavior similar to that of semiconductors. A small contribution of grain boundary effect was also observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The ac conductivity spectra exhibit a typical signature of an ionic conducting system, and are found to obey Jonscher's universal power law. [ABSTRACT FROM PUBLISHER]

Various commercially available anode and cathode materials are investigated as the anode and cathode contact paste, respectively, for solid oxide fuel cells. In order to obtain a printable paste, chosen materials are mixed with an organic vehicle and a thinner as well as a pore former. The effect of the contact materials on the cell performance is evaluated experimentally via cell performance measurements by installing a short stack. The pastes are brush painted on the corresponding interconnector and current collecting mesh. A short stack without any contact paste is also tested for comparison as a base case. The impedance and microstructural analyses are also performed through an impedance analyzer and a scanning electron microscope, respectively. The effects of solid loading for two anode and two cathode contact paste materials which provide the best two performances during the electrochemical performance tests are also studied. After optimizing the solid loading in the anode and cathode contact paste according to the performance results, the best contact materials for each side are decided. The final short stack is then installed by using the best combination of contact pastes and then tested. The final cell shows 0.39Wcm−2 and 0.90Wcm−2 peak power densities at 700°C and 800°C, respectively, whereas the base cell provides only 0.26Wcm−2 peak power density at 800°C. The improvement in the cell performance is considered to be due to the enhanced contact and better current collecting by employing contact pastes. [ABSTRACT FROM AUTHOR]

Abstract: Pellets of LiFePO4, synthesised by solid state reaction, were sintered at two temperatures, 650 and 770°C and their electrical properties measured by impedance spectroscopy over the temperature range 75 to 300°C. Various equivalent circuits were tested to model the impedance data and a good fit to the bulk response obtained for a parallel combination of a resistance, R 1, capacitance, C 1, and constant phase element, CPE1. For pellets sintered at 650°C, a second element, R 2–C 2–CPE2, was required, in series, to model an impedance attributed to a constriction resistance associated with the poorly sintered ceramic. At higher temperatures and low frequencies, evidence was obtained for a third impedance component attributed to a depletion layer associated with a Schottky barrier at the sample–electrode interface. [Copyright &y& Elsevier]

Abstract: Ceramic compositions based on (aY2O3 + bCeO2)–0.4YCr0.5Mn0.5O3 (a + b =0.6) were prepared by conventional solid state reaction at 1200°C, and sintered under air atmosphere at 1600°C. For 0≤ a <0.6, XRD patterns have shown that the major phases presented in the calcined powders are Y2O3, CeO2 and orthorhombic perovskite YCr0.5Mn0.5O3 phase, respectively. SEM and EDAX observations confirm the YCr0.5Mn0.5O3 phases mostly exist at the grain, whereas the Y2O3 and CeO2 phases mainly exist at the grain boundaries. Complex impedance analysis shows that, for 0< a ≤0.6, single semicircular arc whose shape does not show any change with temperature. Nevertheless, for a =0, two overlapping semicircular arcs are observed at and above 300°C. The grain boundary properties exhibit thermistor parameters with a negative temperature coefficient characteristic. The relaxation behavior and conduction for the grain boundary could be due to a space-charge relaxation mechanism and oxygen vacancies, respectively. [Copyright &y& Elsevier]

Impedance measurements were made on technological important ferroelectric ceramics, namely PZT and La0.75 Bi3.25Ti3O12 (BLT), in the frequency range of 100 Hz to 1 MHz, from room temperature to 500°C. Combined impedance and modulus spectroscopic analysis along with the detailed conductivity (ac and dc) data was used to understand the heterogeneity of the ceramics and the results were corroborated with temperature coefficient of dc-conductivity (figure of merit) data for the further understanding. AC-conductivity plots against frequency at different temperatures for PZT and BLT suggest the response of obeying Jonscher's and modified Jonscher's law, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The polycrystalline nanoceramics (∼60nm) of Ca(Fe2/3W1/3)O3 (CFW) were synthesized by mechanochemical and solid-state reaction techniques. Preliminary X-ray structural analysis of CFW suggested the formation of single-phase compound in tetragonal crystal system (distorted structure of ideal perovskite). The large distortion (∼16%) is supported by a large deviation of tolerance factor t=0.86 from unity (for ideal perovskite). The SEM micrograph shows the polycrystalline nature of the sample with different grain sizes, which are inhomogeneously distributed through the sample surface. Detailed studies of dielectric and impedance properties of the material in a wide range of frequency (1kHz–1MHz) and temperatures (300–630K) show that these properties are strongly temperature and frequency dependent. The nature of variation of AC conductivity exhibits a progressive increase in AC conductivity on increasing temperature. The oxygen vacancies, space charge and mobile charge carriers play an important role in relaxation and conduction process. The relaxation process in the material was found to be of non-Debye type. [Copyright &y& Elsevier]

