Broadband Dielectric Spectrometer Research Articles

Electrical, optical, and electrochemical performances of phosphate-glasses-doped with ZnO and CuO and their composite with polyaniline

Phosphate-based glasses (PBG) with appropriate doping agents have been used as solid electrolytes in solid-state ionic devices. Therefore, more light was shed on the electrical, optical, and electrochemical behavior of the phosphate-based glasses (PBG), containing ZnO or CuO in the absence and existence of conductive polyaniline (PANI), since no publications are available concerning this work. The glass samples were prepared by the rapid quenching method, then mixing phosphate glass and polyaniline (PANI) with metal oxide (ZnO, CuO). They were characterized by different techniques; diffuse reflectance spectrophotometer (DRS), broadband dielectric spectrometer (BDS), cyclic voltammetry (CV), and charge–discharge techniques. In the DRS study, the direct and indirect band gap were calculated from Tauc’s relationship where CuO-doped glasses have higher values than ZnO-doped glasses. In the BDS study, the permittivity of all glass compositions decreased while AC conductivity increased with increasing frequency. AC conductivity of PBG doped with metal oxides and mixed with PANI exhibited semiconducting features (6.8 × 10–4 S/cm). Further, these composites exhibited lower loss tangent (0.11), and giant permittivity (186,000) compared to the pure PBG. Also, the electrochemical study exhibited that the composite with 7% CuO content has the highest specific capacitance value (82.3 F/g at 1.0 A/g) which increased to about 113% of its first cycle and then decreased to about 55% after 2500 cycles and finally increased again to 77% after 4500 cycles, indicating its good stability. The combination of optical, electrical, and electrochemical features of these composites suggests their use for energy generation and storage devices.

Effect of Europium Addition on the Microstructure and Dielectric Properties of CCTO Ceramic Prepared Using Conventional and Microwave Sintering.

In this work, Eu2O3-doped (CaCu3Ti4O12)x of low dielectric loss have been fabricated using both conventional (CS) and microwave sintering (MWS), where x = Eu2O3 = 0.1, 0.2, and 0.3, respectively. According to X-ray diffraction (XRD) and scanning electron microscope (SEM) reports, increasing the concentration of Eu3+ in the CCTO lattice causes the grain size of the MWS samples to increase and vice versa for CS. The X-ray photoelectron spectroscopy (XPS) delineated the binding energies and charge states of the Cu2+/Cu+ and Ti4+/Ti3+ transition ions. Energy dispersive spectroscopy (EDS) analysis revealed no Cu-rich phase along the grain boundaries that directly impacts the dielectric properties. The dielectric characteristics, which include dielectric constant (ε) and the loss (tan δ), were examined using broadband dielectric spectrometer (BDS) from 10 to 107 Hz at ambient temperature. The dielectric constant was >104 and >102 for CS and MWS samples at x > 0.1, respectively, with the low loss being constant even at high frequencies due to the effective suppression of tan δ by Eu3+. This ceramic of low dielectric loss has potential for commercial applications at comparatively high frequencies.

Synthesis, structural, micro structural, optical, magnetic and dielectric properties of Nd doped multiferroic Bismuth iron oxide

Neodymium doped Bismuth Iron Oxide (NdBiFeO3 - NBFO) with the composition Bi1-xNdxFeO3 (x = 0.02, 0.04&0.06) has been synthesized by microwave assisted combustion method. The properties of Neodymium (Nd3+) doped BFO nanoparticles were studied using various analytical techniques. The X-ray diffraction revealed the Rhombohedra phase formation of doped samples and decrease in crystallites size with increase in dopant concentration. The Fourier transform infrared spectroscopy confirms the presence of molecular vibration. Optical properties were studied using the UV data and optical band gaps of NBFO were calculated. The direct band gap of the materials is found to be 1.02eV, 1.78eV and 1.89eV for. The magnetic properties are studied using M-H graphs obtained from the Vibrational Sample Magnetometer. The M-H hysteresis loop shows decreased saturation magnetization (MS) and coercivity (HC) but increased remnant magnetization (M r) on substitution. The dielectric properties of doped samples were investigated using broad band dielectric spectrometer in the frequency range of 10 Hz to 10 MHz at room temperature.

