Synthesis, electrical and thermal properties of Bi4V2−xMexO11 (x = 0.0 and 0.02) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me = Nb, Zr, Y and Cu and x = 0.0 and 0.02) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 380 °C and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the heat capacity and heat flow of the compounds. The results are discussed in detail.     

Synthesis,electrical and thermal properties of Bi4V2−xMexO11 (Me=Nb,Zr, Y and Cu with x = 0.0 and 0.06) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me=Nb, Zr, Y and Cu and x = 0.0 and 0.06) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy, and hence, its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 723 K and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the phase transition (heat capacity and heat flow) of the compounds. The results are discussed in detail.     

Synthesis, structural, electrical and thermal properties of Ti-doped Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2?xTi_xO₇ (x?=?0.0, 0.2, 0.4, 0.6, 0.8) have been synthesized by conventional solid-state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural, morphological, electrical and thermal properties of the pure Bi₂Sn₂O₇ ceramics have been studied by X-ray diffraction (XRD) followed by scanning electron microscopic techniques, dc conductivity and modulated differential scanning calorimetry. The XRD analysis carried out by performing the Rietveld refinement using the space group Fd3m indicates that the increase of titanium contents do not lead to any secondary phase. The grain size distributions of all the samples were investigated by SEM. It was found that the grain sizes are strongly influenced by the addition of titanium to the system. The frequency and temperature dependent dielectric studies have been carried out. The dc conductivity measurement was carried out for all the compounds and the activation energies were calculated using the relation ???=???0 exp(?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the specific heat, heat flow and other thermal parameters of the compounds. The results are discussed in detail.     

Single Phase Formation,Cation Distribution,and Magnetic Characterization of Coprecipitated Nickel-Zinc Ferrites

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni_1-xZn_xFe₂O₄ nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and possible nonmagnetic impurities. The influence of zinc substitution on the magnetic exchange interactions were studied based on molecular-field theory for compositions of 0 ≤x ≤ 0.4.     

Synthesis, growth, thermal, optical, mechanical and dielectric studies of N-succinopyridine

Organic nonlinear optical (NLO) material, N-succinopyridine (NSP), was synthesised and bulk single crystals were grown from aqueous solution using isothermal solvent evaporation technique. The stoichiometric form of NSP has been confirmed by carbon–hydrogen–nitrogen analysis. NSP crystallizes in orthorhombic system with non-centrosymmetric space group P2₁2₁2₁ and unit cell dimensions a = 7.721(2) Å, b = 7.762(3) Å, c = 14.951(3) Å. The thermal stability, thermal decomposition and specific heat capacity of NSP have been investigated by thermogravimetric/differential thermal analysis, differential scanning calorimetric (DSC) analysis and modulated DSC analysis. A wide transparency window, 294–1,100 nm, useful for optoelectronic applications is indicated by UV–Vis–NIR studies. The NLO second harmonic generation efficiency analysis using Nd:YAG laser (1,064 nm) revealed that the SHG efficiency of NSP is about 1.2 times higher than that of standard potassium dihydrogen phosphate powder of comparable size and more importantly that it is phase-matchable. The room temperature mechanical behaviours of NSP have been tested using Vicker’s microhardness tester and the results were analysed through classical Mayer’s law. The dielectric behaviours such as dielectric constant, dielectric loss and ac conductivity of NSP single crystal have also been investigated as a function of frequency (20 Hz–1 MHz) and temperature (308–358 K).     

Microstructure and dielectric properties of Nd doped CaCu3Ti4O12 synthesized by sol–gel method

Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2 and 0.3) powders and ceramics were prepared by sol–gel method. Effect of Nd on microstructure and dielectric properties were investigated. XRD patterns suggest that pure perovskite-like CCTO phase were obtained after calcining at 800 °C for 2 h. SEM pictures reveal that particle size monotonously decreases from 250 to 120 nm with increase of Nd concentration. The lattice parameters show an increasing trend with the enhancing amount of Nd³⁺ substitution. The average grain size of CCTO ceramics decrease from 2.0 to 0.8 μm with increase in Nd doping, which indicates that high concentration of Nd inhibits grain growth of CaCu₃Ti₄O₁₂. Both of the dielectric constant and dielectric loss decrease with increase in Nd concentrations. Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ ceramics with x = 0.3 shows the lowest dielectric constant of 1.12 × 10⁴ as well as the lowest dielectric loss value of 0.12 at 20 °C(10 kHz).     

