Specific features in the synthesis, crystal structure and electrical conductivity of BICUTIVOX

The formation of solid solutions Bi₄V_2 − xCu_x/2Ti_x/2O_11 − x (0.025 ≤ x ≤ 0.5) known as BICUTIVOX, synthesized by three different methods (a conventional solid-state synthesis, solid-state synthesis enhanced by mechanical activation, and through liquid precursors), has been studied. Based on crystal structure investigations carried out at different temperatures, ranges of stability and temperatures of phase transitions for different polymorphous modifications have been defined. The morphology and the local chemical composition of the ceramic samples obtained have been studied. Thermal expansion coefficients have been measured. The electrical conductivity of ceramic samples has been investigated in a wide range of temperatures and partial oxygen pressures.     

Synthesis, electrical and electromechanical properties of a tungsten-bronze ceramic oxide: Pb0.68K0.64Nb2O6

A tungsten-bronze ceramic oxide, Pb_0.68K_0.64Nb₂O₆, has been prepared by a standard solid-state reaction technique. Compound formation and phase identification has been confirmed by X-ray diffraction (XRD) studies. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 45 Hz–5 MHz and a temperature range 35–590 °C. Electrical properties of the material were studied using an impedance spectroscopic technique. Detailed analysis of the impedance spectrum suggested that the electrical properties of the material are strongly temperature dependent. The Nyquist plots clearly showed the presence of bulk and grain boundary effect in the compound. The imaginary part of modulus at different temperatures shows a relaxation peak and its position shifts to higher frequency with increase in temperature. This suggests a temperature-dependent relaxation. The frequency dependent ac conductivity at different temperatures indicated that the conduction process is thermally activated process.     

Synthesis, electrical and dielectric properties of FeVO4 nanoparticles

The electrical and dielectric properties of FeVO₄ nanoparticles were studied at different temperatures from ambient to 200 °C. The samples were prepared by simple co-precipitation method using ferric nitrate and ammonium metavanadate as the starting precursors. The powder X-ray diffraction pattern inferred the single phase formation and triclinic structure of FeVO₄. The morphology of the particles was elucidated from SEM studies. Detailed studies on the electrical and dielectric properties of the compound were carried out by using solid state impedance spectroscopy. A maximum dc conductivity of 4.65×10⁻⁵ S cm⁻¹ was observed at the measuring temperature of 200 °C. The calculated activation energy from dc conductivity was found to be 0.28 eV. It was evident that the electrical transport process in the system was due to the hopping mechanism. The detailed dielectric studies were also carried out.     

Correlation between phase structure and electrical conduction in BISNVOX system for intermediate temperature solid oxide fuel cells (IT-SOFC)

Samples of Sn⁴⁺-substituted bismuth vanadate, formulated as Bi₄Sn _x V_{2? x} O_{11?( x /2)? δ} in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ? β, β ? γ and γ′ ? γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ? β and β ? γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ? γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10^?5 S cm^?1 at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.     

Effect of La substitution on conductivity and dielectric properties of Bi1−xLaxFeO3 ceramics: An impedance spectroscopy analysis

Bismuth ferrite (BFO) and La-substituted BFO with composition Bi_1−xLa_xFeO₃ (x=0.05, 0.1 and 0.15) (BLFO_x=0.05-0.15) ceramics were prepared using the solid state reaction route. A structural phase transition from rhombohedral phase to triclinic phase was observed for BLFO_x=0.05-0.15 ceramics. Modulus spectroscopy reveals the deviation of dielectric behavior from ideal Debye characteristics and the dependence of conductivity on ion hopping in BFO and BLFO_x=0.05-0.15 ceramics. The conductivity of the BFO ceramics decreases for La content of 5 mol%, followed by a subsequent increase with 10 and 15 mol% of lanthanum doping. The typical values of the activation energies at high temperature reveal the contribution of short range movement of doubly ionized oxygen vacancies to the conduction process in BFO and BLFO_x=0.05 ceramics. Both short range and long range motion of oxygen vacancies are responsible for large conductivity in BLFO_{x=0.1 and 0.15} ceramics.     

