Minimum Hopping Length Research Articles

Electrical transport in lead-free Na0.5Bi0.5TiO3 ceramics

Lead-free Na0.5Bi0.5TiO3 (NBT) ceramics were prepared via a conventional oxide-mixed sintering route and their electrical transport properties were investigated. Direct current (DC, σDC) and alternating current (AC, σAC) electrical conductivity values, polarization current (first measurements) and depolarization current, current–voltage (I–U) characteristics (first measurements), and the Seebeck coefficient (α) were determined under various conditions. The mechanism of depolarization and the electrical conductivity phenomena observed for the investigated samples were found to be typical. For low voltages, the I–U characteristics were in good agreement with Ohm’s law; for higher voltages, the observed dependences were I–U2, I–U4, and then I–U6. The low-frequency σAC followed the formula σAC–ωs (ω is the angular frequency and s is the frequency exponent). The exponent s was equal to 0.18–0.77 and 0.73–0.99 in the low- and high-frequency regions, respectively, and decreased with temperature increasing. It was shown that conduction mechanisms involved the hopping of charge carriers at low temperatures, small polarons at intermediate temperatures, and oxygen vacancies at high temperatures. Based on AC conductivity data, the density of states at the Fermi-level, and the minimum hopping length were estimated. Electrical conduction was found to undergo p–n–p transitions with increasing temperature. These transitions occurred at depolarization temperature Td, 280 ℃, and temperature of the maximum of electric permittivity Tm is as typical of NBT materials.

Dielectric relaxation and study of electrical conduction mechanism in BaZr0.1Ti0.9O3ceramics by correlated barrier hopping model

AbstractThis work aims to study the electrical conduction mechanism in the dielectric material BaZr0.1Ti0.9O3(BZT) ceramics by applying AC signal in the frequency range of 102Hz to 106Hz. The phase purity and microstructure of the sample have been studied by X-ray diffraction refinement and field-emission scanning electron microscope (FE-SEM) analysis. The appearance of resonance peaks in the loss tangent at high temperature is due to inherent dielectric relaxation processes of this oxide. The temperature dependent Cole-Cole plot has been studied in details to determine both the grain and grain boundary contribution to the conductivity. Electrical modulus analysis reveals that the hopping of charge carriers is the most probable conduction mechanism in BZT ceramics. The obtained data of AC conductivity obey the universal double power law and have been discussed in terms of microstructural network characteristics. The behavior of frequency exponent n of AC conductivity as a function of temperature verify the applicability of the correlated barrier hopping (CBH) model. The AC conductivity data are used to estimate the minimum hopping length, density of states at Fermi level, thermal conductivity and apparent activation energy. The value of activation energy confirms that the oxygen vacancies play a vital role in the conduction mechanism.

Effect of Gadolinium doping on structural, ferroic and electrical properties of 0.8BiGdxFe1−xO3-0.2PbTiO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) composites

The Gadolinium (Gd) doped multiferroic composites of 0.8BiGdxFe1−xO3-0.2PbTiO3 with x = 0.00, 0.05, 0.10, 0.15 and 0.20 were prepared by the conventional solid state reaction technique. The phase formations of the composites were checked by using X-ray diffraction technique and distorted rhombohedral structure was confirmed for all the composites at room temperature. The ferroelectric and ferromagnetic properties were investigated by means of a computer based PE-Scanner and Vibrating- Sample Magnetometer (VSM) respectively. A significant change in the dielectric and magnetic properties were observed by the doping of rare earth (Gd). The dielectric and electrical properties of these composites were analysed by using an impedance analyser for a wide range of temperatures and frequencies (102–106 Hz). The impedance spectroscopy study confirms the presence of bulk effect only. The impedance plots obey non Debye type of relaxation for all the composites. The frequency dependent ac conductivity obeys Jonscher's universal power law. By applying the Correlated Barrier Hopping (CBH) model to ac conductivity data, the density of state at Fermi level and minimum hopping length has been estimated to understand the conduction mechanism within the composites.

Nd doped lead titanate crystals for microelectronic memory device applications

Using high energy ball milling technique the nanocrystalline Pb1−3x/2NdxTiO3 (where x = 0.01), abbreviated as PNT, ceramics with tetragonal shape has been synthesized and analyzed through X-ray diffraction and scanning electron microscope analysis. The frequency dependent ac conductivity and dielectric constant measurements of the PNT ceramics sintered at 800, 900, 1000 and 1100 °C has been performed in the 100–525 °C temperature range and the density of states at the Fermi level evaluated. The minimum hopping length and dielectric constants in PNT has been explained successfully using the correlated barrier hopping model. With first order correction to energy the quantum theory of ferroelectric has been applied to explain the dielectric behavior in the paraelectric phase. The explanation for density of states at morphotropic phase boundary and the conduction mechanism of charge transport were found to be in good agreement with the experimental observations.