Study on the solid solution of YMn1−xFexO3: Structural, magnetic and dielectric properties

The solid solution of YMn_1−xFe_xO₃ (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO₃ was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O₃ phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d⁵ ion (high spin Fe³⁺ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed.     

Preparation of Bi0.4Sb1.6Se3xTe3(1−x) hexagonal rods and effect of Se on structure and electrical property

In the current study, novel hexagonal rods based on Bi_0.4Sb_1.6Te₃ raw materials and dispersed with x amounts of Se (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in the form Bi_0.4Sb_1.6Se_3xTe_3(1−x) were synthesized via a standard solid-state microwave route. The morphologies of these rods were explored using field emission scanning electron microscopy (FESEM). The crystalline of the powders were examined by X-ray diffraction (XRD), which showed that the powders of 0.0 ≤ x ≤ 0.8 samples can be indexed as the rhombohedral phase, whereas the sample with x = 1.0 has an orthorhombic phase structure. The influence of variations in Se content on thermoelectric properties was studied in the temperature range of 300–523 K. The alloying of Se in Bi_0.4Sb_1.6Te₃ effectively caused a decrease in hole concentration and, thus, a decrease in electrical conductivity and an increase in Seebeck coefficient. The maximal power factor measured in the present work was 7.47 mW/m K² at 373 K for the x = 0.8 sample.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Electron doping effect on structural and magnetic phase transitions in Sr2−xNdxFeMoO6 double perovskites

Polycrystalline Sr_2−xNd_xFeMoO₆ (x=0.0, 0.1, 0.2, 0.4) materials have been synthesized by a citrate co-precipitation method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature-dependent NPD data shows that the compounds (x=0.0, 0.1, 0.2) crystallize in the tetragonal symmetry in the range 10-400 K and converts to cubic symmetry above 450 K. The unit cell volume increases with increasing Nd³⁺ concentration, which is an electronic effect in order to change the valence state of the B-site cations. Antisite defects at the Fe-Mo sublattice increases with the Nd³⁺ doping. The Curie temperature was increased from 430 K for x=0 to 443 K for x=0.4. The magnetic moment of the Fe-site decreases while the Mo-site moment increases with electron doping. The antiferromagnetic arrangement causes the system to show a net ferrimagnetic moment.     

Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

Effect of Mn-substitution on structural and dielectric properties of Pb(Zr0.65−xMnxTi0.35)O3 ceramics

The polycrystalline samples of Pb(Zr_0.65?xMn_xTi_0.35)O₃ (x = 0, 0.05, 0.10, 0.15) (PZMT) were prepared by a high-temperature solid-state reaction technique. Structural properties of the compounds were examined using an X-ray diffraction (XRD) technique to confirm the formation of single-phase compounds (with perovskite structure) at room temperature. Microstructural analysis of the surface of the compounds by scanning electron microscopy (SEM) exhibits that there is a significant change in grain size on introduction, at the Zr-site, of Mn. Detailed studies of the dielectric properties of PZMT show a measurable shift in T_c, change in dielectric constant, and ac conductivity.     

