Temperature Dependence Of Ac Conductivity Research Articles

Development of High-Performance Polyindole/Silicon Carbide Nanocomposites for Optoelectrical and Sensing Applications.

In this study, silicon carbide (SiC)-reinforced polyindole (PIn) nanocomposites were prepared by a simple in situ polymerization method. The successful reinforcement of the nanofiller within the host matrix was characterized using different analytical techniques. The chemical bonding of SiC in the polymer was identified by the characteristic peak around 800 cm1 using Fourier transform infrared spectroscopy (FT-IR). The increment in intensity of the absorption and enhanced crystallinity of the samples upon the addition of nanofillers were analyzed using UV-vis spectroscopy and X-ray diffraction (XRD). The prepared specimens showed reduced optical bandgap energy (3.188 eV) and Urbach energy (2.315 meV) with an improved refractive index (2.348). The effect of nanoparticles on the surface morphology of the nanocomposites was studied using scanning electron microscopy (SEM), and a uniform dispersion of fillers in the matrix was found for PInSiC7. A high-resolution transmission electron microscopy (HR-TEM) revealed the shape and average particle size of the sample. X-ray electron spectroscopy (XPS) measurements confirmed the formation of the nanocomposite by exhibiting the presence of all elements in the corresponding spectra. The thermal stability and glass transition temperature of the nanocomposites were significantly improved with the addition of SiC. The temperature-dependent AC conductivity, dielectric parameters, complex impedance, and electrical modulus were also evaluated using an impedance analyzer. The increased electrical characteristics of the PInSiC7 sample can be attributed to the uniform spread and strong synergetic interaction of SiC with PIn. The results thus showcased the potential of the samples for use in optical and energy storage applications. This study was also extended to understand the ammonia sensing properties, which make it possible to design and develop gas sensors using the PInSiC nanocomposites.

Magnetoelectric Properties of Aurivillius-Layered Perovskites

In the present work, we have synthesized rare-earth ion modified Bi4−xRExTi2Fe0.7Co0.3O12−δ (RE = Dy, Sm, La) multiferroic compounds by the conventional solid-state route. Analysis of X-ray diffraction by Rietveld refinement confirmed the formation of a polycrystalline orthorhombic phase. The morphological features revealed a non-uniform, randomly oriented, plate-like grain structure. The peaks evident in the Raman spectra closely corresponded to those of orthorhombic Aurivillius phases. Dielectric studies and impedance measurements were carried out. Asymmetric complex impedance spectra suggested the relaxation of charge carriers belonging to the non-Debye type and controlled by a thermally activated process. Temperature-dependent AC conductivity data showed a change of slope in the vicinity of the phase transition temperature of both magnetic and electrical coupling natures. Based on the universal law and its exponent nature, one can suppose that the conduction process is governed by a small polaron hopping mechanism but significant distortion of TiO6 octahedral. The doping of the A-sites with rare-earth element ions and changes in the concentrations of Fe and Co ions located on the B-sites manifested themselves in saturated magnetic hysteresis loops, indicating competitive interactions between ferroelectric and canted antiferromagnetic spins. The magnetic order in the samples is attributed to pair-wise interactions between adjacent Fe3+–O–Fe3+, Co2+/3+–O–Co3+/2+, and Co2+/3+–O–Fe3+ ions or Dzyaloshinskii–Moriya interactions among magnetic ions in the adjacent sub-lattices. As a result, enhanced magnetoelectric coefficients of 42.4 mV/cm-Oe, 30.3 mV/cm-Oe, and 21.6 mV/cm-Oe for Bi4−xDyxTi2Fe0.7Co0.3O12−δ (DBTFC), Bi4−xLaxTi2Fe0.7Co0.3O12−δ (LBTFC), and Bi4−xSmxTi2Fe0.7Co0.3O12−δ (SBTFC), respectively, have been obtained at lower magnetic fields (<3 kOe). The strong coupling of the Aurivillius compounds observed in this study is beneficial to future multiferroic applications.

