Search

Propylammonium lead iodide (C3H7NH3PbI3), a promising hybrid perovskite, is successfully synthesized by a solgel technique. Structural, optical, and dielectric properties have been studied in detail. The dielectric constant, loss factor, electric modulus, and AC and DC conductivity of this hybrid perovskite exhibit strong temperature dependence over the frequency range of 10 Hz ≤ f ≤ 8 MHz. The Nyquist plot reveals the distinct contributions of grain and grain boundary to the total impedance. The dielectric constant is found to increase with temperature in the high frequency region. The modified Cole–Cole plot shows that the space charge and free charge conductivity increase with the elevation of temperature, whereas the relaxation time decreases with the rise in temperature. From the modified Kohlrausch–Williams–Watts equation, we perceived asymmetrical nature in electric modulus spectra at various temperatures, which corresponds to the non-Debye type nature of perovskite. It has also been found that, with the elevation of temperature, the imaginary part of electric modulus spectra shifts from the non-Debye type toward the Debye type nature, though failing to acquire exact Debye type response, and emerges as a semiconductor material. AC conductivity of PAPbI3 is illustrated on the basis of the correlated barrier hopping (CBH) mechanism. Activation energy estimated from both modulus spectra and DC conductivity matches well, affirming the similarity between relaxation behavior and conduction mechanism. Along with all these, PAPbI3 possesses a high dielectric constant associated with a small dielectric loss, making it a potential candidate for energy harvesting devices. [ABSTRACT FROM AUTHOR]

The microstructure characterization, optical properties, electrical transport, and dielectric properties of the thermally stable NiAl2O4/Al2O3 nanocomposite powder sample synthesized by the mechanochemical‐assisted solid‐state reaction from the equimolar mixture of NiO and Al2O3 powders are reported. Rietveld refinement, selected‐area electron diffraction pattern, and Fourier‐transform infrared spectrum analyses confirm the formation of a NiAl2O4 spinel phase with a minor Al2O3 phase in the as‐synthesized powder. Transmission electron microscope images reveal the particle size of the powder sample, ≈26 nm. Raman spectrum reveals the presence of NiAl2O4 normal spinel as a major phase in the sample. The temperature and frequency dependence of the dielectric constants of the NiAl2O4/Al2O3 nanocomposite are explained by Koop's phenomenological theory. The electric modulus approach is used to analyze the electrical transport and dielectric relaxation of NiAl2O4/Al2O3 at different temperatures. The electric modulus plot with elevated temperature shows a dielectric loss peak and reflects interesting information on the grains and grain boundaries of the material with varying temperatures. [ABSTRACT FROM AUTHOR]

In this work, CsPbBr3 has been successfully synthesized via sol-gel technique. The orthorhombic phase of the material has been verified by X-ray diffraction measurement followed by Rietveld refinement analysis. Morphological study has revealed the cubic shape of particles with dimension ∼3 μm. Electrical properties are characterized by Complex impedance (Z*), dielectric permittivity (ɛ*), and ac conductivity within the frequency range 10 Hz–5 MHz for different temperatures between 313K and 673 K. The dielectric behavior of CsPbBr3 is found to be thermally activated and frequency dependent. The ascensive nature of ɛ′(ω) at lower frequency is assigned to the Maxwell-Wagner type interfacial polarization. ɛ′(ω) has been fitted using Kramers-Kronig relation by including the dielectric constant at infinite frequency. Variation of ɛ″(ω) with frequency has been explained by the hopping of charge carrier over a potential barrier between charge defects. AC conductivity has also been fitted by Jonscher's power law to find the real component of conductivity and it has been described by using the Jump relaxation model. Activation energy has been calculated by fitting the dc conductivity using Arrhenius relation and found to have a value of 0.517 eV. Grain resistance (rg), grain capacitance (cg), grain boundary resistance (rgb), and grain boundary capacitance (cgb) have been accounted by fitting Z′ vs log(f) plot with equivalent circuit and existing theoretical model. [ABSTRACT FROM AUTHOR]

