Measurement Of Dielectric Properties Research Articles

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue-mimicking gel phantom and ex vivo bovine liver and to report on measurements of the temperature-dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20°C-90°C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating was used to develop a calibration between color changes and the temperature to which the phantom was heated. Using a custom, 2.45GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65W applied for 5min or 10min (n=3 samples in each medium for each power/time combination). Broadband (500MHz-6GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range of 22°C-100°C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57°C. Short and long axes of the ablation zone in the phantom (as assessed by the 57°C isotherm) for 65W, 5min ablations were aligned with the extents of the ablation zone observed in ex vivo bovine liver. However, for the 65W, 10min setting, ablations in the phantom were on average 23.7% smaller in the short axis and 7.4 % smaller in the long axis than those observed in ex vivo liver. Measurements of the temperature-dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue-mimicking phantoms provides a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings. However, ablation zone size and shapes in the thermochromic phantom do not accurately represent ablation sizes and shapes observed in ex vivoliver tissue for high energy delivery treatments (65W, 10min). One cause for this limitation is the difference in temperature-dependent thermal and dielectric properties of the thermochromic phantom compared to ex vivobovine liver tissue, as reported in the present study.

Exploring the dielectric loss of Martian regolith in the frequency domain using Zhurong radar data

Martian regolith is one of the primary science objectives of Mars exploration missions. The Rover Penetrating Radar carried by Zhurong rover allows for high-resolution subsurface imaging and in-situ measurements of Martian regolith dielectric properties, which are crucial to advance our understanding of Martian geology and hydrological evolution. While earlier studies have derived dielectric constants for the shallow subsurface, further characterization of subsurface materials requires the determination of attenuation properties. In this study, we applied the centroid-frequency shift method to explore the attenuation property of the Martian regolith in the frequency domain. Lateral attenuation variation was analyzed in detail by integrating subsurface radargram and navigation terrain images. The results show that, within a depth of ∼4 m, the attenuation of radar signal for Zhurong subsurface material is equal to a loss tangent of 0.0079, with a standard deviation of 0.001. Based on the loss tangent value, dielectric permittivity and ground characterization, we preclude the possibility that the regolith is predominantly igneous materials. The lateral variation of the attenuation property could likely be attributed to changes in the proportion of duricrusts, which are heterogeneously distributed along the rover traverse. Our findings offer valuable information for understanding the Martian regolith and its evolution, serving as a important reference for future Mars sample return missions.

An experimental system for detection and localization of hemorrhage using ultra-wideband microwaves with deep learning

Stroke is a leading cause of mortality and disability. Emergent diagnosis and intervention are critical, and predicated upon initial brain imaging; however, existing clinical imaging modalities are generally costly, immobile, and demand highly specialized operation and interpretation. Low-energy microwaves have been explored as a low-cost, small form factor, fast, and safe probe for tissue dielectric properties measurements, with both imaging and diagnostic potential. Nevertheless, challenges inherent to microwave reconstruction have impeded progress, hence conduction of microwave imaging remains an elusive scientific aim. Herein, we introduce a dedicated experimental framework comprising a robotic navigation system to translate blood-mimicking phantoms within a human head model. An 8-element ultra-wideband array of modified antipodal Vivaldi antennas was developed and driven by a two-port vector network analyzer spanning 0.6–9.0 GHz at an operating power of 1 mW. Complex scattering parameters were measured, and dielectric signatures of hemorrhage were learned using a dedicated deep neural network for prediction of hemorrhage classes and localization. An overall sensitivity and specificity for detection >0.99 was observed, with Rayleigh mean localization error of 1.65 mm. The study establishes the feasibility of a robust experimental model and deep learning solution for ultra-wideband microwave stroke detection.

Growth of Single Crystals of (K1-xNax)NbO3 by the Self-Flux Method and Characterization of Their Phase Transitions.

