Variation Of Dielectric Constant Research Articles

A Theoretical Approach to Study the Frequency Dependent Dielectric behavior of Breast Cancer Cells using AlN buffer-based AlGaN/GaN HEMT

Abstract This article investigates the applicability of open gated high electron mobility transistor (HEMT) as a biosensing platform for Breast cancer detection. The present study reports the detection of healthy (MDA-10) and malignant cells (MDA-MB-231) associated with breast cancer using high-quality AlN buffer AlGaN/GaN HEMT with dual cavity structure formed by etching out the gate metal from source and drain sides under the gate region. The AlN buffer AlGaN/GaN HEMT provides better 2DEG confinement and large conduction band offset than GaN buffer. The proposed design is analyzed at frequencies of 900 MHz and 10 GHz, as breast cells have distinct dielectric properties at different microwave frequencies. The variation in dielectric constant of the cavity region corresponding to biomolecular species will change the device’s electrical characteristics and hence can be used to detect breast cancer cells. In this work, the device sensing parameters considered for analysis are shift in threshold voltage and drain current sensitivity. The device performance has also been analyzed by optimizing cavity thickness and length to select the best design for the sensing. The effect of non-ideal conditions such as steric hindrance and probing is also studied by emulating these real time effects in simulation. The device shows a maximum drain current sensitivity of 29.94% for 20 nm of cavity thickness and 1µm of the cavity length. The results depict that the proposed device design exhibits a highly sensitive response and can be promising alternate for future biosensing applications.

The growth aspects and experimental techniques for the characterization of amino acid L-histidine hybrid crystals for nonlinear optical device applications

The development of crystal growth and measurement methods opens new possibilities for studying materials with remarkable nonlinear optical features. The development of bulk crystals is a constant concern to be beneficial for device applications. This study focuses on the development of nonlinear optical crystals of l-histidine complexes, characterization approaches, and prospective applications. The solution growth approach, a straightforward, inexpensive, and low-temperature growth technique, was adopted broadly. Recent studies show that l-histidine derivatives have potential optical, SHG, thermal, dielectric, and mechanical properties, making them an excellent choice for nonlinear optical devices. In this work, structural, spectroscopic, chemical composition, linear and nonlinear optical analyses, thermal, and dielectric characterizations of l-histidine derivatives were conducted. Most of the l-histidine complexes were found to be crystallized in orthorhombic and monoclinic crystal systems with P212121 and P21 space groups. The crystalline perfections of the samples were analyzed by the HR-XRD method. The energy-dispersive X-ray (EDX) spectroscopic technique was applied to evaluate the chemical content of the compounds. FT-IR and FT-Raman techniques were used to recognize the molecular vibrations and functional groups of the l-histidine derivatives. The UV-visible and photoconductivity studies were done to examine the optical behaviors of the developed crystals. Most of the crystals were found to have excellent optical transparency and wide bandgaps. It has been observed that l-histidine hydro-fluoride dehydrate and l-histidine tetrafluoroborate are found to have the highest second harmonic generation (SHG) efficiencies. The dielectric analyses were utilized to study the dielectric constant and dielectric loss variations with the applied frequency. According to the thermal analyses, most of the crystals were found to have substantial thermal stabilities suitable for device applications.

Optimizing dielectric constants for enhanced performance in nanoscale DG-FinFETs: A comprehensive study on short channel effects

This study explores how variations in fin and gate dielectric constants impact nanoscale, DG-FinFETs’ sensitivity to Short Channel Effects (SCEs). Various fin (channel) materials; Gallium Arsenide (GaAs), Gallium Antimonide (GaSb), Gallium Nitride (GaN), and Silicon (Si), are considered. PADRE simulation environment is used to investigate the threshold Voltage (Vth) Roll-off, a crucial performance parameter. GaAs-FinFET, with a gate dielectric and fin dielectric constant values of 15 and 45 shows the lowest threshold voltage of 0.412 V. The study concludes that FinFETs with a higher fin dielectric constant than gate dielectric constant exhibit reduced SCEs, leading to lower power consumption, faster switching, and improved efficiency. This underscores the importance of optimizing dielectric constants, especially the fin dielectric constant, for enhanced DG-FinFET performance.

