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AC Impedance Spectroscopy, Conductivity and Optical Studies of Sr doped Bismuth Ferrite Nanocomposites
摘要： Effect of Sr doping on the structural, optical, dielectric, impedance properties of citrate combustion reaction route prepared Bi1-xSrxFeO3 (BSFO) nanocomposite has been investigated. The study of Fourier Transform Infrared Spectroscopy confirms the formation of perovskite structure of the Sr doped bismuth ferrite samples. SEM analysis shows decrease in grain size with increasing Sr concentration in BSFO nanocomposite. UV–visible absorption spectra in the spectral range 1.0–3.5 eV showed two doubly degenerate d–d transitions and two charge transfer transitions and optical band gap is found to decrease from 2.14 to 2.05 eV with increasing Sr concentration. Studies of frequency and temperature dependences of dielectric permittivity, impedance and electric modulus of the materials in broad frequency (20 Hz- 1 MHz) and temperature (30o C – 500oC) ranges using a complex impedance spectroscopy technique have provided interesting information on the contribution of the microstructure in these parameters. It has been observed that dielectric constant and dielectric losses decreases as the doping of Sr increased from x=0.1 to x=0.3 and attained a maximum value for BSFO (x = 0.1) sample. Impedance analysis indicates the presence of grain (bulk) and grain boundary resistive contributions which are found to increase with the increased Sr content. The ac conductivity of the samples is found to be frequency and temperature dependent and also vary with extent of Sr doping in BFO. Charge transport through short as well as long range conduction contributions has been indicated in different temperature regions of conductivity studies.
关键词： dielectric response,complex impedance spectroscopy,microstructure,Bismuth ferrite
更新于2025-09-23 15:21:01
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The Origin of Photoinduced Capacitance in Perovskite Solar Cells: Beyond Ionica??toa??Electronic Current Amplification
摘要： Photoinduced capacitances of perovskite solar cells exhibit peculiarities such as an apparently high capacitance and an inductive feature, so-called negative capacitance, which are not easily explained with typical carrier dynamics. Consequently, the origins of the photoinduced capacitances in perovskite solar cells have been intensively debated over the past several years. Here, the photoinduced capacitances of perovskite solar cells are analyzed by impedance spectroscopy. The analysis clarifies that the photoinduced capacitances of perovskite solar cells comprise several Debye relaxation-type capacitance components. Among these components, the photoinduced capacitance in the low-frequency range is attributed to ionic-to-electronic current amplification. However, the photoinduced capacitances in the middle- and high-frequency ranges originate from bipolar injection. The clear elucidation of the origins of the photoinduced capacitances in perovskite solar cells provides comprehensive insights for analyzing properties of perovskites in either the time or frequency domain.
关键词： perovskite solar cells,impedance spectroscopy,ionic to electronic response,negative capacitance
更新于2025-09-23 15:21:01
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Manganese doping stabilizes perovskite light-emitting diodes by reducing ion migration
摘要： Lead halide perovskite light-emitting diodes have recently emerged as high-performance devices. However, they degrade rapidly. This degradation has been attributed to the mixed ionic-electronic nature of these perovskites. Manganese doping increases the stability of perovskite light-emitting diodes, but the effects of manganese doping on ion migration are not well understood. We use impedance spectroscopy and transient ion-drift measurements to study the effect of manganese doping on ion migration in PEABr0.2Cs0.4MA0.6PbBr3 quasi-bulk 2D/3D perovskite light-emitting diodes. We find that manganese doping enhances the activation energy for ion migration two fold and reduces the diffusion coefficient. These changes in the behavior of mobile ions help to explain the improved stability in perovskite light-emitting diodes upon manganese doping and lead to a better understanding of the influence of passivating agents on ion migration and thus on the stability of the devices.
关键词： capacitance,perovskites,manganese,mobile ions,transient ion drift,impedance,light-emitting diodes
更新于2025-09-23 15:21:01
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New approach to detection of guided waves with negative group velocity: Modeling and experiment
摘要： A new method for detecting the forward and backward acoustic waves in the piezoelectric plates by using a system of the acoustically isolated interdigital transducers (IDT) with the different spatial period is developed. This method was tested on the piezoelectric acoustic modes A1 and SH1 propagating in Y-X LiNbO3 plate. Theoretical analysis has shown that the SH1 mode in the entire frequency range represented a forward wave. At that the dispersion dependence of the A1 mode near the cutoff frequency has a smooth transition from a forward wave to a backward one with decreasing frequency. In order to experimentally observe this transition 19 IDTs with different periods were deposited on a single lithium niobate plate. The measurement of the frequency dependence of the real part of the electrical impedance of these IDTs showed that for SH1 mode the resonance frequency decreased monotonically with a growth in the spatial period. This behavior corresponded to a forward wave. For A1 mode the resonance frequency initially decreased with the growth of the IDT period and then began to increase after reaching a value of ZGV frequency. This behavior is explained by the smooth transition from the region of the forward wave to the region of the backward wave. The calculation of the frequency dependences of the real part of the electrical impedance of each transducer for the waves considered, carried out by the finite element method, turned out to be in good agreement with the experiment.