Green synthesis and characterization of Ag1/2Al1/2TiO3 nanoceramics

Abstract Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Impedance and a.c. conductivity studies of Ba(Pr1/2Nb1/2)O3 ceramic

Impedance and electrical conduction studies of Ba(Pr1/2Nb1/2)O3 ceramic prepared through conventional ceramic fabrication technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group, \({Pm\overline 3 m}\). EDAX and SEM studies were carried out to study the quality and purity of compound. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using impedance data. Complex impedance as well as electric modulus analyses suggested dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Pr1/2Nb1/2)O3. The a.c. conductivity data were used to evaluate density of states at Fermi level, minimum hopping length and apparent activation energy.

Structural and electrical properties of lead free ceramic: Ba(Nd1/2Nb1/2)O3

Impedance and electrical conduction studies of Ba(Nd1/2Nb1/2)O3 ceramic prepared using conventional high temperature solid-state reaction technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group p Pm3m. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of compound. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealized model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Nd1/2Nb1/2)O3. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.

Studies on Electric and Dielectric Properties of Porous Sm0.5Sr0.5CoO3−δ

Frequency-dependent electric and dielectric properties of the porous Sm0.5Sr0.5CoO3−δ cathode prepared through conventional combustion synthesis technique were studied in the temperature range 298 K–973 K. The crystal symmetry, space group, and unit cell dimensions were confirmed by analyzing XRD pattern. XRD analysis indicates the formation of a single-phase orthorhombic structure with space group Pnma 62. Scanning electron microscopy technique was used to examine the morphology of the sample. Scanning electron microscopy study showed the formation of porous structure with an average grain size about 850 nm. From the electrical study, it is observed that the conduction in Sm0.5Sr0.5CoO3−δ sample takes place through the hopping mechanism and follows the inverse universal power law. The correlated barrier hopping model was employed successfully to explain the mechanism of charge transport in Sm0.5Sr0.5CoO3−δ. Further, the ac conductivity data was used to evaluate the minimum hopping length and apparent activation energy. The minimum hopping length was found to be ~10−4 times smaller than the grain size of Sm0.5Sr0.5CoO3−δ. The peaking behaviour of the real part of dielectric constant with frequency was explained using the Rezlescu model. This study helps to confirm that the charge transportation in Sm0.5Sr0.5CoO3−δ is due to two types of charge carriers.

Electrical Properties and AC Conductivity of (Bi0.5Na0.5)0.94Ba0.06TiO3 Ceramic

Lead-free perovskite (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT06) was prepared by conventional ceramic fabrication technique at 1160°C/3h in air atmosphere. The crystal structure, microstructure, dielectric, polarization, piezoelectric properties, and ac conductivity of the sample were studied. X-ray diffraction data confirmed the formation of a single phase tetragonal unit cell. Williamson-Hall plot was used to calculate the lattice strain and the apparent particle size. The experimental relative density of BNBT06 was found to be ~96-97% of the theoretical one with an average grain size ~4 μm. Room temperature dielectric constant and loss factor at 1 kHz were found to be equal to 781 and 0.085, respectively. Longitudinal piezoelectric charge coefficient of the poled sample under 2.5 kV/mm at 80°C in silicone bath was found to be equal to 124 pC/N. Complex impedance and electric modulus spectroscopic analyses showed the dielectric relaxation in the material to be of non-Debye type. The Nyquist plots and conductivity studies showed the NTCR character of BNBT06. The correlated barrier hopping model (CBHM) as well as jump relaxation model (JRM) was found to successfully explain the mechanism of charge transport in BNBT06. The ac conductivity data were used to evaluate the minimum hopping length, apparent activation energy, and density of states at Fermi level.

Structural and electrical properties of perovskite Ba(Sm1/2Nb1/2)O3-BaTiO3ceramic

The structural and electrical properties of <TEX>$(1-x)Ba(Sm_{1/2}Nb_{1/2})O_3-xBaTiO_3$</TEX>; (<TEX>$0{\leq}x{\leq}1$</TEX>) ceramics were prepared by conventional ceramic technique at <TEX>$1375^{\circ}C$</TEX>/7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were derived from the X-ray diffraction (XRD) data using FullProf software whereas crystallite size and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm m. Dielectric study revealed that the compound <TEX>$0.75Ba(Sm_{1/2}Nb_{1/2})O_3-0.25BaTiO_3$</TEX> is having low and <TEX>${\varepsilon}^{\prime}$</TEX> and <TEX>${\varepsilon}^{{\prime}{\prime}}$</TEX> a low <TEX>$T_{CC}$</TEX> (< 5%) in the working temperature range (up to+<TEX>$100^{\circ}C$</TEX>) which makes this composition suitable for capacitor application and may be designated as 'Stable Low-K' Class I material as per the specifications of the Electronic Industries Association. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in the system. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compounds.