Linear Capacitive Pressure Sensor with Gradient Architecture through Laser Ablation on MWCNT/Ecoflex Film.

The practical application of flexible pressure sensors, including electronic skins, wearable devices, human-machine interaction, etc., has attracted widespread attention. However, the linear response range of pressure sensors remains an issue. Ecoflex, as a silicone rubber, is a common material for flexible pressure sensors. Herein, we have innovatively designed and fabricated a pressure sensor with a gradient micro-cone architecture generated by CO2 laser ablation of MWCNT/Ecoflex dielectric layer film. In cooperation with the gradient micro-cone architecture and a dielectric layer of MWCNT/Ecoflex with a variable high dielectric constant under pressure, the pressure sensor exhibits linearity (R2 = 0.990) within the pressure range of 0-60 kPa, boasting a sensitivity of 0.75 kPa-1. Secondly, the sensor exhibits a rapid response time of 95 ms, a recovery time of 129 ms, hysteresis of 6.6%, and stability over 500 cycles. Moreover, the sensor effectively exhibited comprehensive detection of physiological signals, airflow detection, and Morse code communication, thereby demonstrating the potential for various applications.

Change of Dielectric Constant of Highly Doped-Silica Glass Used in Optical Fibers with Frequency and Temperature Under the Effect of Polarization

In this study, the variation of the dielectric constant, i.e. relative permittivity of highly doped-silica glass used in optical fibers with frequency and temperature under the effect of polarization has been investigated. In this context, simulations of the relationship between the dielectric constant and both frequency and temperature have been carried out in the Matlab environment. According to simulation and theoretical analysis, it has been concluded that the dielectric constant of highly doped-silica glass tends to increase with the increase of ambient temperature. On the other hand, as the frequency of the source increases linearly, the dielectric constant decreases. Hence, the variations of highly doped-silica glass with temperature and frequency have been found to be 2.884 × 10-5 (°K)-1 and – 7.50 × 10-15 (Hz)-1, respectively. Moreover, in response to the change in frequency between 1011 Hz and 1012 Hz, the dielectric constant has taken values between 2.085 and 2.070. Additionally, for dielectric constant variations in 2.070 – 2.085 range, values of the relative change in polarization have been obtained in the range of 9.4695 × 10-12 F/m – 9.6023 × 10-12 F/m.

Dynamic cerebral blood flow assessment based on electromagnetic coupling sensing and image feature analysis.

Dynamic assessment of cerebral blood flow (CBF) is crucial for guiding personalized management and treatment strategies, and improving the prognosis of stroke. However, a safe, reliable, and effective method for dynamic CBF evaluation is currently lacking in clinical practice. In this study, we developed a CBF monitoring system utilizing electromagnetic coupling sensing (ECS). This system detects variations in brain conductivity and dielectric constant by identifying the resonant frequency (RF) in an equivalent circuit containing both magnetic induction and electrical coupling. We evaluated the performance of the system using a self-made physical model of blood vessel pulsation to test pulsatile CBF. Additionally, we recruited 29 healthy volunteers to monitor cerebral oxygen (CO), cerebral blood flow velocity (CBFV) data and RF data before and after caffeine consumption. We analyzed RF and CBFV trends during immediate responses to abnormal intracranial blood supply, induced by changes in vascular stiffness, and compared them with CO data. Furthermore, we explored a method of dynamically assessing the overall level of CBF by leveraging image feature analysis. Experimental testing substantiates that this system provides a detection range and depth enhanced by three to four times compared to conventional electromagnetic detection techniques, thereby comprehensively covering the principal intracranial blood supply areas. And the system effectively captures CBF responses under different intravascular pressure stimulations. In healthy volunteers, as cerebral vascular stiffness increases and CO decreases due to caffeine intake, the RF pulsation amplitude diminishes progressively. Upon extraction and selection of image features, widely used machine learning algorithms exhibit commendable performance in classifying overall CBF levels. These results highlight that our proposed methodology, predicated on ECS and image feature analysis, enables the capture of immediate responses of abnormal intracranial blood supply triggered by alterations in vascular stiffness. Moreover, it provides an accurate diagnosis of the overall CBF level under varying physiological conditions.