GPS patch antenna performance by modification of Zn(1−x)CaxAl2O4-based microwave dielectric ceramics

This study reports the characterization, fabrication, and performance of global positioning systems (GPS) patch antennas as a function of calcium (Ca) concentration and dielectric constant (? _r ). Zn_(1?x)Ca_xAl₂O₄ (x = 0.00, 0.05, 0.10, 0.20, 0.25, and 0.30) thin films were prepared through a sol–gel method. The effects of added Ca on the nanostructures and dielectric properties of ZnAl₂O₄ ceramics were investigated. The addition of Ca increased the crystallite size, grain size, and surface morphology, thereby increasing the density and dielectric constant. As the Ca content increased, the ? _r values linearly increased. However, the Q _u values decreased (at x = 0.25 to x = 0.25) after achieving the optimum values at x = 0.20. Finally, GPS patch antennas were successfully fabricated using the Zn_(1?x)Ca_xAl₂O₄ material. The patch antenna sizes decreased as ? _r increased from 2.88  × 4.37 cm (? _r  ≈ 8.52) to 2.88  × 4.37 cm (? _r  ≈ 10.16). The performance (return loss analysis) and operating frequencies of the GPS patch antennas were measured using the PNA series network analyzer. Results show that the patch antenna resonates at frequency of 1.570 GHz and produces a return loss bandwidth between ?16.6 and ?27.5 dB. The optimal performance of GPS patch antenna with ? _r  ≈ 9.95, Q _u  ≈ 6,186, and return loss = ?27.5 dB was obtained from specimen using Zn_0.80Ca_0.20Al₂O₄ (x = 0.20) ceramics.     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.     

Conductance of HCl,NaCl, Na acetate,and acetic acid in water-ethylene carbonate solvent mixtures at 25 and 40°C

The molar conductances of solutions of hydrochloric acid, sodium chloride, sodium acetate, and acetic acid were measured in water-ethylene carbonate (EC) solvent mixtures at 25 and 40°C. These solvents have dielectric constants higher than that of water. Four solvent compositions, in which the mole fraction (x ₂) of EC was 0.2, 0.4, 0.5, and 0.6, were studied at 25°C. For HCl and acetic acid at 40°C, additional measurements were made atx ₂=0.8 and 1.0. Analysis of the data by the Pitts equation was successful up tox ₂=0.6 and for HCl tox ₂=0.8. A graphical method, together with ₀ derived from the measurements for HCl, NaCl, and NaAc, yielded the dissociation constant of acetic acid up tox ₂=0.6. As EC is added, all the compounds studied displayed increased ion association. The acidic strength of acetic acid is greatly reduced; the dissociation constant atx ₂=0.6 is only 1/1000 that in water. The behavior of these electrolytes reflects the poor solvating power of EC, and the dielectric constant plays only a minor role.     

Structural relaxation of PbO–WO3–P2O5 glasses

The structural relaxation of three compositional series of PbO–WO₃–P₂O₅ glasses with composition (0.5 ? x/2)PbO·xWO₃·(0.5 ? x/2)P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5; 0.5PbO·xWO₃·(0.5 ? x)P₂O₅, x = 0, 0.1, 0.2, and 0.3; and (0.5 ? x)PbO·xWO₃·0.5P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 was studied by thermomechanical analysis. The structural relaxation was studied in the transformation region using the Tool–Narayanaswamy–Moynihan’s and Tool–Narayanaswamy–Mazurin’s models. The relaxation function of Kohlrausch Williams and Watts was used. The parameters of both models were calculated by nonlinear regression analysis of thermodilatometric curves measured by thermomechanical analyzer under the constant load. Both models very well describe the experimental data. It was found that the modulus is increasing with increasing amount of WO₃ in all glasses. On the contrary, the width of the spectrum of relaxation times is decreasing with increasing amount of WO₃ in all studied glasses. Both models possess the values of metastable melt thermal expansion coefficient equal to their experimental value.     