Electrical Conduction in 0–3 BaTiO3/PVDF Composites

(1-x)PVDF-xBaTiO3 ceramic-polymer composites with x = 0.10, 0.20, 0.30 were prepared using melt growth technique. The crystal symmetry, space group and unit cell dimensions were determined from the XRD data of BaTiO3 using FullProf software, whereas crystallite size and lattice strain were estimated through Williamson-Hall approach. The distribution of BaTiO3 particles in the PVDF matrix were examined using a scanning electron microscope. The correlated barrier hopping model has been applied to the ac conductivity data in order to ascertain the conduction mechanism of charge transport in BaTiO3/PVDF composites. Also, the ac conductivity data have been used to estimate the apparent activation energy, density of states at Fermi level and minimum hopping length. Filler concentration dependent ac conductivity, density of states at Fermi level and minimum hopping length data followed definite trends of exponential growth/decay types of variation.

Structural and electrical properties of Ba(Sb1/2Nb1/2)O3 ceramic

Lead-free perovskite Ba(Sb1/2Nb1/2)O3 was prepared by conventional ceramic fabrication technique at 1200 °C/5 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from the experimental results using FullProf software whereas crystallite size and lattice strain were estimated from Williamson–Hall approach. XRD analysis of the compound indicated the formation of a single-phase monoclinic structure with the space group P2/m. EDAX and SEM studies were carried out to evaluate the quality and purity of the compound. Dielectric study revealed the frequency-dependent dielectric anomaly. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Sb1/2Nb1/2)O3. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compound.

Electrical properties of BaY 0.5Nb 0.5O 3 ceramic: Impedance spectroscopy analysis

Lead-free perovskite BaY 0.5Nb 0.5O 3 was prepared by conventional ceramic technique at 1375 °C/7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3̄m. EDAX, X-ray mapping and SEM studies were carried to study the quality and purity of the compound. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Electric modulus studies supported the hopping type of conduction in BaY 0.5Nb 0.5O 3. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in BaY 0.5Nb 0.5O 3. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compound.

Structural and electrical properties of lead free ceramic: Ba(La1/2Nb1/2)O3

Lead free perovskite Ba(La1/2Nb1/2)O3 was prepared by conventional ceramic fabrication technique at 1375°C for 7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single phase monoclinic structure with space group P2/m. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of the compound. Permittivity data showed low temperature coefficient of capacitance (TCC = 11%) up to 100°C. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealised model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(La1/2Nb1/2)O3. The AC conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.

Electrical conduction in (Na0·5Bi0·5)TiO3 ceramic: impedance spectroscopy analysis

Polycrystalline sample of (Na0·5Bi0·5)TiO3 was prepared using a high temperature solid-state reaction synthesis at 1070°C and subsequent sintering at 1100°C in oxygen atmosphere. X-ray diffraction (XRD) analysis of (Na0·5Bi0·5)TiO3 powder indicated the formation of a single phase rhombohedral structure. Dielectric study revealed the diffuse phase transition at 340°C. The ac conductivity data were found to obey power law and showed negative temperature coefficient of resistance character. Complex electric modulus analysis indicated non-Debye type dielectric relaxation in the system. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and activation energy of the compound. The correlated barrier hopping model was found to successfully explain the mechanism of charge transport in (Na0·5Bi0·5)TiO3.

Electrical properties of a lead-free perovskite ceramic: (Na0.5Sb0.5)TiO3

Polycrystalline (Na0.5Sb0.5)TiO3 was prepared using a high-temperature solid-state reaction method. An XRD analysis indicated the formation of a single-phase monoclinic structure. Complex impedance studies revealed the presence of grain boundary effects from 300 °C onwards. Also, the dielectric relaxation in the system was found to be of a non-Debye type. The ac conductivity data were used to evaluate the density of states at the Fermi level, the minimum hopping length and activation energy of the compound. The dc electrical and thermal conductivities of grain and grain boundary have been assessed. The correlated barrier hopping model was found to successfully explain the mechanism of charge transport in (Na0.5Sb0.5)TiO3.

Charge transport in Li2B4O7 in single crystal and glassy states

The electrophysical properties of Li2B4O7 single crystals and glasses are studied in the temperature range 290–1100 K and the frequency range 1–1000 kHz. The strong frequency dispersion of ionic conductivity at temperatures close to room temperature is explained by the low-frequency hoppings of lithium ions from the basic to the interstitial positions. The dielectric relaxation accompanying the transport of lithium ions is analyzed within the framework of the Debye-Skanavi model. The minimum hopping length of Li+ ions and the height of the potential barrier between their closest positions are determined. The parameters obtained are compared with the known structural data.