Tunable Dielectric Spectroscopy of PVDF Thin Films Crossbred with TiO2 Nanoparticles for the Storage Devices

AbstractPolyvinylidenefluoride (PVDF) is a semi‐crystalline ferroelectric polymer with a wide range of interesting properties and shows potentiality in a variety of technological applications. Flexible thin films of PVDF nanocomposites (NCs) have attracted many researchers due to their tunable electronic properties. This paper reports the synthesis, characterization, and dielectric studies of PVDF‐TiO2 NC thin films. The synthesized films are self‐supporting thin and the average thickness of the thin films is 60 µm measured using a Digital thickness gauge of resolution 0.01 mm. TiO2 nanoparticles are prepared using the combustion method. Commercially available PVDF granules are used to develop PVDF‐TiO2 NC thin films using the film casting technique. The structural study of the prepared thin films is carried out using XRD that confirms the retention of the β‐phase of PVDF. The functional group and bonding nature have been studied using FTIR Spectroscopy. The thermal stability of the NC thin films is studied using TGA. The variation of dielectric constant (DC), dielectric loss (DL), AC conductivity, and dissipation factor of the medium of pristine PVDF and PVDF‐TiO2 NC thin films are studied in the frequency range of 10 Hz to 8 MHz at ambient temperature. The dielectric constant of PVDF‐TiO2 NC thin films increases up to 8 wt% and anomaly for 10 wt% of TiO2 fillers in the PVDF matrix at a lower frequency and found to decrease with increasing frequency. The dielectric loss of NC thin films is high at a lower frequency and decreases with an increase in the frequency that is in good agreement with the Maxwell–Wagner type of interfacial polarization. At lower frequencies, the dielectric constant of PVDF‐TiO2 NC increases with the increase in filler content. AC conductivity shows a sharp increase at higher frequencies whereas the dissipation factor of the polymer NCs remains unaltered with respect to frequency by maintaining the trend. This suggests that PVDF‐TiO2 NC is potential material for energy storage devices.

A novel methodology for designing Mono/Bi-slab X-band microwave absorbers of Carbon-Powder composites

This work introduces a methodology for the design of X-band microwave absorbers using carbon-graphite powder composites. The reflection loss (RL) is adjusted through variations in sample thickness, mono/bi-slab geometries, and effective dielectric constant. The impact of the particle size of the powders and the volume fraction (v.f.) of the composites on the effective dielectric permittivity has been systematically investigated. The Nicolson-Ross-Weir (NRW) conversion and the Birchak dielectric mixing model were employed. Optimal absorption conditions predicted by RL simulations were validated through experimental waveguide measurements for mono/bi-slab systems of paraffin-carbon composite samples. The mono-slabs with a particle size of 3.5 μm showed the best versatility for tailoring the RL in the X-band through v.f. variations while maintaining a fixed thickness of 2 mm. In addition, a bi-slab system (powder-paraffin/paraffin) for such powder size, at 18.0 % of v.f., showed an enhanced RL with a bandwidth of 2.6 GHz and a minimum of − 40 dB (at 11 GHz). Other dielectrics based on resin:paint mixtures were tested to replace the paraffin-matrix, revealing a strong powder-matrix interaction capable of modulating the effective dielectric permittivity. Finally, experimental antenna RL measurements conducted in free space were corroborated by theoretical simulations based on the waveguide characterizations.

High quality factor double negative metamaterial for textile fabric and fabric moisture sensing applications

This study introduces an innovative high-Quality factor (Q-factor) double negative (DNG) metamaterial sensor designed for textile fabric and fabric moisture sensing applications in the dynamic realm of textile innovation. The sensor is specifically designed to detect the dielectric properties and moisture content of different textile fabrics. The high Q-factor of this metamaterial structure ensures heightened sensitivity and accuracy in fabric sensing, facilitating precise detection of even subtle changes in fabric properties. By measuring frequency shifting and analyzing S21 values, the sensor provides crucial information about the fabric’s dielectric characteristics. Sensing experiments conducted on various fabrics, including cotton, denim, corduroy, organza, and polyester unveil distinctive patterns of frequency shifting and Q-factors, establishing a nuanced link between fabric structure and sensor performance. The proposed sensor is capable of detecting fabrics with a very low dielectric constant variation of 0.05. In the experiment, the high-dielectric fabric denim (1.7) exhibited frequency shifting and Q-factor of 6970 and 834.87, respectively. Moreover, it is worth noting that the low-dielectric fabric organza (1.03) exhibits frequency shifting and Q factors of 2190 and 1367.03, respectively. Experimental results affirm the prominent efficacy of the proposed sensor in fabric and fabric moisture sensing. Its high Q-factor empowers the sensor to accurately detect and monitor fabric properties, rendering it highly suitable for critical tasks such as quality control, energy efficiency optimization, and process enhancement within the textile industry. The proposed metamaterial sensor (MMS) can significantly contribute to the development of a smart textile sensing technology and pave the way for innovative applications in the textile industry.