In this study, single crystals of (K1-xNax)NbO3 are grown by the self-flux crystal growth method and their phase transitions are studied using a combination of Raman scattering and impedance spectroscopy. X-ray diffraction shows that single crystals have a perovskite structure with monoclinic symmetry. Single crystal X-ray diffraction shows that single crystals have monoclinic symmetry at room temperature with space group P1211. Electron probe microanalysis shows that single crystals are Na-rich and A-site deficient. Temperature-controlled Raman scattering shows that low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions take place at -20 °C, 220 °C and 440 °C. Dielectric property measurements show that single crystals behave as a normal ferroelectric material. Relative or inverse relative permittivity peaks at ~-10 °C, ~230 °C and ~450 °C with hysteresis correspond to the low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions, respectively, consistent with the Raman scattering results. A conduction mechanism with activation energies of about 0.5-0.7 eV was found in the paraelectric phase. Single crystals show polarization-electric field hysteresis loops of a lossy normal ferroelectric. The combination of Raman scattering and impedance spectroscopy is effective in determining the phase transition temperatures of (K1-xNax)NbO3.

Ferroelectricity Induced by a Combination of Crystallographic Chirality and Axial Vector.

Ferroelectric materials compatible with magnetism and/or conductive properties provide a platform for exploring unconventional phenomena, such as the magnetoelectric effect, nonreciprocal responses, and nontrivial superconductivity. Though recent studies on multiferroics have offered several approaches, the search for magnetic and/or conducting ferroelectric materials is still a challenging issue under the traditional "d0-ness" rule, refusing active d electrons. Here, we propose the emergence of ferroelectricity through a combination of crystallographic chirality and axial vector, accepting even non-d0 magnetic ions. This proposal is demonstrated in quasi-one-dimensional magnetic systems SrM2V2O8 (M = Ni, Mg, and Co). The ferroelectric phase transition is observed by measurements of neutron powder diffraction and dielectric properties in all compositions. Structural analyses and first-principles calculations indicate that these magnetic compounds are identified as proper-type ferroelectrics whose ferroelectric phase transition is achieved by spiral motions of crystallographic screw chains formed by edge-shared MO6 octahedra, considered as the combination of locally defined chirality and axial vector. Computationally predicted magnitude of spontaneous polarization of SrM2V2O8 reaches ∼100 μC/cm2, comparable to that of conventional ferroelectrics, despite the incorporation of non-d0 magnetic elements. The mechanism proposed in this study offers a unique approach to the exploration of new ferroelectrics beyond the traditional paradigms.

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue mimicking gel phantom and ex vivo bovine liver, and to report on measurements of the temperature dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20 - 90 °C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating were used to develop a calibration between color changes and temperature to which the phantom was heated. Using a custom, 2.45 GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65 W applied for 5 min or 10 min ( n = 3 samples in each medium for each power/time combination). Broadband (500 MHz - 6 GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range 22 - 100 °C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57 °C. Short and long axes of the ablation zone in the phantom (as assessed by the 57 °C isotherm) for 65 W, 5 min ablations were aligned with extents of the ablation zone observed in ex vivo bovine liver. However, for the 65 W, 10 min setting, ablations in the phantom were on average 23.7% smaller in short axis and 7.4 % smaller in long axis than those observed in ex vivo liver. Measurements of the temperature dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue mimicking phantoms provide a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings, though ablation zone size and shapes may not accurately represent ablation sizes and shapes observed in ex vivo liver tissue under similar conditions.