Crystal structure,dielectric and piezoelectric properties of Ta/W codoped Bi3TiNbO9 Aurivillius phase ceramics

Aurivillius phase Bi₃Ti_1−xTa_xNb_1−xW_xO₁₂ high temperature piezoceramics were prepared by a conventional solid state reaction method. The crystal structure, dielectric, electrical conduction and piezoelectric properties were systematically studied. Pure or modified Bi₃TiNbO₉ ceramics revealed the presence of only two-layered Aurivillius phase, indicating that Ta/W doping entered into the B-site of pseudo-perovskite structure and formed solid solutions. The Curie temperature had a strong reliance on the structural distortion. Furthermore, Ta/W dopants act as a donor doping, decrease the number of oxygen vacancies and facilitate the domain wall motion. As a result, Ta/W modifications significantly increase the DC resistivity and piezoelectric properties. Bi₃Ti_0.98Ta_0.02Nb_0.98W_0.02O₁₂ ceramics possess the optimum d₃₃ value (∼12.5 pC/N) together with a high T_C point (∼893 °C). Moreover, the resonance–antiresonance spectra demonstrate that the Ta/W-BTN ceramics are indeed piezoelectric in nature at 600 °C. The d₃₃ value of BTTNW-2 ceramic remains ∼12.2 pC/N after annealing at 700 °C. These factors suggest that the BTTNW-based ceramic is a promising candidate for ultra-high temperature sensor applications.     

Preparation, characterization and oxide ion conductivity in U-substituted Bi4V2O11

A Bi₂V_{1 − x − y}U_xBi_yO_{5.5 + 0.5x − y} solid solution derived from Bi₄V₂O₁₁ has been prepared and characterized with x up to 0.125 for y = 0. Partial substitution of U⁶⁺ for V⁵⁺ in Bi₄V₂O₁₁ leads to the stabilization at room temperature of the high-oxide ion conducting γ-phase, in contrast with other M⁶⁺ dopants which stabilize the β-phase. The lower conductivity in U substituted system compared with BICUVOX.10 is attributed to its higher activation energy. Conductivity values and activation energies of the U substituted phases compare well with Bi₂UO₆.     

Epitaxial erbium silicide films on(100) silicon: growth, structure and electrical properties

Erbium silicide layers were grown epitaxially on (100) Si. Electron microscopy results showed that ErSi_2−x layers grow on (100) Si with hexagonal and tetragonal crystalline structures, depending on the method of deposition, the substrate temperature and their stoichiometry. Electrical resistivity measurements show that the two crystalline phases of ErSi_2−x are metallic and have slightly different electronic and magnetic properties.     

Assessment of the electronic conductivity of core-shell, Fe-doped LSGM ceramics by impedance spectroscopy

The structure, microstructure and low-temperature electrical properties of core-shell-type mixed conductors based on lanthanum gallate with Fe-doped grain boundaries are analyzed in depth. Electron probe microanalysis revealed that the iron concentration in the grain-boundary regions (shell) is below 1 at.% and their thickness is no more than 1.5 μm. The low-temperature (< 400 °C) electronic conductivity is enhanced by up to 2-3 orders of magnitude with respect to the corresponding undoped ceramics, as revealed by the analysis of impedance spectra combined with microstructural information. The electronic transport numbers lie in the range between 0.35 and 0.1 at 275 to 400 °C, decreasing at higher temperatures, where the influence of grain boundaries on the overall transport properties vanishes and the ionic conductivity increases.     

Influence of zirconium doping on structure,microstructure, dielectric and impedance properties of strontium bismuth niobate ceramics

Efforts have been made in this work to enhance the dielectric properties of SrBi₂Nb₂O₉ (SBN) by partial substitution of Zr⁴⁺ for Nb⁵⁺. Systematic investigations on structure, microstructure, dielectric and impedance properties of the SrBi₂(Nb_2−(4/5)xZr_x)O₉ [where, x = 0, 0.1 and 0.2] ceramic samples were carried out to understand the effect of substitution of Zr⁴⁺ for Nb⁵⁺ in SrBi₂Nb₂O₉. The X-ray diffraction (XRD) investigations indicated that the lattice volume of SrBi₂(Nb_{2− (4/5)x}Zr_x)O₉ with x = 0.1 and 0.2 decreases compared to SBN. The SEM investigations revealed an increase in the size of grains and the change on shape of grains to elongated plate shaped structure with the increase of x (x = 0.1 and 0.2) in SrBi₂(Nb_2−(4/5)xZr_x)O₉. Higher Curie temperature and enhanced peak dielectric constant at the Curie temperature were observed for both the SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1 and 0.2 ceramic samples compared to SBN. Among the investigated compositions the higher Curie temperature and enhanced peak dielectric constant at the Curie temperature was observed for SrBi₂(Nb_2−(4/5)xZr_x)O₉ with x = 0.1.     