Boosting Photovoltaic Output by Dual External Manipulations on 1D Ferroelectric Nanorods Solar Cell: Electric Field and Giant Dielectric Constant Variation

Unlike common photovoltaic (PV) cells whose performance has been anchored, the merits for the cells made of ferroelectric crystals, due to the non‐centrosymmetric structure, provide possibility to further enhance the efficiency by dual external manipulations through increasing the internal electric field strength and the dielectric screening effect, based on anomalous photovoltaic (APV) arisen by the external poling and giant dielectric constant variation through temperature‐controlled ferro‐paraelectric phase transition. In this study, a synergistic effect achieving a 67% improvement in power conversion efficiency (PCE) of the n‐i‐p configuration solar cell by ferroelectric polarization and high dielectricity is observed, taking c‐axis‐aligned single‐crystalline ferroelectric SbSI nanorods as the active layer. The opposite poling effects are revealed leading to asymmetric characteristics in the n‐i‐p configuration. The enhancements of Jsc induced by inherent giant variation imply strong dielectric screening facilities to lower carrier cross section captured by charged defects, uniformly suppressing various recombination mechanisms, understood by the Langevin model. Therefore, solar cells employing n‐i‐p structured ferroelectric thin films as absorbing layers hold promising potential for achieving defect‐tolerance high performance through rational design, external polarization, and dielectric property control.

(Invited) Comparison of Empirical Models for Broadband Insertion Losses in TSV-Interconnects

The reliability of through silicon via (TSV)-interconnects depends on various factors including integration schemes, manufacturing process (construction materials, wafer-scale homogeneity, thermal budget) and operating conditions. The magnitude of the frequency-dependent $S_{21}$ microwave scattering parameter quantifies insertion losses in TSV-interconnects. The insertion loss depends on the instantaneous electrical characteristics of the device under test. We attribute insertion loss (which affects device reliability) to reorientation of electrically active defects, cracks, voids, dielectric constant variation, and water molecules affected by heat. We model insertion losses with equivalent circuit models of varying complexity. We compare results determined with global and local models fit to low-frequency and high-frequency subsets of the full spectrum. We estimate model parameters with a stochastic optimization implementation of the Levenberg-Marquadt method. To illustrate the relevance of this methodology, for TSV-interconnects from two different providers, we quantify how estimated model parameters vary with thermal cycles for TSV-interconnects fabricated at particular wafer locations.

Calculating Dielectric Constant at the Interface Between Polyethylene and Copper Using Microscopic Polarization Theory

The relative dielectric constant is the main electric property of polyethylene (PE) as a dielectric material. Based on experimental findings, the dielectric constant of bulk PE has been known to be constant. However, when interfaced with copper –as it is the case in most power applications- the dielectric constant may differ from that value at interface region in atomic scale, which in turn affects the charge injection process. This is further complicated by the inevitable presence of chemical impurities at the interface, where the dielectric constant becomes position-dependent and depends on the type of impurity. In this work, the dielectric constant is calculated for the cases of a pure slab of PE during the interface between PE and copper, and finally with chemical impurities present in the interface region. In those cases, the microscopic polarization theory is used in calculating the position-dependent relative dielectric constant. This theory makes use of the charge density distribution under an applied electric field, which is computed using the density functional theory (DFT). It is found that the calculated dielectric constant varies at the interface region within a range of a few Angstroms, beyond which it becomes constant well within the bulk polyethylene. The dielectric constant variation at the interface region is then used to study the impact on the injection process using the Schottky injection mechanism. The injection current density is computed from Schottky injection law as a function of applied field at different dielectric constant values. It is found that the injection current increased with decreasing the dielectric constant at the interface region. The paper concludes that the relative dielectric constant varies at the interface due to the morphological deformation between the polyethylene chains and the copper atoms. This variation is further enhanced in the presence of chemical impurities. It is further concluded that the injection current density does not only depend on the barrier height, but also on the varying relative dielectric constant.