In this work, methylammonium bismuth iodide [(CH3NH3)3Bi2I9] has been synthesized through the mechanochemical process. Indeed, (CH3NH3)3Bi2I9 emerges as promising alternative to lead-based inorganic–organic perovskite due to low toxicity and better stability. X-ray diffraction spectra reveal monoclinic structure of (CH3NH3)Bi2I9 with space group C2/c. Kubelka–Munk method is conducted to compute the bandgap (2.16 eV). The impedance and dielectric properties of (CH3NH3)3Bi2I9 have been investigated within frequency range of 4 Hz to 1 MHz for several temperatures in between 333 to 453 K. The complex impedance spectroscopy has analyzed by fitting the Cole–Cole plot with suitable grain and grain boundary contributions (rg, rgb). Conductivity and electric modulus spectra have been analyzed to enlight the shaded portion of transportation properties. The scaled coordination of modulus spectrum merges in a single master curve which signifies that the distribution of relaxation time is temperature independent. To compute the DC conductivity, AC conductivity data have fitted using Jonscher's power law. The activation energy calculated from Arrhenius plot is 0.477 eV. [ABSTRACT FROM AUTHOR]

MAPbX3(MA = CH3NH3, X = Br, I) are synthesized by the chemical route. The Rietveld refinement of the room temperature X-ray diffraction pattern of the materials shows that MAPbBr3is crystallized in the cubic Pm3m crystal symmetry whereas MAPbI3crystallizes in the tetragonal phase with space group I4/mcm. The dielectric relaxation of MAPbX3has been studied in the frequency range from 42 Hz to 0.2 MHz in the electric modulus formalism. The relaxation time is determined by the reciprocal of the frequency where the maximum of the imaginary part of the electric modulus is centred. The relaxation mechanism of the samples is investigated by the Cole-Cole model. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a capacitance. The frequency dependent conductivity spectra follow the power law. [ABSTRACT FROM AUTHOR]

Abstract Cesium lead iodide (CsPbI 3) has been prepared by a new experimental hazard free precipitation technique. X-ray diffraction spectra have been interpreted with Rietveld refinement which assures the orthorhombic phase of CsPbI 3. Energy dispersive X-ray fluorescence spectra confirms the formation of ternary compound. Orthorhombic to cubic phase transition has been studied by observing hysteresis loop in R(T)-T plot for forward-reverse temperature scan. The intra-grain and inter-grain contribution of CsPbI 3 to dielectric relaxation has been accounted by fitting the complex impedance plot (Cole-Cole plot). The value of FWHM in Z″(ω)-lnf or M″(ω)-lnf plot is greater than 1.141 decades which reveals the non-Debye type relaxation within material. The broad relaxation peak signifies that there is a distribution of relaxation time over a mean value. Moreover, Z″ & M″ have been plotted in scaled coordinate to check whether the distribution of relaxation time is temperature dependent or not. The frequency dependent relative permittivity represents the decreases of polarizations with frequency which have been successfully analyzed by Koop's theory. Here, activation energies are equal for different formalism, suggests that the same type charge carriers involved in conduction as well as relaxation process. Ac conductivity has been interpreted by using Jonncher's power law and frequency exponent (n) increases with temperature which suggests the presence small polaron hopping mechanism. [ABSTRACT FROM AUTHOR]

In this work, CsPbBr3 has been successfully synthesized via sol-gel technique. The orthorhombic phase of the material has been verified by X-ray diffraction measurement followed by Rietveld refinement analysis. Morphological study has revealed the cubic shape of particles with dimension ∼3 μm. Electrical properties are characterized by Complex impedance (Z*), dielectric permittivity (ɛ*), and ac conductivity within the frequency range 10 Hz–5 MHz for different temperatures between 313K and 673 K. The dielectric behavior of CsPbBr3 is found to be thermally activated and frequency dependent. The ascensive nature of ɛ′(ω) at lower frequency is assigned to the Maxwell-Wagner type interfacial polarization. ɛ′(ω) has been fitted using Kramers-Kronig relation by including the dielectric constant at infinite frequency. Variation of ɛ″(ω) with frequency has been explained by the hopping of charge carrier over a potential barrier between charge defects. AC conductivity has also been fitted by Jonscher's power law to find the real component of conductivity and it has been described by using the Jump relaxation model. Activation energy has been calculated by fitting the dc conductivity using Arrhenius relation and found to have a value of 0.517 eV. Grain resistance (rg), grain capacitance (cg), grain boundary resistance (rgb), and grain boundary capacitance (cgb) have been accounted by fitting Z′ vs log(f) plot with equivalent circuit and existing theoretical model. [ABSTRACT FROM AUTHOR]