Magnetic and dielectric properties of the new YFeO3/BiFeO3 nanocomposite ceramics prepared via reverse chemical co-precipitation followed by spark plasma sintering

New xYFeO3 – (1-x) BiFeO3 (0.0 ≤ x ≤ 1.0) multiferroic composites were prepared successfully via the chemical co-precipitation followed by high energy mechanical blending. For the structural analysis, assessment of phase purity, and characterization of oxidation states, XRD, FTIR and XPS methods were utilized, respectively. Furthermore, morphological investigations and elemental distribution within the composite samples were elucidated through FESEM and TEM imaging techniques. The VSM results indicated that the values of Ms and Mr increase alternately from 0.553emu/g and 0.049emu/g to 1.210emu/g and 0.166emu/g, respectively, with an increase in the YFO content from 20 % to 80 %. These values of Ms do not follow a linear combination of the base phases, and the magnetization of each composite sample is accompanied by an additional value. This additional value may arise from the residual strain and interfacial magnetic and electrical interactions between the parent phases. The measurements of dielectric properties disclosed that the behavior of the samples follows the Maxwell-Wagner polarization. Moreover, the values of ε′ at the frequency of 200 Hz increased from 149 to 303 as the BFO content rose from 20 % to 80 %. In addition, the lowest recorded tanδ value was 0.56 for the 6Y4B sample at 200 Hz. Furthermore, the conductivity measurements showed that the behavior of all samples follows Johnscher's power law.

Study on the high resistivity and resonant frequency characteristics of Eu-doped NiZnCo ferrites

To fulfill the urgent demand for materials suitable for contemporary high-frequency applications, Eu-substituted Ni0.55Zn0.35Co0.1EuxFe2-xO4 (NZCEF, 0 ≤ x ≤ 0.10) composite ferrites were successfully synthesized by a solid-state reaction method, demonstrating characteristics apt for high-frequency functionalities. Detailed examination via SEM and EDS confirmed the compositional purity of these ferrites. Microstructural analysis indicates that the incorporation of europium results in a reduction of the average grain size in NZCEF composites, enhancing the material's densification. Measurements of resistivity and dielectric properties reveal that Eu doping affects the concentration of Fe2+ and Fe3+ ions as well as lattice defects within the ferrite, thereby leading to higher dielectric constants and resistivity (ρ, 6.51 × 108 Ω m). Magnetic analysis confirms that the substitution with Eu ions significantly increases both the coercivity and the ferromagnetic resonance frequency (fr), from 25.7 Oe and 445 MHz to 45.73 Oe and 1.22 GHz, respectively. This improvement is attributed to changes in grain size and domain wall motion. Consequently, Eu3+-substituted NZCEF ferrites exhibit superior electromagnetic properties, making them ideal candidates for advanced high-frequency material applications.

Biosensor with Microchannel for Broadband Dielectric Characterization of Nanoliter Cell Suspensions up to 110 GHz.

Cell dielectric property measurement holds significant potential for application in cell detection and diagnosis due to its label-free and noninvasive nature. In this study, we developed a biosensor designed to measure the permittivity of liquid samples, particularly cell suspensions at the nanoliter scale, utilizing microwave and millimeter wave coplanar waveguides in conjunction with a microchannel. This biosensor facilitates the measurement of scattering parameters within a frequency domain ranging from 1 GHz to 110 GHz. The obtained scattering parameters are then converted into dielectric constants using specific algorithms. A cell capture structure within the microchannel ensures that cell suspensions remain stable within the measurement zone. The feasibility of this biosensor was confirmed by comparison with a commercial Keysight probe. We measured the dielectric constants of three different cell suspensions (HepG2, A549, MCF-7) using our biosensor. We also counted the number of cells captured in multiple measurements for each cell type and compared the corresponding changes in permittivity. The results indicated that the real part of the permittivity of HepG2 cells is 0.2-0.8 lower than that of the other two cell types. The difference between A549 and MCF-7 was relatively minor, only 0.2-0.4. The fluctuations in the dielectric spectrum caused by changes in cell numbers during measurements were smaller than the differences observed between different cell types. Thus, the sensor is suitable for measuring cell suspensions and can be utilized for label-free, noninvasive studies in identifying biological cell suspensions.