Microstructure and electrical properties of YSZ–NiO composites

The microstructure and electrical properties of YSZ (ionic)–NiO (electronic) composites were investigated. The electrical properties of the composites were examined using impedance spectroscopy between 160 and 630°C. The effects of grains and grain boundaries on the electrical conductivity of the composites vary with composition and temperature. With increasing temperature, the contribution of grain boundary to the total resistivity decreases for YSZ-rich compositions (NiO≤30 mol%). For NiO-rich compositions (NiO>50 mol%), the contribution of grain boundary resistance is variable with temperature, showing maxima near 530°C. Above 630°C, the grain boundary resistance is small for all compositions. With varying composition, grain boundary resistance is greater when the number of YSZ/NiO contacts is greater than the number of YSZ/YSZ or NiO/NiO contacts below 500°C. The temperature- and composition-dependence of grain and grain boundary conductivity is explained by the microstructure and thus by the distribution of the two phases together with variations in activation energy according to the composition.     

LiCoO2: formation, structure, lithium and oxygen nonstoichiometry, electrochemical behaviour and transport properties

The formation, structure and transport properties of LiCoO₂ are described. LiCoO₂ exhibits two crystal structures, depending on both the preparation method and synthesis temperature. High temperature lithium cobalt oxide (HT-LiCoO₂) has a hexagonal layered structure, while the low temperature oxide (LT-LiCoO₂) has a cubic spinel-related structure. The dependence of the morphological characteristics (grain size, size distribution, crystallinity) of LiCoO₂ on synthesis method as well as their effect on the electrochemical properties are extensively reviewed. As the electrochemical properties and the electrical conductivity strongly depend on the structure of the oxide, primary attention is given to lithium cobalt oxide with defect structure and lithium and oxygen nonstoichiometry.     

Influence of calcium substitution on the phase transition and ionic conductivity in BICAVOX oxide ion conductor

Samples of Bi₄Ca _x V_{2? x} O_{11?(3 x /2)?δ} in the composition range 0.07 ≤ x ≤ 0.30 were prepared by conventional solid state reactions. The stability of different phases as a function of composition was analysed by X-ray powder diffraction, FT-IR spectra, differential thermal analysis and AC impedance spectroscopy. For the compositions x ≤ 0.10, monoclinic α-phase structure is retained at room temperature. For x = 0.13, orthorhombic β-phase is observed, whereas for x ≥ 0.17, high O^2?conducting tetragonal γ-phase is stabilised. However, the highest ionic conductivity σ_300°C = 3.27 × 10^?4 S cm^?1 was observed for x = 0.17. This higher value of conductivity of the substituted compound as compared to the parent compound can be attributed to the increased oxygen ion vacancies generated as a result of cation doping. AC impedance spectroscopy reveals the fact that this ionic conductivity is mainly due to the grain contribution.     

Electrical and mechanical properties of graphene oxide on flexible substrate

Graphene oxide (GO) was deposited via the electrophoretic deposition (EPD) method to lower the oxygen concentration of graphene sheets for large-scale production. In addition, the direct synthesis of large-scale GO films using transfer processes on a polydimethylsiloxane (PDMS) substrate was conducted. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties. The Young's modulus values of films with thicknesses of 100–200 nm were 324–529 GPa. Moreover, the GO films exhibited excellent conductivity, with a sheet resistance of 276–2024 Ω/sq at 23–77% transparency. Experiments show that transfer processes for flexible substrates can produce high-quality cost-effective transparent conductive films.     