Abstract A simple mechanical alloying process has been implemented to obtain cerium oxide nanocrystallites monodoped with transition metal element (Mn). The microstructural, compositional and crystallographic information are investigated by employing Rietveld refinement using X-ray diffraction (XRD) data, energy dispersive X-ray (EDX) pattern and analyzing high resolution transmission electron microscopy (HRTEM) images. The results reveal that the sample exhibits a single phase cubic fluorite-type Ce 0.95 Mn 0.05 O 2-δ structure. Rietveld analysis shows the coexistence of Ce3+ and Ce4+ ions in the sample. HRTEM image reveals the sheer plastic deformation on lattice planes. The frequency and temperature dependent electrical behavior of the undoped, Mn-doped and sintered samples are analyzed by impedance spectroscopy, dielectric relaxation and ac conductivity studies. The correlated barrier hopping (CBH) model has well explained the ac conduction mechanism. The release of electrons during the reduction of Ce4+ and/or Mn4+ ions to Ce3+ and/or Mn3+/Mn2+ ions by the exclusion of excess oxygen in the lattice are responsible for the electronic conductivity of the samples. The activation energy of the sintered sample is estimated both from relaxation and hopping processes and the estimated values ascertain that the charge carrier hopping process in the samples is accompanied by the dielectric relaxation. Graphical abstract Image 1 Highlights • Mechanochemically synthesized single phase cubic fluorite-type Ce 0.95 Mn 0.05 O 2-δ. • Rietveld analysis indicates the coexistence of Ce3+ and Ce4+ ions in the sample. • HRTEM image reveals the sheer plastic deformation on lattice planes. • Impedance spectroscopy reveals the dominance of grains than grain boundaries. • AC conductivity explained with the correlated barrier hopping (CBH) model. [ABSTRACT FROM AUTHOR]

• Better thermal stability in propylammonium based hybrid perovskite. • Larger organic cation induces lesser ionic migration in Propylamonium lead bromide. • Details analysis of dielectric properties shows giant dielectric constant. • Self-biased UV detector with excellent spectral selectivity using this material. This work contains an extensive study on temperature dependent complex dielectric behavior over 4 Hz ≤ f ≤ 8 MHz of a promising hybrid perovskite, propylammonium lead bromide. The structural, as well as morphological property of this sol-gel derived sample have been analyzed with the help of XRD and SEM respectively. The obtained energy band gap and thermal stability study ensure the capability of this material in device fabrication. Possessing a wide band gap, this perovskite fascinatingly serves as a UV photodetector. The individual impact of grain and grain boundary over the entire resistance has been resolved by Maxwell – Wagner Cole–Cole model. This material holds an amazing property; giant dielectric constant near room temperature at low frequency limit which escalates rapidly in the influence of thermal effect. Modified cole – cole plot assures that both space and free charge conductivities ascend with temperature. The asymmetrical nature of the imaginary part of electric modulus is analyzed by Kohlrausch – Williams – Watts which confirms its non – Debye nature diminishes with rising temperature. The thermally triggered AC conductivity follows Jonscher's power law and is emphasized with the jump relaxation model. The bulk conductivity of the sample depends on temperature and is elucidated with variable range hopping of localized charge carriers. Activation energy plays a key role in the ionic conduction mechanism within the sample, described elaborately. The overall substantial studies on its application as UV detector and different dielectric properties of this sample construct the basis of appreciable acceptability of the sample in energy harvesting. [ABSTRACT FROM AUTHOR]