Effect of clay/nepheline tailing ratio on the dielectric relaxation and conduction mechanism of the conventional ceramic

The dielectric relaxation and conduction mechanism of 40 wt% nepheline tailing and 60 wt% clay-based ceramic, i.e., the 40/60 ceramic, have been investigated over wide ranges of frequency and temperature, using a broadband dielectric spectrometer (BDS) and then compared with the data recently reported for the 50/50 ceramic. Both 40/60 and 50/50 ceramics were fabricated by grinding the raw materials to be very fine, wet homogenously mixing, drying and finally firing at 1200 °C. Their crystalline phases identified by X-ray diffraction were quartz, hematite, cristobalite, and albite. The 40/60 ceramic of lower glassy phase (nepheline tailing) content displays lower crystallinity than the 50/50 ceramic. Its conduction activation energies (Eac) show values between 0.12 and 0.32 eV, corresponding to the activation energy of oxygen vacancies (Vo++ ~ 0.22 eV). As oxygen vacancies migrate at relatively low operating voltages, the fabricated ceramics would be promising in manufacturing the random access memory (RAM), taking into consideration that the 50/50 ceramic is more useful than the 40/60 ceramic. As a result, nepheline tailing or the glassy phase component may generate more oxygen vacancies and thus enhance the ceramic electrical properties. Finally, the conduction mechanism of both ceramics is described via the correlated barrier hopping (CBH) model.

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Thermistor with Variable Rate of Negative Temperature Coefficient of Resistance Made from Egyptian Raw Materials

A dual-function negative temperature coefficient thermistor (NTCR/AB) has been successfully fabricated from the available and inexpensive Egyptian raw materials (clay and nepheline tailings). The disc-shaped thermistor was fabricated by grinding and mixing its raw material in a porcelain ball mill for 1 h, drying at 110°C for 1 h, pressing under 30 kN, drying at 110°C for 24 h, firing at 550°C, and finally sintering at 1200°C for 1 h. The crystalline phases developed in the ceramic thermistor were characterized by x-ray diffraction. The thermistor performance has been examined by measuring its electrical resistivity (ρ) over a wide range of temperature (− 100°C to + 200°C) at a constant frequency (0.1 Hz), using a broadband dielectric spectrometer. The fabricated ceramic thermistor showed a decrease in resistivity with increasing temperature at two different rates, displaying the NTCR/AB. One of its functions (NTCR/B) works in a wide temperature range (− 20°C to 200°C) and shows high thermistor constant values (3009–4638 K), while its second function (NTCR/A) works in a narrower temperature range (− 40°C to − 20°C) and shows exceptionally high thermistor constant values (40,122 K). NTCR/B can be used for many electronic devices applications, while NTCR/A is promising for thermal switching devices.

Mechanical and dielectric properties at liquid nitrogen temperature of epoxy/AlN composites modified with different contents of flexible amine

Epoxy resin has been wide applied in aerospace, superconducting industries because of the high electrical insulation, excellent adhesive properties and great chemical resistance. In this paper, epoxy/AlN composites were prepared by changing the content of the flexible amine (D-230) and the diethyl toluene diamine (DETDA) from 0 to 100 wt%. The effects of different ratios of D-230 and DETDA were investigated on the mechanical and dielectric properties of epoxy/AlN composites at liquid nitrogen temperature (77 K) and room temperature (RT). The properties of the samples were characterized by flourier transformed infrared (FTIR), scanning electron microscopy and broadband dielectric spectrometer. FTIR results showed that AlN particles were successfully modified by the silane coupling agent (KH-560). Tensile testing showed that the addition of flexible diamines generally improved the elongation at break at both RT and 77 K and the tensile strength at 77 K. The introduction of D-230 led to a lower dielectric constant at cryogenic temperature than that at RT.