Impact of pH levels on the morphological, dielectric and impedance spectral behaviour of cobalt oxide nanomaterials

Pure Co3O4 nanomaterials were synthesized by using Sol-Gel technique at various pH levels (7, 8 and 9). Morphological and structural analysis was done by X-ray diffraction method (XRD), scanning electron microscope (SEM) and energy-dispersive spectroscopy EDX. The X-ray diffraction patterns revealed that the prepared samples crystallized in a cubic structure without any impurities. SEM micrographs validated the influence of pH in altering the morphology of the synthesized compound. The elemental spectrum analysis EDX confirms the presence of cobalt and oxygen without any impurities. Variation of dielectric constant, dielectric loss and impedance were analyzed for various temperatures and different pH values. Dielectric loss value increases at high temperature due to the thermal disturbance of the atoms. Cole-Cole impedance plot gives the information about grain and grain boundaries. DC electrical conductivity values of Co3O4 nanomaterials in the temperature range 40ºC to 250ºC increases with increase in pH level from 7 to 9. Arrhenius plot of Co3O4 nanoparticles confirmed that the activation energy at various temperature increases with increase in pH levels upto 8, then decreases for pH level 9.

Synthesis, structural, impedance, optical, Mössbauer characterizations and magnetic studies of Pb-containing germanate compounds

The orthorhombic antiferromagnetic germanate minerals Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9 have been prepared via solid state reaction procedure. An extensive study of structural, dielectric, optical and magnetic properties of both the germanates have been investigated by employing different measurements such as X-ray diffraction, FTIR, SEM, impedance, UV–Vis–NIR & Mössbauer spectroscopic and magnetometary. Rietveld refinement of room temperature XRD patterns revealed that both the compounds crystallize in the orthorhombic space group Pbcn. FTIR spectrum exhibits the presence of M−O & Ge–O bonds which confirms strong chemical bonding. Morphological analysis through SEM showed good crystallinity of both the samples. The variation of dielectric constant, loss tangent and impedance with frequency have been studied and it has been established that both the germanates are semiconducting at 300K (RT) which may be attributed to the stacking of ions at grain boundaries. The optical band gaps estimated by UV–Vis–NIR spectroscopic measurements further confirms the semiconducting nature of the prepared germanates. 57Fe Mössbauer spectroscopic measurement on synthesized Pb2Fe2Ge2O9 sample was carried out at RT. The obtained values of IS and QS showed that iron is in Fe3+ high spin state (t2g3eg2,s=5/2) and occupy two different sites, Fe1 and Fe2. The field dependent magnetization measurements show that both the compounds display dominant paramagnetic nature at 300K. The temperature dependent magnetization data reveal very sharp first order type AFM to PM transition at TN ∼50K and TN ∼8K for Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9, respectively, and weak FM nature below Neel temperature. The field dependent properties of both the compounds have been analyzed by drawing the M versus H plots at low and room temperatures. The values of calculated effective magnetic moment 6.07μB and 3.95μB for Fe3+ and Mn3+ ions are in the high spin states (t2g3eg2,s=5/2 and )t2g3eg1,s=2.

Structural, magnetic, dielectric, magneto-electric and ferroelectric properties of BaTiO3- NiFe2O4 multiferroics

Multiferroics having composition yNiFe2O4 - (1-y) BaTiO3(y = 0.10, 0.30 and 0.50) have been prepared through the solid-state reaction route. These samples constitute NiFe2O4 as the ferromagnetic phase and BaTiO3as the ferroelectric phase. The X-ray diffraction (XRD) has been carried out to investigate the crystal structure formation and phase purity of the prepared ceramic samples. Rietveld refinement of XRD patterns confirm the presence of cubic (Fd3m) and tetragonal (P4mm) symmetries in all the samples. The effect of ferrite (NFO) concentration on magnetic, dielectric, ME coefficient and ferroelectric properties of samples has been studied further. The recorded M-H loops at room temperature, reflects the ferromagnetic nature of all samples. These hysteresis loops are fitted by LAS (law of approach to saturation), and the values of various magnetic parameters are evaluated. A gradual enhancement in magnetic parameters is noticed with an increased in NFO concentration. Variations of dielectric constant (ɛ') and loss tangent (tan δ) as a function of frequency as well as of temperature at various selected frequencies (10 kHz, 100 kHz, 500 kHz, and 1 MHz) have been studied. The highest value of magnetoelectric (ME) response has been observed for thesample0.10NiFe2O4-0.90BaTiO3. P-E loops show an enhancement in both the coercive field and the remnant polarization with an increment in ferrite content at room temperature.

