Grain Boundary Capacitance Research Articles

Development of 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea derivatives as robust corrosion inhibitors for mild steel in 1 M HCl environment: Insight from ,molecular, experimental, and microscopic-scale modelling approaches

Cost-effective, novel urea derivatives, 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea (U-1), 1‐(4‐fluorophenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-2), and 1‐(4‐methylphenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-3) were synthesized to investigate as the corrosion inhibitors for mild steel/1 M HCl interface. Inhibition efficiency increases with the increasing inhibitor’s concentration but decreases with increasing temperature. Thermodynamic adsorption and activation parameters demonstrate that the adsorption of inhibitors follows Langmuir isotherm via physicochemical interactions. Potentiodynamic polarization measurements reveal that the inhibitors are mixed-type, impeding the charge-transfer process. Surface analysis supports a thin inhibitor film formation on the mild steel. The maximum inhibition efficiency of U-1, U-2 and U-3 are 94.97 ± 0.38%, 93.60 ± 0.62% and 97.42 ± 0.48% respectively. The calculated electrochemical impedance spectra (EIS) parameters such as ohmic resistance, double layer capacitance, relaxation time, effective thickness, and conductivity of grain and grain boundary are in-line with the efficiencies of NHUs. The performance of corrosion inhibitors follows a sequence U-3 > U-1 > U-2, emphasizing the influence of the substituent’s inductive effect (-CH3 > -H > -F) in inhibitors. Density functional theory (DFT) was performed to understand the correlation between molecular structure and inhibition efficiency. The Fukui indices confirm the presence of local attacking sites on the metal surface where inhibitors attack. A molecular dynamic (MD) simulation is used to determine the interaction energies between the inhibitors and mild steel. Radial Distribution Function (RDF) measurements confirm the existence of the chemical nature of the interaction. Furthermore, the diffusion coefficient of corrosive particles, self-diffusion coefficient of inhibitors, fractional free volume (FFV), and interaction between inhibitor’s film and corrosive particles are examined. Theoretical studies support experimental results.

Colossal dielectric response and complex impedance analysis of LaFeO3 ceramics

The present investigations mainly focused on the colossal dielectric response and complex impedance analysis of LaFeO3 ceramics. The studied sample was prepared by a citrate gel method. Structural and microstructural properties are analyzed from the XRD pattern and SEM micrograph. The anomalies in the dielectric constant versus temperature plots are analyzed on the basis of polarization induced by the Maxwell-Wagner mechanisms and ferromagnetic interaction between the Fe[Formula: see text] ions driven by the oxygen vacancy mediated Fe[Formula: see text]–V[Formula: see text] –Fe[Formula: see text] exchange interaction A giant dielectric permittivity in the order of [Formula: see text]105 was observed in the sample even at the room temperature for 100 Hz. The colossal dielectric constant in LaFeO3 is mainly driven by the internal barrier layer capacitor (IBLC) formation. The formation of IBLC was explained on the basis of highly insulating grain boundary and less resistive/semiconducting grain, which was confirmed from both the resistance and capacitance of grain and grain boundary from the impedance analysis. The non-Debye-type relaxation process associated with the grain and grain boundary effect was investigated from the broad and asymmetric relaxation peak. The relaxation time for both the grain and grain boundary effect was also calculated. In addition to this, we have also analyzed the normalized bode plot of imaginary part of impedance and electrical modulus which suggests the relaxation process dominated by the short-range movement of charge carriers.

Investigations on the Structural and Electrical Properties of Sm3+-Doped Nickel Ferrite–Based Ceramics