A new polycrystalline layered ceramic oxide, LiFeVO4, has been prepared by a standard solid state reaction technique. The preparation conditions were optimised using thermogravimmetric analysis (TGA) technique. Material formation under the reported conditions was confirmed by X-ray diffraction studies. A preliminary structural analysis indicated that the crystal structure was orthorhombic with lattice parameters: a=4·3368 Å, b=13·1119 Å and c=16·3426 Å. The phase morphology and surface property were studied by scanning electron microscopy. Complex impedance analysis of the sample indicated bulk contribution to electrical properties at T≤125°C, grain boundary effects at the temperatures ≥125°C, negative temperature coefficient of resistance (NTCR) effect and evidence of temperature dependent electrical relaxation phenomena in the sample. The dc conductivity σdc shows typical Arrhenius behaviour when observed as a function of temperature. The activation energy value was estimated to be 0·24 eV. The value of σdc, evaluated from complex impedance spectrum, shows a jump of nearly two orders of magnitude at higher temperature (∼1·24 × 10-5 S cm-1 at 350°C) when compared with that of σdc (1·14 × 10-6 S cm-1 at 50°C). Alternating current conductivity spectrum obeys Jonscher's universal power law. The results of σac v. temperature are also discussed. [ABSTRACT FROM AUTHOR]

A new polycrystalline layered ceramic oxide, LiFeVO4, has been prepared by a standard solid state reaction technique. The preparation conditions were optimised using thermogravimmetric analysis (TGA) technique. Material formation under the reported conditions was confirmed by X-ray diffraction studies. A preliminary structural analysis indicated that the crystal structure was orthorhombic with lattice parameters: a=4·3368 Å, b=13·1119 Å and c=16·3426 Å. The phase morphology and surface property were studied by scanning electron microscopy. Complex impedance analysis of the sample indicated bulk contribution to electrical properties at T≤125°C, grain boundary effects at the temperatures ≥125°C, negative temperature coefficient of resistance (NTCR) effect and evidence of temperature dependent electrical relaxation phenomena in the sample. The dc conductivity σdc shows typical Arrhenius behaviour when observed as a function of temperature. The activation energy value was estimated to be 0·24 eV. The value of σdc, evaluated from complex impedance spectrum, shows a jump of nearly two orders of magnitude at higher temperature (∼1·24 × 10-5 S cm-1 at 350°C) when compared with that of σdc (1·14 × 10-6 S cm-1 at 50°C). Alternating current conductivity spectrum obeys Jonscher's universal power law. The results of σac v. temperature are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Complex impedance analysis of a new rare earth-based ceramic oxide, LaLiMo2O8, prepared by a standard solid-state reaction technique has been carried out. Material formation under the reported conditions has been confirmed by X- ray diffraction studies. A preliminary structural analysis indicates the crystal structure to be orthorhombic. Electrical properties of the material sample have been studied using AC impedance spectroscopy technique. Impedance spectrum results indicate that the electrical properties of the material are strongly dependent on temperature and it bears a good correlation with the sample microstructure (i.e. the presence of bulk, grain boundary, etc.) in different temperature ranges. Evidences of temperature-dependent electrical relaxation phenomena in the material have also been observed. The bulk resistance, evaluated from complex impedance spectrum has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR)-type behavior like that of semiconductors. The DC conductivity shows typical Arrhenius behavior when observed as a function of temperature. The AC conductivity spectrum has provided typical signature of an ionically conducting system and is found to obey Jonscher''s universal power law. Modulus analysis has indicated the possibility of hopping mechanism for electrical transport processes in the system with non-exponential-type conductivity relaxation. [Copyright &y& Elsevier]