High dielectric Al2O3-(20–30 wt%) HDPE composites processed via cold sintering

In the present work, the dielectric properties of cold sintered alumina (Al2O3) reinforced with 20–30 wt% HDPE composite was investigated. The Al2O3-HDPE composites were successfully processed via cold sintering at extremely low temperature in the range of 80–120 °C for 120 min with the application of uniaxial pressure of 500 MPa under vacuum. In fact, cold sintering is a promising method to consolidate ceramic-polymer composites with very large difference in melting points and other thermo-physical/chemical properties. In the present work, high dielectric constant (ε’) of 11.73 and low dielectric loss (tanδ) of 0.0076 measured for Cold Sintering Processed (CSPed) Al2O3-20HDPE and a little low ε’ of 9.13 and low tanδ of 0.0066 was evident for CSPed-Al2O3-30HDPE at 1 MHz. Such differences in the dielectric properties of the Al2O3-20,30 HDPE composites depend on the crystallite size, dangling bond density and microstrain of the materials. Increase in ε’ with temperature is noticed for CSPed-A20H. Moreover, for CSPed-A20H at 1 MHz the temperature variation of dielectric constant (TCC) of 186.94 ppm/°C (or 0.018694 %/°C) was estimated and it reflects a marginal variation of ε’ with temperature. The coefficient of thermal expansion (CTE) of 87.25 × 10−6 °C−1 and 109.3 × 10−6 °C−1 was estimated for CSPed-A20H and CSPed-A30H, respectively. Overall, the cold sintered Al2O3-20HDPE composites exhibited comparable or better dielectric properties than Al2O3 based materials (as reported in the literature) processed by conventional sintering or cold sintering processes.

Dielectric, AC conductivity, and complex impedance spectroscopy studies of Ti2CTx MXene reinforced polyvinyl alcohol nanocomposites

AbstractHerein, Ti2CTx MXene‐Polyvinyl alcohol (PVA)  nanocomposite films with different weight percent (wt%) of MXene loadings were successfully prepared using the facile solution casting method. The structural, morphological, optical, thermal, and tensile properties of the nanocomposite films were analyzed using FTIR, XRD, Raman, SEM, UV–Vis spectroscopy, TG‐DTA, mechanical tests, and so forth. The variation in dielectric constant, loss tangent, and AC conductivity of the nanocomposite films was analyzed in the range of 1 Hz to 10 MHz with the variation of temperature (30–150°C) and MXene concentrations (5–20 wt%) using impedance spectroscopy. The nanocomposite films showed a very high dielectric constant in the range of ~105 for lower frequency and very low dielectric loss in the range of 0–1 for higher frequency (100 kHz–10 MHz). The dielectric constant, loss tangent, and AC conductivity values increased at a certain temperature and further decreased with increase in temperature. The increase in filler concentration increased the values of these investigated electrical parameters but at a concentration of 20 wt%, the nanocomposite films reached the percolation limit, and hence a slight reduction in the dielectric properties was noticed. Moreover, the complex impedance spectroscopy studies of the nanocomposite films were also carried out and their corresponding circuit diagrams were fitted according to the obtained cole‐cole plots.