Compositions of ferrimagnetic NiSmxFe2−xO4 (0.00 ≤ x ≤ 0.25) ceramics were synthesized by the self-propagating sol-gel autocombustion method. Structural information was found using X-ray diffraction. It reveals that all the ceramics possess cubic symmetry of spinel ferrite with a small amount of orthoferrite phase SmFeO3, which is a ferroelectric material. The amount of phases and lattice parameter were determined by the Rietveld refinement method using the Fullprof suite software. As doping concentration increases, the secondary phase fraction of the ferroelectric SmFeO3 also increases. Due to the increase of the ferroelectric phase in NiFe2O4, the electrical properties of doped samples also modify. To know this modification, the electrical properties of these samples have been investigated. The room temperature dielectric and complex impedance analysis have been measured in the frequency range of 1–106 Hz. The dielectric behavior for x = 0.05 concentration (NiSm0.05Fe1.95O4) has a maximum dielectric constant value with a minimal loss tangent. Cole-Cole plot brings out the role of grain and grain boundaries in the bulk. Using impedance study, the resistance and capacitance of grain and grain boundaries have been determined. The ferroelectric behavior has been performed through the P-E (polarization versus electric field) and J-E (leakage current versus electric field) curves at room temperature.

Giant dielectric behavior of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics

AbstractGiant dielectric behavior and electrical properties of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics prepared by a solid‐state reaction route were systematically investigated. Substitution of Li+ and F− led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra‐high dielectric permittivity (ε′ ~7.7‐8.8 × 104) was achieved in the co‐doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu3Ti4O12 ceramics were increased by co‐doping with (Li+, F−). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell‐Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X‐ray photoelectron spectroscopy and found to originate from the presence of Cu+ and Ti3+ ions.

Colossal dielectric response and relaxation properties caused by Mg doping in Co2Y-Type hexaferrites

Mg doping effects on the dielectric response and relaxation behavior in Ba2Co2-xMgxFe12O22 are experimentally studied for doping range of 0≤x≤1 through measurements of dielectric constant, loss and impedance spectroscopy as functions of temperature and frequency. It is shown that a colossal dielectric response with dielectric constant higher than 103 near room temperature for a wide range of frequency up to ~1 MHz can be realized by Mg doping at Co sites. Our results demonstrate that Mg doping can cause three obvious effects, namely, (i) to decrease Co3+ ions and in turn increase Fe ions in octahedrons, (ii) to raise the activation energy of relaxation and (iii) to increase resistance and capacitance of grain boundary. Our results also demonstrate that the dielectric relaxation is gradually changed from the intragranular- to the intergranular-dominated relaxation with increasing Mg doping content, perhaps due to the doping-caused increase in both resistance and capacitance of grain boundary.

Impedance Spectroscopy Analysis of Orthorhombic DyMnO3 Ceramics

Orthorhombic DyMnO3 ceramics were synthesized by means of standard high-temperature solid-state reaction technique. Impedance spectroscopy analysis (complex impedance Z* and complex modulus M*) were performed by using the nondestructive complex impedance spectroscopy technique in the frequency range of 100–10 MHz at different temperatures. The impedance spectroscopic plots were used to discern the intrinsic DyMnO3 grain and grain boundary contributions to the dielectric responses. The radii of semicircles in Z″ vs. Z′ plot (Z′ and Z″ are real and imaginary parts of Z*) increased with decreasing temperature, which suggest the increased grain resistance. Similarly, the radii of semicircles in M″ vs. M′ plot (M′ and M″ are real and imaginary parts of M*) suggest that the grain capacitance increased as the temperature decreased. The resistance and capacitance of grain boundaries seem to be independent of the investigated temperatures. The dielectric response from electrodes with demarking frequency was extracted from the presentation of Z′ vs. Z″/f, where f is the frequency of the applied field.

Complex Electric Modulus Spectroscopy of (MnFe2O4)x/CuTl-1223 Nanoparticles-Superconductor Composites

Manganese ferrite (MnFe2O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10−δ(CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction methods, respectively. Different contents of MnFe2O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (MnFe2O4) x /CuTl-1223; x = 0∼2.0 wt% nanoparticles-superconductor composites. Complex electric modulus spectroscopy measurements of (MnFe2O4) x /CuTl-1223 composites were carried out at different test frequencies from 20 Hz to 10 MHz and at different operating temperatures from 78 to 253 K to analyze and interpret the dynamical aspects of electrical transport phenomena (i.e., such as carrier hopping rate, conductivity, and blocking factor). The complex electric modulus spectra showed the effects of both grains and grain-boundaries on electrical properties. The capacitance of grain-boundaries was found higher than that of grains. The capacitive behavior of grains was increased and that of grain-boundaries was decreased with increasing operating temperature for all these samples. Blocking factor of these composites was increased with increasing contents of MnFe2O4 nanoparticles. Shifting of peaks in imaginary part of modulus spectra towards lower frequency with increasing contents of these nanoparticles showed non-Debye type relaxation phenomenon in the material.