Studies on structural, dielectric, electrical, and ferroelectric properties of the polycrystalline NaBiFe2O5

Synthesis (via solid-state reaction) and characterization (structure, microstructure, dielectric, electrical, and ferroelectric behavior) of brownmillerite polycrystalline material NaBiFe2O5 (NBFO) are discussed in this paper. The formation of a triclinic structure has been analyzed by the X-ray diffraction method. The morphology of the ceramic sample was analyzed using a field emission scanning electron microscope (FESEM) and energy-dispersive X-ray analysis (EDX). It is found that the grains are uniformly distributed through well-defined grain boundaries of the sample containing all the constituent elements (Na, Bi, Fe, and O). The study of both frequency (1 kHz–1MHz) and temperature (25–450 °C) dependent dielectric and AC-conductivity predicts the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism of NBFO. The impedance spectra support the semiconducting behavior of the brownmillerite NBFO at high temperature. The resistance of the material falls with a rise in temperature favors the negative temperature coefficient resistance behavior of the material. The study of electric polarization suggests the possibility of the ferroelectric properties of the studied sample. The high dielectric constant and low tangent loss suggest the possibility of the material for device applications.

Studies of structural, dielectric, electrical, and optical properties of a multi-doped novel complex perovskite (Bi1/2Na1/2)(Fe1/3Mn1/3W1/3)O3 ceramic for opto-electronic application

(Bi1/2Na1/2)(Fe1/3Mn1/3W1/3)O3 is a new complex perovskite compound synthesized by a solid-state method. A preliminary structural study using the X-ray diffraction (XRD) pattern shows the monoclinic symmetry of the material. The scanning electron microscope (SEM) micrograph shows the dense microstructure or morphology of rectangular shape grains of different dimensions. The purity and elemental composition of the compound were obtained by energy dispersive X-ray (EDX and EDS) spectrum. The analysis of frequency and temperature-dependent relative dielectric constant (εr) impedance and ac conductivity (σac) predict the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism. In-depth analysis of impedance and associated factors reveals that they are substantially dependent on temperature and have a significant link with their microstructures. Similar to semiconductors, the nature of impedance spectra displays a negative temperature coefficient of resistance behavior. The electric polarization hysteresis loop shows the ferroelectric behavior and explores the possible applications. The band gap (Eg) is found to be 2.40 eV using the UV-visible spectrum, appropriate for solar and optoelectronic applications. The value of super-capacitance is 58.96 F/g, applicable for an electrode material supercapacitor application. The behavior of leakage currents has also been investigated and found that conduction has been identified as a space-charge conduction mechanism. We are very interested in designing and manufacturing novel dielectric ceramics because of the rising need for the miniaturization of electronic components and the flexibility of applications. Sensors, actuators, transducers, and capacitors are among the most prevalent applications of such types of materials.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Optical, structural and dielectric properties of solvothermally grown molybdenum sulfide nanosheets

MoS2 nanosheets have been synthesized by simple and conventional solvothermal methods. FEG-TEM images reveal that the produced MoS2 sample has a hexagonal crystal structure with large (2μm) nanosheets. The XRD and Raman spectra of the samples also confirm the hexagonal crystal phase. The schematic refined unit cell with electron density mapping is visualized after Rietveld refinement. The optical properties such as absorbance, PL, refractive index, extinction coefficient, dielectric constant, optical conductivity, etc. have been investigated in the wavelength range of 330nm to 1000nm. The normal dispersion (ND) and the anomalous dispersion (AD) regions have been observed in the refractive index spectrum. The estimated carrier concentration has been found to be 5×104cm−3. The temperature-dependent indirect bandgap of MoS2 has been simulated using a semi-empirical formula based on electron-phonon coupling and it decreases with increasing temperature. The calculated average lifetime of carriers is 1.17 ns. The grown MoS2 shows large dielectric constant and low tangent loss in the frequency range of 5–500 kHz. The Nyquist plot of the sample gives the NTCR (negative temperature coefficient of resistance) behaviour like a semiconductor. The activation energy (EA) has been estimated from temperature dependence AC conductivity.