Effect of morphology and particle size on the electrical properties of nano-nickel ferrite

Four powder samples of Nickel ferrite (NiFe2O4) with different morphology and nanoparticle size have been synthesized by various methods: electrospinning, hydrothermal, green, and sol-gel. Through the use of XRD, FT-IR, SEM, TEM, and BET techniques, the prepared powders were characterized. The produced ferrite displayed a cubic spinel phase with various nanofiber, nanotube, nanorod, and nanosphere morphological structures. The electrical conductivity values for each sample increased with increasing temperature indicating the semiconducting behavior of all samples. The conductivity values were found to be dependent on each nanoparticle's size and morphology. The variation of dielectric constant (ε′), dielectric loss (ε′′), and ac conductivity for the investigated samples at different temperatures and frequencies has been studied. Both dielectric constant (ε′) and dielectric loss (ε′′) were decreased with the increase of frequency while A.C. conductivity increased. Knop's phenomenological theory explains the frequency variation of (ε′ and ε′′). The hopping of electrons and holes is suggested to be the electrical conduction mechanism.

Improper High-Tc Perovskite Ferroelectric with Dielectric Bistability Enables Broadband Ultraviolet-to-Infrared Photopyroelectric Effects.

The photopyroelectric effect in ferroelectrics has shown great potential for application in infrared detection and imaging. One particular subclass is broadband with dielectric bistability, which allows for large pyroelectric figures-of-merit (FOMs). Herein, an improper high-Tc perovskite ferroelectric, (IA)2 (EA)2 Pb3 Cl10 (1, where IA is isoamylammonium and EA is ethylammonium) is presented, in which spontaneous polarization (Ps ) stems from the dynamic ordering of organic cations and the tilting of distorted PbCl6 octahedra. Notably, 1 displays unusual dielectric bistability with small variations in the temperature-dependent dielectric constants near Tc =392 K; this bistable attribute endows large pyroelectric FOMs with peak voltage efficiency (FV =1.7×10-2 cm2 µC-1 ) and sensitivity (FD =3.9×10-4 Pa-1/2 ). These FV and FD parameters, beyond those of their proper counterparts, make 1 a promising candidate for infrared photodetection. As expected, the broadband photopyroelectric effects observed in 1 covered the ultraviolet to infrared-II spectral region (266-1950nm). Such Ps -directed photoactivities overcome the optical bandgap limitation and allow for wide-wave photodetection. As an innovative study on improper ferroelectricity, light is shaded here on the targeted engineering of new electrically ordered candidate materials for smart optoelectronic devices.

Influences of substituting of (Ni1/3Nb2/3)4+for Ti4+on the phase compositions, microstructures, and dielectric properties of Li2Zn[Ti1−x(Ni1/3Nb2/3)x]3O8(0 ≤x≤ 0.3) microwave ceramics

Complex ions substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics. In this work, Li₂Zn[Ti_1-<em>x</em>(Ni_1/3Nb_2/3)<em>_x</em>]₃O₈ (LZTNN<em>x</em>, 0 ≤ <em>x</em> ≤ 0.3) ceramics were designed based on complex ions substitution strategy, following the substitution rule of radius and valence to investigate the relationships between phase composition (containing oxygen vacancies and Ti³⁺ ions), microstructure, and microwave dielectric characteristics of LZTNN<em>x</em> ceramics. The samples maintained a single Li₂ZnTi₃O₈ solid solution phase as <em>x</em> ≤ 0.2 whereas the <em>x</em> = 0.3 sample produced a secondary phase with LiNbO₃ structure. The appropriate amount of (Ni_1/3Nb_2/3)⁴⁺ substitution could slightly improve the densification of LZTNN<em>x</em> ceramics due to the formation of Li₂ZnTi₃O₈ solid solution accompanied by a decrease in average grain size. The presence of a new <em>A</em>_1g Raman active band at about 848 cm^-1 indicated that the local symmetry changed, affecting the atomic interactions of LZTNN<em>x</em> ceramics. The variation in dielectric constant (ε<em>_r</em>) was closely related to molar volume ionic polarizability, and the temperature coefficient of resonant frequency (τ<em>_f</em>) was related to the bond valence of Ti. The increase in density, the absences of Ti³⁺ ions and oxygen vacancies, and the reduction in damping behavior were responsible for decreased dielectric loss. The LZTNN0.2 ceramic sintered at 1120 ^oC exhibited favorable microwave dielectric properties: ε<em>_r</em> = 22.13, quality factor (<em>Q</em>×<em>f)</em> = 97350 GHz, and τ<em>_f</em> = −18.6 ppm/^oC, which might be a promising candidate for wireless communication applications in highly selective electronics.