Dielectric response mechanism and suppressing high-frequency dielectric loss in Y2O3 grafted CaCu3Ti4O12 ceramics

Ca1−3x/2Y x Cu3Ti4O12 (0 ≤ x ≤ 0.67) ceramics were fabricated by a conventional solid-state reaction method. Lattice parameter of the system increases linearly with increasing x. The high-frequency dielectric loss of Ca1−3x/2Y x Cu3Ti4O12 is suppressed significantly while the dielectric constant decreases slightly. The dielectric, impedance and modulus spectra reveals that the giant dielectric response associates with the Maxwell–Wagner effect. The decrease of dielectric constant is just related to the capacitance of grain boundaries. The dielectric relaxation behavior of the system is independent of Y substitution while the correlation between conductivity and frequency becomes stronger in Y substituted CaCu3Ti4O12. It suggests that space charge and long-range hopping of carriers play important roles on the low-frequency dielectric properties. The decrease of grain-boundary activation energy with Y substitution indicates that the concentration of oxygen vacancies increases in grain boundaries. The mechanisms of depressing low-frequency dielectric constant and high-frequency dielectric loss was discussed.

Central role of TiO2 anatase grain boundaries on resistivity of CaCu3Ti4O12-based materials probed by Raman spectroscopy

This study focuses on characterization and control of grain boundaries to enhance the properties of CaCu3Ti4O12 (CCTO) ceramics capacitors for industrial applications. A novel factor deals with TiO2 anatase revealed by Raman scattering in grain boundaries, found as a dominant parameter of largest sample resistivity, consistent with higher grain boundary resistivity and higher breakdown voltage. Four selected samples of CCTO-based compositions showing very different properties in terms of permittivity ranging from 1000 to 684 000 measured at 1 kHz, capacitance of grain boundaries ranging from 8 10−10 to 4.5 10−7 F cm−1, grain boundary resistivity ranging from 193 to 30,000,000 Ω cm and sample resistivity extending from 450 to 1011 Ω cm. The relationship between permittivity weighted by grain size and capacitance of grain boundaries confirms the internal barrier layer capacitance model over 5 orders of magnitude.

Influence of precursor molar concentration on the electrical and magnetic properties of synthesized MnS nanocrystals

MnS Nanocrystals have been synthesized with 1:1, 1:2 and 2:1 molar ratio of precursors using wet chemical method. The electrical and magnetic properties of as-synthesized MnS nanocrystals have been investigated using the impedance spectroscopy and vibrating sample magnetometer respectively. An increase in dielectric constant from 68.5 to 87.9 with increasing Mn content and decrease to 54.1 with increase in the sulfur content was observed. Both the dielectric constant and the loss factor increased with temperature due to the Maxwell–Wagner type interfacial space-charge polarization. The Cole–Cole plot confirmed that the conduction in as-synthesized samples are through the grain and grain boundaries. The resistance and capacitance of grain and grain boundaries have been calculated. The grain resistance varies from 248 to 199 Ω whereas the grain boundary resistance varies from 16 to 6.7 KΩ over the temperature ranges of 323–473 K for 1:1 sample. It endorsed the NTCR type behavior in all the samples. The electric modulus representation revealed the well-defined relaxation peaks. The relaxation time versus temperature behavior revealed that the relaxation time decreases with increase in temperature. AC-conductivity (σac) increases with increasing frequency and temperature. σac increases from 1.58 × 10−5 to 1.51 × 10−3 S cm−1 with the increase of Mn content and then decreases to 1.22 × 10−8 S cm−1 with increase of sulfur content. The activation energy is found to be 0.35 eV (1:1), 0.64 eV (1:2) and 0.28 eV (2:1) at 3 kHz. The chemically modified MnS nanocrystals exhibit paramagnetic behavior. A typical saturation magnetization of 0.56, 0.38, and 0.57 emu/g and coercivity of 2.31, 8.42, and 5.57 Oe at room temperature for 1:1, 1:2 and 2:1 sample respectively.