Structural, Optical, Electrical, and Electrochemical properties of ZnMoO4 microspheres synthesized by the twin crystal method

A mixed metal oxide, ZnMoO4 has been prepared by the conventional solid-state reaction method, with the help of hydrothermally synthesized solvents of ZnO and MoO3. The phase purity and surface morphology of the precursors of ZnO and MoO3 are resolved with the Rietveld refinement and scanning electronic microscopy studies. Structural, morphological, and vibrational modes characterizations associated with the unit cell information of ZnMoO4 are explained by Rietveld's refined technique of XRD, SEM, and Raman studies, respectively. The anode solvent ZnMoO4 is subjected to cyclic voltammetry analysis. Hence, the electrochemical impedance spectroscopy (EIS) measurements are recorded between 3.0 and 0.01 V at a scan rate of 0.5 mV s−1 for ZnMoO4 electrodes as an anode material in LIBs. Here, it has been noticed that the hexagonal-like ZnMoO4 has high capacity and reasonable cycle stability compared with ordinary ZnMoO4. An anomalous change in permittivity and tangent loss at Tθ =750K in temperature dependent dielectric studies confirm phase transition due to the transformation of molecular groups, MoO4 (low temperature) triclinic phase into molecular groups, MoO6 (high temperature) monoclinic phase. The temperature and frequency dependent AC-conductivity at different intervals reveal mechanisms associated with different temperature regions. This study provides an in-depth understanding of the electrical and electrochemical activities of zinc molybdate anode materials in novel applications.

Effect of interfacial layers on the temperature-dependent dielectric and impedance behavior of flexible PVDF-BST nanocomposite thick films

High energy storage performance of polymer-ceramic nanocomposites at elevated temperatures (room temperature to 100 °C) becomes unstable because of thermally unstable dielectric behavior (permittivity and loss tangent). Therefore, the present work describes the experimental and analytical investigation of the temperature-dependent dielectric behavior, AC conductivity, and impedance of flexible poly(vinylidene difluoride) (PVDF)-Ba0.8Sr0.2TiO3 (BST) nanocomposite thick films. An increase in the dielectric constant and a decrease in the loss tangent is found with an increase in the loading of BST nanoparticles in the nanocomposite thick films. The highest dielectric constant, approximately 25, and the lowest loss tangent, approximately 0.03, are observed for 10 wt% BST–loaded PVDF-BST nanocomposite at 1 kHz; the dielectric constant and the loss tangent increase to approximately 93 and approximately 1.64, respectively, at 150 °C. The dielectric constant and the loss tangent of all the PVDF-BST nanocomposites are thermally stable up to 70 °C, and then increase with further increase of the temperature. A phenomenological model is proposed to explain the experimentally observed behavior, which might be attributed to the thermally induced translational motion in the polymeric chains of PVDF, the motion of ions, and the migration of space charge in the interfacial layer of the PVDF matrix and BST nanoparticles.

Effect of sintering time on electrical, ferroelectric, and piezoelectric performances of microwave synthesized sodium bismuth titanate ceramics