关键词： interdigital transducer,forward and backward plate acoustic wave,phase and group velocities,dispersion dependencies,finite element analysis,electrical impedance
更新于2025-09-23 15:21:01
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Impact of the implementation of a mesoscopic TiO2 film from a low-temperature method on the performance and degradation of hybrid perovskite solar cells
摘要： High efficiencies of over 20% have been reported in the literature for both planar and mesoscopic hybrid perovskite solar cells, and the preferred configuration for scale-up and commercialization is still a matter of debate. The mesoscopic configuration generally requires a high-temperature processing step, which limits applications and makes the process less cost-effective. We have used low-temperature (LT) processing (≤120 °C) to fabricate high-efficiency planar and mesoscopic TiO2-based hybrid perovskite solar cells with comparable performance, highlighted by a champion LT mesoscopic solar cell with 16.2% efficiency. Photovoltaic efficiencies of 14–16% have been achieved for a mesoporous film thickness ranging from 120 to 480 nm by fine-tuning the precursor solution chemistry. The presence of the LT mesoporous layer improves the preservation of performance under conditions of relative humidity of 60%, especially under illumination. Impedance spectroscopy illustrates a similarity of the locus and kinetics of the recombination processes for both configurations. However, inductive loops usually related to ion migration are observed showing different characteristics between both configurations, pointing to the previously suggested correlation between ion migration and degradation. These results suggest that the beneficial role of a mesoporous TiO2 layer might be the stabilization of harmful defects at the perovskite/electron extraction layer interface, and indicate that interface engineering is critical to achieving improved long-term performance.
关键词： Low temperature TiO2,Perovskite solar cells,Impedance spectroscopy,Interfacial degradation
更新于2025-09-23 15:21:01
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Effect of the corona treatment on the microstructure of PVDF probed by electrochemical impedance spectroscopy
摘要： The microstructure of Polyvinylidene Fluoride (PVDF) membrane treated by corona was investigated in this study. The crystalline structure of PVDF membrane was con?rmed by x-ray diffraction (XRD), and the hole structure was evaluated by electrochemical impedance spectroscopy (EIS). It was found that the β phase appears in XRD pattern for treated PVDF, implying the polarization during corona treatment. The variation of membrane resistance suggested that the hole structure of PVDF became more porous with increasing treated time from 0 h to 2 h ?rstly, then became denser with treated time from 2 h to 4 h, and ?nally cracked at the treated time longer than 4 h. All the results indicated that corona treatment would induce the change of the bulk structure of PVDF membrane.
关键词： polyvinylidene ?uoride,corona treatment,electrochemical impedance spectroscopy,hole structure
更新于2025-09-23 15:21:01
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Characterization of Graphite/ZnO Schottky Barriers Formed on Polar and Nonpolar ZnO Surfaces
摘要： The authors demonstrate that the electrical properties of Schottky junctions fabricated by the deposition of colloidal graphite strongly depend on the crystallographic orientation of the ZnO substrate. The current-voltage, capacitance-voltage, and impedance measurements indicate that near-ideal Schottky junctions form on c-plane, while on a- and m-plane the junctions are laterally inhomogeneous. This behavior is assigned to higher concentration of native point defects in the near-surface region of nonpolar ZnO substrates. The authors further present an extended equivalent circuit model, which corresponds to actual structure of the junctions, and sheds light on their electrical transport properties.
关键词： impedance spectroscopy,graphite,equivalent circuit,ZnO,crystal polarity,Schottky contact
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Nano C-V imaging of Semiconductor Devices with Scanning Microwave Impedance Microscopy
摘要： Two doped semiconductor samples are measured using probe-based Scanning Microwave Impedance Microscopy (sMIM). One is a plan-view polished CMOS image sensor and the other is a cross-section polished power device. Both samples are imaged with sMIM using two different approaches: the first using a dual pass method with dC/dV images acquired simultaneously with sMIM during the first pass in contact mode, and the second pass at a fixed offset from the surface. The second method uses a non-resonant mode where C-V are acquired at specific lateral locations. The C-V curves are used to determine polarity compared to dC/dV and also to distinguish p-n junctions, characterize doping concentration, and build images at constant DC values to discern subtle changes not evident in traditional SCM imaging.
关键词： Nano-C-V,SCM,Scanning Probe Microscopy,doping characterization,Scanning Microwave Impedance Microscopy,Scanning Capacitance Microscopy,sMIM
更新于2025-09-23 15:21:01
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One Octave Bandwidth Rectifier With a Frequency Selective Diode Array
摘要： In this paper, a high-efficiency rectifier with one octave bandwidth is proposed by proposing a diode array with a frequency selective topology. With the frequency selective topology, the low-and high-band rectifiers are combined together without extra matching circuit at the input leading to a high-efficiency broadband design. For validation, a prototype rectifier was fabricated and characterized. The measured results show that the RF-dc power conversion efficiency (PCE) maintains above 70% from 1.75 to 3.55 GHz at an input power of 10 dBm. The measured PCE remains more than 50% within 1.4–3.7 GHz and the |S11| is lower than ?10 dB from 1.7 to 3.6 GHz.
关键词： energy harvesting (EH),frequency selection,high efficiency,Broadband RF rectifier,impedance matching,wireless power transfer (WPT)
更新于2025-09-23 15:21:01
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Structural, electrical, dielectric properties and conduction mechanism of sol-gel prepared Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 compound
摘要： A detailed investigation of structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 manganite prepared by the sol-gel method was undertaken. The Rietveld refinement of X-ray diffraction pattern reveals that this compound is indexed in the orthorhombic structure with Pbnm space group. Structural properties are also analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy at room temperature. DC conductivity (σDC) data show the presence of a semiconductor-metal transition at TSM=360K. σDC is described by small polaron hopping model at high temperatures and variable range hopping model at low temperatures. AC conductivity results follow the universal Jonscher's power law at relatively low temperatures and Drude's model at high temperatures. The impedance plots display the contribution of both intra- and inter-granular contributions. Dielectric measurements exhibit highly remarkable dielectric permittivities useful in electronic devices. Dielectric losses are shown to be governed by the DC conduction mechanism and described by the Giuntini theory.
关键词： Electrical properties,Dielectric properties,Metal-semiconductor transition,Impedance spectroscopy
更新于2025-09-23 15:21:01