Improving NASICON Sinterability through Crystallization under High-Frequency Electrical Fields

The effect of high frequency (HF) electric fields on the crystallization and sintering rates of a lithium aluminum germanium phosphate (LAGP) ion conducting ceramic was investigated. LAGP with the nominal composition Li1.5Al0.5Ge1.5(PO4)3 was crystallized and sintered, both conventionally and under effect of electrical field. Electrical field application, of 300V/cm at 1MHz, produced up to a 40% improvement in sintering rate of LAGP that was crystallized and sintered under the HF field. Heat sink effect of the electrodes appears to arrest thermal runaway and subsequent flash behavior. Sintered pellets were characterized using XRD, SEM, TEM and EIS to compare conventionally and field sintered processes. The as-sintered structure appears largely unaffected by the field as the sintering curves tend to converge beyond initial stages of sintering. Differences in densities and microstructure after 1 hour of sintering were minor with measured sintering strains of 31% vs. 26% with and without field, respectively . Ionic conductivity of the sintered pellets was evaluated and no deterioration due to the use of HF field was noted, though capacitance of grain boundaries due to secondary phases was significantly increased.

The origin of grain boundary capacitance in highly doped ceria.

The origin of a grain-boundary capacitance in mixed oxide-ion/electronic conductors has been investigated for the case of Ce0.8Sm0.2O1.9-δ using a.c. impedance spectroscopy under low pO2 from 250 to 400 °C. The observed capacitance is interpreted in terms of Ce(III):4f(1) electrons first introduced into the grains and not into the grain boundaries.

Contribution of grains and grain boundaries to dielectric relaxations and conduction of Aurivillius Bi4Ti2Fe0.5Nb0.5O12 ceramics

The dielectric response and electrical properties of Bi4Ti2Fe0.5Nb0.5O12 (BTFN) ceramics have been investigated by frequency and temperature dependent dielectric/impedance spectroscopy. The detailed frequency spectrum analysis demonstrates the existence of two dielectric relaxations in the ceramics. The high-frequency relaxation is evidenced to originate from the grains and the low-frequency relaxation is ascribed to the contribution of grain boundaries. The resistance of grain boundaries is much larger than that of grains, whereas the values of capacitance of grain boundaries and grains are in the same level. Above ~340°C, the conduction and relaxations of the material are attributed to the motion of ionized oxygen vacancies. As temperature above ~540°C is close to the ferroelectric transition temperature, the smart dielectric response to the external applied ac field was apparently reflected by the conductance of grain boundaries, the capacitance of grains and the consequent relaxations.

Synthesis, dielectric properties, and influences oxygen vacancies have on electrical properties of Na1/2Bi1/2Cu3Ti4O12 ceramics prepared by a urea combustion method

The influences of oxygen vacancies on the dielectric and electrical properties of Na1/2Bi1/2Cu3Ti4O12 ceramics prepared using a urea combustion method were investigated via an annealing treatment in an O2 atmosphere. Interestingly, a single Na1/2Bi1/2Cu3Ti4O12 phase was successfully prepared using a low calcination temperature of 800 °C. High dielectric permittivity (e′) and dense ceramic microstructure were achieved by sintering compacted powders at a low temperature of 980 °C. e′ and the loss tangent (tanδ) were decreased by annealing in an O2 atmosphere. This was associated with the oxygen vacancy concentration at grain boundaries (GBs). A decrease in low-frequency tanδ was caused by enhancement of GB resistance, which was due to filling oxygen vacancies at GBs. A slight decrease in e′ was attributed to the reduction in GB capacitance. Through use of an annealing process, the conduction activation energy at GBs was increased, whereas the conduction activation energy inside the grains remained unchanged. These results clearly indicated the effect of oxygen vacancy concentration at the GBs on the giant dielectric response and correlated GB response.

Dielectric relaxations and alternating current conductivity in manganese substituted cobalt ferrite

Manganese (Mn) substituted cobalt ferrites (CoFe2-xMnxO4, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.38 Å. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10−4 s and spreading factor of 0.35(±0.05). The frequency (20 Hz–1 MHz) and temperature (T = 300–900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1–10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz–1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO.