Herein, we report the synthesis of sodium bismuth titanate (Na0.5Bi0.5TiO3/NBT), a lead-free ceramic prepared via a cost and time-effective microwave synthesis route. This work presents the investigation of microstructural, electrical, and optical characteristics of NBT ceramics. The formation of a single-phase NBT sample sintered for 30 and 40 min (denoted as NBT 30 and NBT 40) is confirmed by Rietveld refinement and Raman measurement. FTIR spectroscopy is used to characterize the single-phase nature and to confirm the presence of desired vibrational spectra in the perovskite structure. Tightly packed micron-sized grains are observed from the field emission scanning electron microscopy. Due to the A-site disorder present in the lattice, two diffuse types of dielectric anomalies are present in the temperature-dependent dielectric plot for both samples. The maximum dielectric constant values of 1475 and 1628 are found for NBT 30 and NBT 40 samples at the transition temperature. From temperature-dependent AC conductivity measurement, NBT 40 samples show a higher value of conductivity in comparison to NBT 30. The PE hysteresis loops confirm the ferroelectric character present in both samples. An improved piezoelectric coefficient is observed with increasing sintering time and is found to be 80 pCN−1 for NBT 40. The optical bandgap of materials is 3.03 and 3.1 eV for NBT 30 and NBT 40, respectively.

Comprehensive studies on the electrical transport of some chalcogenide semiconductors: frequency- and temperature-dependent AC conductivity

The AC conductivity of chalcogenide semiconductors doped with Ag2S was extensively studied, not only for applications in devices but also for academic interests. X-ray diffraction studies reveal the presence of GeS, Ag2S, Se5.1S1.9, Se2.57S5.43, Ag2Se, S3Se5, Se4.7S3.3, and Ag8S nanocrystallites. The characteristic vibration that appeared in the range 500–600 cm−1 is due to the Ag–S bond, and the vibrations at 3,700 and 1600 cm−1 can be assigned as the bending and stretching vibrations of the O–H bond, which may be formed due to the adsorption of H2O molecules on the Ag2S surface. DC electrical conductivity can be increased by optical phonon frequency, which may be involved in the enhancement of structural vibrations. At low temperatures, the “density of states” increases from 3.337 × 1019 to 2.396 × 1021 eV−1 cm−3, and at high temperatures, it enhances from 3.417 × 1028 to 1.1356 × 1031 eV– 1 cm−3. The correlated barrier hopping model explores the maximum barrier height for composition, x = 0.1 as 0.0292 eV. The modified non-overlapping small polaron tunnelling model reveals the polaron transfer activation energy for x = 0.2 as 0.09110 eV. The independence of the electrical relaxation process of the system on temperature and its dependence on composition were exhibited by the scaling of the conductivity spectra.

Low-frequency electrical response related to oxygen vacancies in Al3+ substituted M-type hexaferrite

The presence of oxygen vacancies is unavoidable in many complex metal oxide materials such as hexaferrites. This article investigates the role of crystal defects, such as oxygen vacancies, and different oxidation states of Fe ions, on the electrical conduction behaviors of Al3+ substituted Ba0.4La0.1Sr0.5Al x Fe12−x O19 hexaferrites by analyzing the temperature dependent AC impedance and AC conductivity. The optimal substitution of La3+ ions and high-temperature sintering is responsible for forming oxygen vacancies while reducing Fe from Fe3+ to Fe2+ cations, as observed in structural and XPS analysis, which affects electrical conduction behaviors. The departure from ideal Debye-type relaxation behavior is also one of the effects of crystal defects. Temperature variation of relaxation time shows a sharp change at around 403 K. This may be due to different electrical entities influencing the mode of electron hopping with temperature. The activation energy calculated from the temperature dependent relaxation time confirmed the presence of electron hopping through the bridging effects of the first ionization of oxygen vacancies Fe2+––Fe3+ below a temperature of 403 K. Above 403 K, electron hopping through different oxidation states of Fe3+ + e− → Fe2+ and migration of oxygen vacancies toward the bulk surface are responsible for the conduction mechanism. The DC resistivity and AC conductivity show that the bridging effects of oxygen defects can also induce Coulomb interaction between the defect sites resulting in Efros–Shklovskii variable range hopping and correlation barrier hopping below 403 K. Above 403 K, polaron-assisted electron hopping is more desirable, as confirmed by the non-overlapping small polaron tunneling model.