Structural, Magnetic, and Dielectric properties of Sr4Fe6O13 ferrite prepared of small crystallites

A stable Sr4Fe6O13 was prepared as small crystallites by auto-combustion of a sol-gel in air followed by annealing the later at pertinent temperatures. A green sample, as annealed at elevated temperatures, yields a single Sr4Fe6O13 phase of tailored magnetic properties. The structural, morphological, magnetic and electrical properties were investigated by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer, and broadband dielectric spectrometer. Hard magnetic Sr4Fe6O13 properties arise with saturation magnetization Ms = 12.4 emu/g, coercivity Hc = 3956.7 Oe and squareness 0.512. Studies made at low temperatures reveals Ms decreasing on increasing temperature from 17.5 emu/g at 85 K down to 12.4 emu/g at 305 K, while Hc rises from 1483 Oe at 85 K to 1944 Oe at 305 K. The ac-conductivity follows the Jonscher relation. The dc-conductivity at high temperatures/low frequencies exhibits a plateau and it depends linearly on a characteristic frequency according to the Barton-Nakajima-Namikawa) relation.

In situ synthesis of Fe3O4@ cyanoethyl cellulose composite as antimicrobial and semiconducting film

Cyanoethyl cellulose (CEC)/ magnetite (Fe3O4) flexible composite film with enhanced dielectric and magnetic properties was successfully prepared. CEC has been synthesized from micro crystalline cellulose (MCC). The effects of magnetite mass fraction on the morphology, microstructure, thermal stability, and antimicrobial activity of the as-prepared composite films were investigated. The Vibrating sample magnetometer (VSM) and broadband dielectric spectrometer was also employed to study the magnetic and dielectric properties, respectively. In addition to study the computational calculation of MCC, and CEC by DFT/ B3LYP/6-31G (d) basis sets. The results showed that, the sample that is magnetite free has a diamagnetic response to the applied magnetic field, however the other samples that is loaded with magnetite show super-paramagnetic behavior indicating that the particles’ sizes of the magnetite mostly below 20 nm. Also, antimicrobial activities of composite films against (G + ve), (G-ve), were investigated.

Dielectric Relaxation Processes in Mn2O3/Reduced Graphene Oxide Nanocomposites

One essential for developing electronic materials for device applications is an understanding of the materials’ dynamic relaxation processes. This paper seeks to improve our understanding of the relaxation processes in pure Mn2O3 and Mn2O3/reduced graphene oxide (RGO) nanocomposites on the basis of the capacitive contributions of grain and grain boundaries (GBs). To achieve this, the dielectric properties for pure Mn2O3 and Mn2O3/xRGO (x = 5, 10 and 20 wt.%) nanocomposites, prepared theby sol–gel method, were investigated over a wide frequency range at room temperature using a broadband dielectric spectrometer (BDS). Crystalline structure, molecular structure and microstructure of samples were characterized by x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope, respectively. XRD analysis showed the formation of orthorhombic crystalline structure in all samples with no considerable changes in the crystalline structure. FTIR spectra did not show new absorption bands upon introducing the graphene content. Characteristic peaks corresponding to Mn-O vibration were found to have shifted to lower wavenumbers, indicating an increase of particle size. The dielectric study showed some changes in the dielectric properties of the Mn2O3/RGO nanocomposites. For pure Mn2O3, two relaxation processes were clearly observed; the slower one positioned at high relaxation time (τ = 1.7 × 10−2 s) is associated to the GBs capacitive contribution, while the faster one of lower τ (= 2.5 × 10−5 s) is associated to the grain capacitive contribution. For Mn2O3/RGO nanocomposites, τ for both process slightly increased with increasing RGO up to 10 wt.% then remarkably decreased to much lower values at 20 wt.%. Interestingly, BDS, rather than XRD and FTIR techniques, is considered as a powerful and sensitive technique, even for small changes in Mn2O3/RGO nanocomposites.