The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

Effect of tantalum substitutions on microstructures and dielectric properties of calcium copper titanate (CaCu3Ti4O12) ceramic

► CaCu 3 Ti 4− x Ta x O 12 ( x = 0.05, 0.10) ceramic was synthesized by novel semi-wet route. ► On increasing Ta 5+ content, dielectric constant increases at all temperatures. ► The modulus studies confirm the capacitance of grains and grain boundaries decreases with increasing temperature. Tantalum (Ta 5+ ) doped CaCu 3 Ti 4− x Ta x O 12 ( x = 0.05 and 0.10) ceramics were prepared by semi-wet route using solid Ta 2 O 5 powder and metal nitrate solutions. Powder X-ray diffraction confirmed the major phase formation of cubic CaCu 3 Ti 4 O 12 ceramic in the doped samples sintered at 900 °C for 6 h. Microstructure has been studied using field-emission scanning electron microscopy. The grain size is in the range of 150 nm to 1 μm for both compositions. Dielectric constant of the samples increases with increasing tantalum concentrations.

Evaluation of Microstructural Evolution of Nanostructured Yttria-stabilized Zirconia During Sintering Using Impedance Spectroscopy

A non-destructive evaluation (NDE) technique of impedance spectroscopy (IS) was employed for studying the sintering process of nanostructured yttria-stabilized zirconia (YSZ) after exposure at 1100 °C in air for different times. The variations within microstructure of YSZ were correlated with the EIS parameters. The results showed that the resistance and capacitance of YSZ grains (g) and grain boundaries (gb) varied with the sintering time. The resistance of YSZ g and gb increased significantly in 10 h, which may correspond to closure of pores. While during the stage from 10 to 200 h, the resistance of the g was basically consistent, and the gb decreased with the growth of g, which indicated that the gb resistance was more sensitive to grain size. The change of porosity and pore shape could be interpreted through impedance parameters. The porosity decreased and the shape of pores became smaller and rounder with the increasing sintering time.

Study of dielectric behavior and electrical properties of hematite α-Fe2O3 doped with Zn

The effects of Zn-doping on the dielectric behavior and electrical properties of bulk ?-Fe2O3 have been studied. X-ray diffraction analysis revealed the presence of two phases in all samples: hematite and spinel ZnFe2O4, with the amount of spinel phase increasing with increasing Zn content. Scanning electron microscopy analysis combined with energy dispersive X-ray spectroscopy showed that the Zn-bearing phase occurred in the form of individual spinel ZnFe2O4 grains in a hematite matrix. DC conductivity was measured in the temperature range 25-225oC (298-498 K). Impedance spectroscopy measurements in the same temperature range were carried out in the frequency range 100Hz to 10 MHz. Increase in the Zn content resulted in increased electrical conductivity and higher values of the dielectric constant. The resistance and capacitance of grains and grain boundaries were analyzed by modeling the experimental results using an equivalent circuit.

Fabrication and Characterization of Colossal Dielectric Response of Polycrystalline Ca1-x SrxCu3Ti4O12 (0≤x≤1) Ceramics

ABSTRACTWe report the microstructures and dielectric properties of Ca1-xSrxCu3Ti4O12 (C1-xSxCTO, 0≤x≤1) ceramics sintered at the various sintering temperatures ranging from 1000 to 1060˚C in air. The linear increase in lattice parameter in C1-xSxCTO (0≤x≤1) ceramics is observable for the full range of substitution. However, the second phases of SrTiO3 and CuO start to occur from the composition of x=0.8, implying that a stoichiometric SrCu3Ti4O12 (SCTO) compound may not exist. While the C0.6S0.4CTO and C0.4S0.6CTiO samples exhibit relatively lower dielectric constant (εr) of ∼40,000 below 1 kHz, the CaCu3Ti4O12 (CCTO) and SCTO show the extremely high εr values of ~120,000 and ∼180,000, respectively. Complex impedance (Z*) and modulus (M*) spectroscopy revealed that the capacitance (C) and resistivity (ρ) values of grain boundary in all samples are much higher than those of grains.