Investigation of dielectric relaxor-like anomaly behaviour of non-ferroelectric BaZrO3 polycrystalline ceramic

The dielectric responses and ac conductivity of non-ferroelectric BaZrO3 polycrystalline ceramic were examined in the wide ranges of frequency and temperature. The colossal dielectric behaviour was detected in the dielectric spectra, accompanied by two relaxor-like anomalies. The activation energy associated with the relaxor behaviour at low temperature regions was estimated to be 0.85 eV. The bulk relaxation and Maxwell-Wagner relaxation effect are responsible for the oxygen-vacancy induced pseudo-relaxor behaviour at low-temperature dielectric anomalies. The dielectric anomaly at 585 °C was confirmed to be a paraelectric to ferroelectric phase transition induced by the process of disordered to ordered state of oxygen vacancies. A modified empirical Cole-Cole model was proposed to explain the frequency-dependent permittivity and dielectric loss spectra. The two humps at low and high-temperature regions associated with oxygen-vacancy induced pseudo-relaxor and paraelectric to the ferroelectric phase transition, respectively, were observed in the temperature-dependent ac conductivity study.

Investigation on Temperature-Dependent Electrical Transport Behavior of Cobalt Ferrite (CoFe2O4) for Thermistor Applications

This paper discusses the temperature and frequency-dependent dielectric and electrical transport properties of cobalt ferrite (CoFe2O4) and its suitability for thermistor applications. The material is prepared through a high-temperature solid-state reaction route. The formation of the materials is checked by using an X-ray diffraction. Microstructure study is done through SEM analysis. Analysis of dielectric data shows a thermally activated relaxation process occuring in the material within the studied frequency range. Analysis of complex impedance (Nyquist) plots at different temperatures reveal the contribution of grain to the overall electrical response of the compound. The variation of dc conductivity with temperature shows the NTCR behavior of the material. Looking into the strong dependence of resistivity on temperature, the thermistor parameters are evaluated using the grain resistance at different temperatures, which suggest the possible application for thermistor-based devices as well as a temperature sensor. The temperature-dependent ac conductivity (σ ac) fits well with Jonscher’s universal power law. The activation energy calculated from the temperature-dependent spectroscopic plots of impedance and conductivity suggests the charge carriers involved in deciding transport properties.

Investigation on ferroelectric, dielectric and pressure sensing properties of samarium substituted lead magnesium niobate-lead titanate oxide

In the last several decades, researchers have been developing hydraulic pressure sensors suitable in harsh oil mediums with high figures of merit. A well-known columbite method is used to prepare a series of phase pure electroceramics Pb(1-1.5y)Smy[(Mg1/3Nb2/3)1-xTix]O3 (Sm(y)-PMN(x)PT) with x = 0.20, 0.30; and y = 0.010, 0.025 for possible applications as hydraulic pressure sensors. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to study the crystal structure, microstructure, and morphology of the sintered ceramics. The frequency and temperature-dependent dielectric and ac conductivity analyses were performed over a temperature range of 300–480 K to understand the phase stability and phase transition temperatures. Room temperature (297 K) polarization-electric field and PUND analysis confirmed the large polarization (∼30–40 μC/cm2) in the investigated compositions. The hydrostatic pressure-dependent relative capacitance change was examined using a lab-made setup for different compositions for the pressure varying from 0 to 50 MPa. The percentage sensitivity varies with samarium and titanium compositions that range from 0.078 MPa−1 to 0.197 MPa−1. The highest relative change in capacitance was obtained for Pb0.963Sm0.025[(Mg1/3Nb2/3)0.80Ti0.20]O3 (Sm0.025-PMN0.20PT) ceramic with percentage sensitivity 0.197 MPa−1, nearly double to our earlier report on Pb[(Mg1/3Nb2/3)0.7Ti0.3]O3 composition. The improvement in sensitivity may be due to inherent properties, such as slim hysteresis, low tangent loss (∼0.002–0.1), large change in phase transition temperature (∼25 K) due to dielectric dispersion and relaxor-like nature compared to other investigated systems.