Sintering and dielectric behavior for doped cordierite by xCuO within MgO (1-x)–Al2O3–SiO2 ceramics

Crystalline structure, morphology, quantitative chemical constitution and dielectric properties of pure cordierite ceramic (CC) bodies and these doped with xCuO in formula MgO(1-x)Al2O3SiO2 (x = 0, 0.02, 0.04 and 0.06 wt%), prepared by a conventional solid state ceramic process, were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF) and broadband dielectric spectrometer (BDS), respectively. Experimental results showed that doping with CuO results in lowering sintering temperature, lowering porosity, increasing bulk density and formation of copper magnesium silicate (CuMgSi2O) phase. CuMgSi2O which was formed with the highest content of CuO (0.06 wt %) increases the glassy phase, i.e. crystalline phase decreases of CC. Accordingly, the dielectric properties of CC found to be affected by CuO content. For instance, the permittivity and loss tangent slightly increased upon doping with 0.02 wt % CuO and then considerably decreased for sample doped with 0.06 wt % CuO due to formation of CuMgSi2O phase. Particularly, the loss tangent attained much lower values (0.003 at 25 °C) upon doping with 0.06 wt% CuO. Interestingly, such materials of very low loss can be used as candidates for wireless communication systems as well as in several electronic devices.

Frequency and Voltage Dependence of the Dielectric Properties of Ni/SiO2/P-Si (MOS) Structure

The frequency (10 - 107 Hz), temperature (303-363 K) or /and bias voltage (−2 to 2 V) dependence of the dielectric properties of Ni/SiO2/p-Si (MOS), have been investigated using the broadband dielectric spectrometer (BDS). Molecular structure and microstructure have been characterized using X - ray diffraction (XRD) and scanning electron microscope (SEM), respectively. From the experimental results, the capacitance–frequency (C-f) characteristics for MOS structure described as a series capacitance (Cs) in the oxide layer (SiO2) and a depletion layer in the semiconductor (p-Si). Interestingly, the capacitance over the whole frequency range for all temperatures are hardly distinguished particularly in the accumulation region, exploring enhancements of the electrical performance for MOS structure. Value of the flat band voltage (VFB) separating the accumulation and depletion regions was determinate at −0.5 V. Furthermore, thickness of the interfacial layer (SiO2) found to be ~580 A. Both C and e' found to be strongly temperature and frequency dependent particularly at high temperatures and low frequencies due to creation of an inhomogeneous layer at the SiO2/p-Si interface, exploring Maxwell-Wagner or interfacial polarization. Variation of e' and e'' with frequency revealed to the existence of surface states or traps (Nss) located at interfacial layer (SiO2), dipole or/and surface polarization. The average conductivity value of MOS structure found to be 1.2 × 10−7 S/cm, exploring semiconducting feature.

Effect of rGO:MWCNTs ratio on electrical conductivity of polyazomethine/rGO:MWCNTs nanocomposites

Using solution blending method, we produced nanocomposites based on polyazomethine (PAZ) loaded with hybrid carbon nanofillers. The nanofillers comprised reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs). The total nanofiller loading was equal to 1 wt% while the rGO:MWCNTs ratio varied as follows: 100:0, 75:25, 50:50, 25:75, and 0:100 wt%: wt%. The complex dielectric permittivity data obtained with a broadband dielectric spectrometer were used to analyze electrical conductivity of the nanocomposites in wide ranges of frequency and temperature. Electrical conductivity was found to increase with increasing MWCNTs portion and its maximum value was achieved when the nanofiller contained the MWCNTs nanoparticles exclusively. We extracted the electrical conductivity components, dc conductivity σdc and ac conductivity σac, and analyzed their behavior as function of frequency and temperature. The temperature dependences of σac were described with the Arrhenius equation, whereas its frequency dependences were characterized with a power function. For explaining the σac behavior, the correlated barrier hopping mechanism was accepted. Interfacial interactions between the hybrid nanofillers and the polymer matrix (the Maxwell-Wagner-Sillars effect) were detected. It was found to be strongly pronounced in the nanocomposites with high portion of MWCNTs in the hybrid fillers.