Glass-ceramic nanocomposites in the [(1 − x)PbO–xBaO]–Na2O–Nb2O5–SiO2 system: Crystallization and dielectric performance

The crystallization process, microstructure and dielectric properties of [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ (PBNNS) (0 ≤ x ≤ 1) glass-ceramics prepared by controlled crystallization were investigated. The crystallization strategies for acquiring nano-crystallized PBNNS glass-ceramics were monitored by differential thermal analysis (DTA). X-ray diffraction (XRD) analysis revealed a major crystal phase transition in PBNNS glass matrix as the crystallization temperature increased. At low temperatures (700–750 °C), the major crystal phases precipitating in the glass matrix are identified as Pb₂Nb₂O₇ for x = 0, Ba₂NaNb₅O₁₅ for x = 1 and their solid solution for 0.2 ≤ x ≤ 0.8; while at higher temperatures (≥850 °C), heat treatment produces different crystalline phases, PbNb₂O₆ and NaNbO₃ for x = 0, Ba₂NaNb₅O₁₅ and NaNbO₃ for x = 1, and the solid solution of these three phases for 0.2 ≤ x ≤ 0.8. Corresponding to the result of phase transition, microstructural observation proves increasing crystallite sizes with increasing temperature of heat treatment. At different crystallization temperatures, the dielectric properties of the [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ glass-ceramics show a strong dependence on the chemical composition x. At low temperatures (700–750 °C), a maximum of the dielectric constant of the PBNNS glass-ceramic is found for the composition x = 0.6; while at higher crystallization temperatures (≥850 °C), the dielectric constants of all samples (0 ≤ x ≤ 1) exhibit decreasing values with increasing x.     

Effect of Tb content on microstructure and ferroelectric properties of Bi4−x Tb x Ti3O12 thin films grown by sol–gel method

The effects of Tb substitution on the structural and electrical properties of ferroelectric Bi₄Ti₃O₁₂ (BTO) thin films grown on Pt/TiO₂/SiO₂/Si substrates by a sol–gel process have been reported. X-ray diffraction indicated A-site Tb substitutions did not change the polycrystalline bi-layered Aurivillius structure of the BTO, but a lattice distortion was observed. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?2 to 10^?4 A/cm² with the increase of x under 150 kV/cm. The remnant polarization (2P _r ) and dielectric constant (ε _r) increase firstly and then decreases with the increase of the Tb content. We observed a substantial increase in the remnant polarization (2P _r ) with Tb substitution and obtained a maximum value of~60 μC/cm² at an applied electric field of 500 kV/cm for x = 0.4. Moreover, this BTT-0.4 capacitor did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles, suggesting an anti-fatigue character.     

Conduction mechanism in Y3−2xCa2xFe5−xVxO12 garnet ferrites

A series of polycrystalline garnet ferrites with composition Y_3−2xCa_2xFe_5−xV_xO₁₂ (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), were prepared by the standard ceramic technique to study the effect of Ca²⁺ and V⁵⁺ ions substitution on their DC electrical conductivity, thermoelectric power, charge carrier concentration and charge carrier mobility at different temperatures. It was found that the DC electrical conductivity increases linearly with increasing temperature ensuring the semiconducting nature of samples. The lines representing the temperature dependence of σ_dc are broken at two-phase transition temperature (T_σ1, T_σ2=T_C) giving three distinct regions (I, II and III). The activation energy for electrical conduction increases going from ferrimagnetic state (regions I and II) to paramagnetic state (region III) through the transition temperature T_σ2 (Curie temperature). It also increases going from region I to region II thorough the temperature T_σ1. The dc electrical conductivity does not vary uniformly with Ca²⁺ and V⁵⁺ ion substitution. The values of the thermoelectric power were positive for samples of 0.0⩽x⩽0.6 indicating that the majority of the carrier are holes in these samples while it were negative for samples of x⩾0.8 indicating that the majority of charge carriers are electrons in this samples. Using the values of the DC electrical conductivity and thermoelectric power, the values of the charge carrier concentration and the charge carrier mobility were calculated.     

Thermal conductivity of the ferrites Ni0.65Zn0.35CuxFe2−xO4

A series of samples of the type Ni_0.65Zn_0.35Cu_xFe_2?xO₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by a ceramic technique. The existence of a single phase was confirmed by X-ray studies. The thermal conductivity and specific heat were measured at 53°C. The thermal conductivity had a minimum value atx=0.3, due to the maximum porosity at this composition. The phonon frequency was estimated to have an optimum value at x=0.3, due to the increase in phonon scattering.