STUDY OF STRUCTURAL AND TRANSPORT PROPERTIES OF CuFe2O4 SYNTHESISED VIA LOW COST SOLID STATE REACTION ROUTE

ABSTRACT The ceramic compound CuFe2O4 was synthesised via conventional high-temperature solid-state reaction route. The structural study of the compound was done using X-ray diffraction technique. The preliminary structural study was performed using POWD software and a tetragonal structure was suggested. The Rietveld refinement of XRD (X-ray Diffraction) data was carried out using FullProf software and the refined lattice parameters were obtained as a = 5.80030 Å and c = 8.69400 Å with high tetragonality ratio. The crystallite size and lattice strain were calculated using Williamson–Hall (W-H) plot. The temperature and frequency dependent electrical properties of this compound are analysed using complex impedance technique. The impedance and modulus study of the compound showed the contribution of intra-grain effect to the overall electrical response. The studied ceramic possessed a non-Debye-type relaxation mechanism. The bulk resistance decreased with the increase in temperature, thus showing negative temperature coefficient of resistance behaviour. Modulus and conductivity study showed the evidence of conduction via hopping mechanism inside the material. Frequency-dependent AC conductivity followed Jonscher’s universal power law. The Arrhenius equation was fitted with the temperature-dependent AC conductivity at different frequencies, and activation energies were determined to understand the charge species involved in the conduction mechanism.

Influence of ionic radii on the conduction mechanism in lanthanum silicate oxyapatite

Lanthanum Silicate oxyapatite has attracted researchers due to its interesting ion channels and conduction pathways. In the present work, the average ionic radii of La site are altered via substitution of La3+ with Ba2+ and Ca2+ to form (La1-xAx)9.67(SiO4)6O2+δ (x = 0.0, 0.05, 0.10 and 0.15) where A = Ca and Ba. Further, the ionic radii of substituents will alter the average area of critical triangle (saddle point). Therefore, it is expected to affect the ion mobility. The single-phase Ca and Ba substituted samples are observed and Rietveld refinement suggests no phase change with the ionic radii. The elemental content obtained from Rietveld refinement, Energy dispersion spectra, X-ray photoelectron spectroscopy and thermogravimetric analysis suggests La deficiency in Ca substituted sample and O deficiency in Ba substituted sample. Temperature and frequency dependent ac conductivity in the temperature range (548 K–973 K) suggests that the conductivity is higher at x = 0.05 than x = 0.1 in Ba substituted sample. On a comparative note, the conductivity is higher in Ca substituted sample than that of the Ba substituted sample for x = 0.1.

Elucidating Polaron Dynamics in Cs2AgBiBr6 Double Perovskite.

Lead-free Cs2AgBiBr6 double perovskites have recently emerged as a possible alternative to lead-based halide perovskites for photovoltaic and optoelectronic applications. Significant research efforts have been devoted toward device engineering to enhance the performance of Cs2AgBiBr6 double-perovskite-based photovoltaic and optoelectronic devices; however, less attention has been paid to address their intrinsic photophysical properties. In this work, we have shown that the small polaron formation under photoexcitation and polaron localization limits the carrier dynamics in Cs2AgBiBr6 double halide perovskites. Furthermore, temperature-dependent ac conductivity measurement reveals that single polaron hopping is the dominant conduction mechanism. Ultrafast transient absorption spectroscopy reveals that a deformed lattice under photoexcitation leads to the formation of small polarons which act as self-trapped states (STSs) and lead to the ultrafast trapping of charge carriers. Our findings provide an in-depth understanding of intrinsic limitations of Cs2AgBiBr6 perovskites, which can be applicable for other bismuth-based semiconductors.

Investigation of conduction mechanism and UV light response of vertically grown ZnO nanorods on an interdigitated electrode substrate.