Study on Detecting Dielectric Properties of Typical Electrical Insulation Materials by Terahertz Wave Spectroscopy

The dielectric properties of the electrical insulation materials is of great importance to the safe operation of the power system. As a promising technique in the field of material testing and with the very adaptive physical modeling of wave transmission process, terahertz wave was used to measure the dielectric properties of five commonly used insulation materials by two methods in this paper. When excluding the echo pulse from the reference signal and the sample signal, a better signal-noise ratio and a wider effective frequency band of spectrums can be obtained. Alternatively, the dielectric properties can also be achieved by separating the main pulse and echo pulse from the sample signal. The latter method makes the sampling of reference signal unnecessary. Furthermore, the dielectric properties of materials were also measured on a relative lower frequency band (1Hz–1MHz) by the broadband dielectric spectrometer. Compared with a relatively lower frequency band, due to the polarization, the dielectric constant of the tested insulation materials was lower on the terahertz band while the dielectric loss tangent was generally higher except the epoxy resin.

Improved dielectric permittivity of NBCTO/epoxy composite films with low dielectric loss

In this paper, NBCTO/epoxy composite films with different contents of NBCTO were prepared by solution mixing and casting method. The structure, morphology, thermostability and dielectric properties of the composite films were studied by X-ray diffraction, scanning electron microscopy, thermo-gravimetric analysis and broadband dielectric spectrometer. The composite film showed a homogeneous structure and better thermostability, and the dielectric permittivity was almost independent of the frequency range from 10 to 106 Hz at room temperature. The dielectric permittivity and dielectric loss of NBCTO/epoxy composite film increased with increasing in NBCTO content, and the dielectric permittivity was as high as 37.10 whereas the dielectric loss was only 0.019 at 1 kHz when the NBCTO volume fraction reached 50 vol%. Theoretical analysis indicated that the dielectric permittivity calculated by the EMT model was close to the experimental data. The results showed that NBCTO/epoxy composite might have potential applications in the electronic devices.

Effects of Moisture, Temperature, and Salt Content on the Dielectric Properties of Pecan Kernels During Microwave and Radio Frequency Drying Processes.

Dielectric properties of materials influence the interaction of electromagnetic fields with and are therefore important in designing effective dielectric heating processes. We investigated the dielectric properties (DPs) of pecan kernels between 10 and 3000 MHz using a Novocontrol broadband dielectric spectrometer in a temperature range of 5–65 °C and a moisture content range of 10–30% wet basis (wb) at three salt levels. The dielectric constant (ε′) and loss factor (ε″) of the pecan kernels decreased significantly with increasing frequency in the radio frequency (RF) band, but gradually in the measured microwave (MW) band. The moisture content and temperature increase greatly contributed to the increase in the ε′ and ε″ of samples, and ε″ increased sharply with increasing salt strength. Quadratic polynomial models were established to simulate DPs as functions of temperature and moisture content at four frequencies (27, 40, 915, and 2450 MHz), with R2 > 0.94. The average penetration depth of pecan kernels in the RF band was greater than that in the MW band (238.17 ± 21.78 cm vs. 15.23 ± 7.36 cm; p < 0.01). Based on the measured DP data, the simulated and experimental temperature-time histories of pecan kernels at five moisture contents were compared within the 5 min RF heating period.

Grain and grain boundaries contributions to dielectric relaxation of the clay-based ceramics

The current paper is a complementary dielectric study on the clay-based ceramics (CBC) to investigate the contribution of grain and grain boundaries to the dielectric relaxations. The dielectric measurements were carried out on the ceramic composed of 50 wt.% clay and 50 wt.% nepheline syenite) over wider ranges of frequency and temperature, using the advanced broadband dielectric spectrometer. Dielectric spectra suggested that the temperature has a significant effect on the electrical microstructure of CBC. They show the existence of two relaxation process associated to the grain boundaries (GBs) and grains in low- and high-temperature regions, respectively. The relaxation process associated with grain is more predominating over GBs relaxation over the temperature range studied. Interestingly, we reported an anomaly feature in dielectric behavior of CBC at − 40 °C at which all dielectric properties changed abruptly.