New quasi-one-dimensional tetracyanidoplatinate,Cs4[Pt(CN)4](CF3SO3)2: Synthesis,structure, and physical characterization

The synthesis and some physical properties of a new quasi-one-dimensional tetracyanidoplatinate, Cs₄[Pt(CN)₄](CF₃SO₃)₂ (CsCP(OTf)) are reported and described in comparison to the well-known K₂[Pt(CN)₄]Br_0.30·3.2H₂O (KCP). Single-crystal X-ray diffraction reveals Pt–Pt spacings to be greater than those of KCP by 5% longitudinal and 38% transverse, but much shorter than comparable spacings in other non-partially oxidized platinates. Anomalies are observed between temperatures 100 K and 200 K: (1) Longitudinal DC conductivity is two orders of magnitude higher and is non-monotonic with temperature, showing a minimum at around 170 K. (2) Nuclear magnetic resonance (NMR) longitudinal relaxation time T₁ is at least three orders of magnitude higher than that of KCP, and is also non-monotonic with temperature, showing a sharp peak at around 120 K. Since X-ray diffraction reveals no structural transition at 120 K, these suggest a possible lattice freezing or stiffening at around 120 K.     

Structural, ferroelectric and impedance spectroscopy properties of Y modified Pb(Fe0.5Nb0.5)O3 ceramics

Some ceramic samples of Pb_1−xY_x(Fe_0.5Nb_0.5)_1−x/4O₃ (PYFN) (0.00≤x≤0.08) were synthesized by a mixed oxide route. X-ray diffraction patterns of all the above samples confirm the formation of single phase material crystallizing in monoclinic structure. Dielectric properties (ε_r and tan δ) were analyzed in a wide temperature (30-350 °C) and frequency range (100 Hz-1 MHz). Ferroelectric properties of these compounds were confirmed from polarization (P-E hysteresis loop) measurements at room temperature. All the room temperature hysteresis loops of PYFN ceramics were well simulated using the ferroelectric capacitor model. Yttrium substitution resulted in notable enlargement of room temperature remnant polarization (2P_r). The 2P_r of PYFN (x=0.02) reaches to a large value (23 μC/cm²), which is nearly 5 times greater than that of PFN ceramic (4.6 μC/cm²). All the compounds exhibits negative temperature coefficient of resistivity (NTCR) type behavior as that of semiconductors. Dc conductivity (estimated via bulk resistivity) variation with temperature of all the samples follows Arrhenius type of electrical conductivity.     

Synthesis modified structural and dielectric properties of semiconducting zinc ferrospinels

The influence of preparation techniques on structural and dielectric properties of ZnCr_xFe_1−xO₄ (x=0, 0.1 abbreviated as Z and ZC) ferrite nano-particles synthesized using chemical co-precipitation (CCP), sol-gel (SG) and solid state reaction (SS) techniques is discussed. XRD profiles are used to confirm the single phase spinel ferrite formation. TEM images indicate the change in size and shape of particles on changing either the composition or the synthesis methodology. The TEM micrograph of samples obtained through CCP shows uniform particle size formation compared to those obtained through SG and SS. Sample prepared through CCP possess porosity >70% making these materials suitable for sensing applications. The dielectric loss, dielectric constant and ac conductivity are analyzed as a function of frequency, temperature and composition using impedance spectroscopy. A universal dielectric behavior has been predicted through temperature and frequency variations of different parameters. Dielectric constant is found to possess highest value for sample synthesized through SG which marks the possibility of using the SG derived ferrospinels as microwave device components.     

Electrical transport properties of consolidated ZnSe quantum dots at and above room temperature

Here we report a comprehensive study on the prevailing conduction mechanism and dielectric relaxation behavior of consolidated Zinc Selenide quantum dots in the frequency range of 1 kHz ≤ f ≤ 1.5 MHz and in the temperature range of 298K ≤ T ≤ 573 K. The ac conductivity increases either with increase in temperature or with increase in frequency, which is explained by the Jonscher Power law. At higher temperatures, correlated barrier hopping is found to be the prevalent charge transport mechanism with a maximum barrier height of 0.88 eV. The dielectric constant of the sample is found to exhibit weak temperature dependence. DC conductivity study reveals the semiconducting nature of the sample and it is discussed in the light of polaron hopping conduction. From the impedance spectroscopic study, role of the grains and grain boundaries in the overall electrical transport properties have been elucidated by considering an electrical equivalent circuit (composed of resistances and constant phase elements). Electric modulus study reveals non-Debye responses of the sample in the experimental range.     

Evolution of microstructure and dielectric properties of (LiCe)-doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

Aurivillius type (NaBi)_0.5?x(LiCe)_xBi₂Nb₂O₉ ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce⁴⁺ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb⁵⁺ ions by the Ce⁴⁺ ions.