Vertically aligned zinc oxide nanorod (ZnO-NR) growth was achieved through a wet chemical route over a comb-shaped working area of an interdigitated Ag-Pd alloy signal electrode. Field-emission scanning electron microscopy images confirmed the formation of homogeneous ZnO-NRs grown uniformly over the working area. X-ray diffraction revealed single-phase formation of ZnO-NRs, further confirmed by energy-dispersive X-ray spectroscopy analysis. Temperature-dependent impedance and modulus formalisms showed semiconductor-type behavior of ZnO-NRs. Two electro-active regions i.e., grain and grain boundary, were investigated which have activation energy ∼0.11 eV and ∼0.17 eV, respectively. The conduction mechanism was investigated in both regions using temperature-dependent AC conductivity analysis. In the low-frequency dispersion region, the dominant conduction is due to small polarons, which is attributed to the grain boundary response. At the same time, the correlated barrier hopping mechanism is a possible conduction mechanism in the high dispersion region attributed to the bulk/grain response. Moreover, substantial photoconductivity under UV light illumination was achieved which can be attributed to the high surface-to-volume ratio of zinc oxide nanorods as they provide high density of trap states which causes an increase in the carrier injection and movement leading to persistent photoconductivity. This photoconductivity was also facilitated by the frequency sweep applied to the sample which suggests the investigated ZnO nanorods based IDE devices can be useful for the application of efficient UV detectors. Experimental values of field lowering coefficient (βexp) matched well with the theoretical value of βS which suggests that the possible operating conduction mechanism in ZnO nanorods is Schottky type. I-V characteristics showed that the significantly high photoconductivity of ZnO-NRs as a result of UV light illumination is owing to the increase in number of free charge carriers as a result of generation of electron-hole pairs by absorption of UV light photons.

Understanding the polaron behavior in Cs2CuSbCl6 halide double perovskite.

Lead-free halide double perovskites A2MM'X6 (A = Rb+, Cs+, etc.; M = Ag+, K+, Li+; M' = Sb3+, In3+ or Bi3+ and X = I-, Br- or Cl-) have recently been suggested as an alternative to lead-based halide perovskites for optoelectronic and photovoltaic applications. While a great deal of effort has been put into device engineering to improve the performance of photovoltaic and optoelectronic devices that are based on A2MM'X6 double perovskites, there has been relatively little attention given to their inherent photophysical properties. The current research demonstrates that small polaron formation under photoexcitation and polaron localization limit the carrier dynamics in the Cs2CuSbCl6 double halide perovskite. In addition, temperature-dependent AC conductivity measurements indicate that single polaron hopping is the primary conduction mechanism. The ultrafast transient absorption spectroscopy results revealed that the formation of small polarons, which function as self-trapped states (STSs) and result in the ultrafast trapping of charge carriers, are caused by a distorted lattice under photoexcitation. These findings provide a thorough understanding of the intrinsic restrictions of Cs2CuSbCl6 perovskite and could have relevance for other antimony-based semiconductors.

Conduction and Dielectric Behaviors of Ge16Se52Te32-xSbx(x = 0,2,4,6,8) glassy system

The quaternary antimony substituted Ge-Se-Te glasses have been synthesized using melt quench technique. The ac conductivity and dielectric properties viz. dielectric constant and dielectric loss of pallets has been studied in the frequency range (500Hz-1MHz) from room temperature to 365K. Both ac conductivity and dielectric properties are found to have dependence on frequency and temperature. The ac conductivity is found to obey the power law ωs, where s approaches unity at room temperature and decreases with increase in temperature. The temperature dependence of ac conductivity has been explained on the basis of relaxation caused by the motion of electrons or atoms and the correlated barrier hopping (CBH) model. The dielectric constant and dielectric loss are found to increase with temperature and decrease with the frequency. The variation of the studied properties with Sb content has also been investigated for all the compositions.