Thermal responsiveness of hydrogen bonding and dielectric property of polybenzoxazines with different Mannich bridge structures

Variation of hydrogen bonding (HB) and dielectric properties of polybenzoxazines with different Mannich bridge structures at different temperatures are investigated by in-situ Fourier Transform Infrared (FTIR) Spectrometry, perturbation-correlation moving-window two-dimensional (PCMW2D) infrared spectroscopy and Broad Band Dielectric Spectrometer (BDS), respectively. It is found that in phenolic Mannich polybenzoxazine, –OH•••O HB tends to rearrange into thermally stable –OH•••N HB. In arylamine Mannich polybenzoxazine, –OH•••O HB is favorable at relatively low temperature and will dissociate at higher temperature. The PCMW2D infrared spectroscopy reveals that the massive dissociation temperature of –OH•••O HB occurs is generally higher than 100 °C and varies with different polybenzoxazines. The results from BDS suggest that the thermal responsiveness of dielectric properties is closely related to the HB and the thermal resistance of polybenzoxazines. The six-membered –OH•••N HB is beneficial for high frequency stability and thermal stability of dielectric properties, which makes the phenolic Mannich polybenzoxazine promising candidate as high-temperature dielectric material.

Dielectric properties of CaCu3Ti4O12 ceramics doped by La3+

Abstract XRD, SEM, EDS and XPS were used to study the influence of La3+ on phase structure, microstructure, cationic distribution and cationic oxidation state of CaCu3Ti4O12 ceramics. It was found that donor doping is formed by preferential substitution of La3+ for Ca2+. The concentration of O in the grain is increased and the segregation of Cu into the grain boundary is suppressed effectively by La3+ doping, leading to the decrease and uniform distribution of gain size. The influence of La3+ on dielectric properties of CaCu3Ti4O12 ceramics were investigated also by Novocontrol broadband dielectric spectrometer. It was found that oxygen vacancy-related dielectric relaxation at medium frequency region is suppressed and the corresponding dielectric loss is significantly reduced also. At the same time, high frequency dielectric relaxation is increased obviously, which results in a significant increase of dielectric constant from about 5 × 103 to 2 × 104. The study in this paper shows that donor doping is an effective way to modulate intrinsic point defects, microstructure and then dielectric properties of CaCu3Ti4O12 ceramics.

Electromagnetic and mechanical properties of carbonyl iron powders-PLA composites fabricated by fused deposition modeling

3D printing is an emerging additive manufacturing method for effectively fabricating materials with complex structures. Fused deposition modeling (FDM) is one of the most popular 3D printing techniques, usually used for making thermoplastic parts. However, this method has been rarely considered for designing and fabricating radar wave absorbing structures, which can be very helpful to achieving intricate structures with good mechanical and wave absorbing properties. To verify the validity of this method, carbonyl iron particles filled thermoplastics composites are fabricated by FDM in this study. The morphological, magnetic, electromagnetic and mechanical properties of the composites are investigated by scanning electron microscopy, vibrating sample magnetometer, broad band dielectric spectrometer and universal testing machine. The composites exhibit the hysteretic loops of typical soft ferromagnetism with relatively low remanence, coercive force, and hysteresis losses. The saturation magnetization per unit mass of iron powders of the composites does not have a linear relation with filler contents. The obtained composites materials possess slightly improved tensile strength and significantly improved total elongations than materials obtained by traditional manufacture methods. This 3D printing process will enlighten a rational design of composites with complex shapes, and can also be extended to other thermoplastics based composites, including ABS, PC, and PA.