High‐throughput combinatorial approach expedites the synthesis of a lead‐free relaxor ferroelectric system

AbstractDeveloping novel lead‐free ferroelectric materials is crucial for next‐generation microelectronic technologies that are energy efficient and environment friendly. However, materials discovery and property optimization are typically time‐consuming due to the limited throughput of traditional synthesis methods. In this work, we use a high‐throughput combinatorial synthesis approach to fabricate lead‐free ferroelectric superlattices and solid solutions of (Ba0.7Ca0.3)TiO3 (BCT) and Ba(Zr0.2Ti0.8)O3 (BZT) phases with continuous variation of composition and layer thickness. High‐resolution x‐ray diffraction (XRD) and analytical scanning transmission electron microscopy (STEM) demonstrate high film quality and well‐controlled compositional gradients. Ferroelectric and dielectric property measurements identify the “optimal property point” achieved at the composition of 48BZT–52BCT. Displacement vector maps reveal that ferroelectric domain sizes are tunable by varying {BCT–BZT}N superlattice geometry. This high‐throughput synthesis approach can be applied to many other material systems to expedite new materials discovery and properties optimization, allowing for the exploration of a large area of phase space within a single growth.image

CaCu3Ti4O12 ceramic via oxalate route: Synthesis, characterization and electrical properties

In this manuscript, a new method for the synthesis of CaCu3Ti4O12 (CCTO) perovskite was adopted via co-precipitation followed by calcination processes. The co-precipitation route was employed to synthesize calcium and copper oxalates precipitated on the TiO2 surfaces and the calcination technique at different temperatures was utilized to follow the single-phase formation. Differential thermal analysis-thermogravimetry (DTA-TG) were used to estimate the proper calcination temperatures and to follow the precursor′s decomposition stages. X-ray diffraction (XRD) revealed the initiation of titanate formation at 700 °C. The complete formation of single-phase was achieved at 1100 °C. In agreement with the XRD measurements, FT-IR spectra confirmed the formation the different phases at different calcination temperatures. The prepared titanate showed giant dielectric properties with values higher than reported in literature. The conductivity measurement indicated semi-conducting properties and revealed a transition agreed well with that obtained in the dielectric properties measurements vs. temperature, attributed to the orientional polarization or change in the entire conduction mechanism from hopping to ionic conduction. The obtained electrical properties enhances the utilization of the entire titanate as capacitors.

Non-contact near-field cavity perturbation method for quantitative dielectric measurement and metallic defect inspection

Low dielectric constant (low-k) materials are essential in electronic industry aiming at new generation high-speed communications. Dielectric constant of these materials are measured by standard procedures and instruments with conventional contact configuration. Non-contact and in-situ techniques for low-k dielectric measurement are highly demanded in practice and worth of investigation. We hereby proposed a near-field microwave probe (NFMP) to accurately measure dielectric constant of low-k samples in a non-contact manner with a quantitative electromagnetic (EM) cavity perturbation theory. An NFMP set was designed, optimized by finite-element method (FEM) and fabricated with handy materials in the lab. Frequency response of the NFMP was tested experimentally and further used for subsequent frequency displacement analysis. Various low-k samples were tested by the non-contact NFMP set and dielectric constant were extracted based on the field perturbation theory. The relative error was obtained less than 0.5 % for low-k materials. The NFMP was then fixed on a micrometer stage and worked in a line-scan mode to inspect conductive defects in a low-k substrate. Both surface and subsurface defects were inspected by analyzing displaced central frequencies. The NFMP system is promising to facilitate quantitative and non-contact dielectric property measurement in electronics.

Solid materials microwave dielectric properties: features of methods practical use

Features of methods practical use for material dielectric properties measurement in different (factory and metrological) laboratories and influence of above mentioned features on measurements results are considered. Results are obtained by Obninsk Research and Production Enterprise “Technologiya” A. G. Romashin radiophysics laboratory and by East-Siberian branch Federal State Unitary Enterprise “Russian metrological institute of technical physics and radio engineering” department of radio engineering measurements. Results of microwave permittivity and loss tangent solid materials measurements are analysed. This investigation made it possible to get additional information about features of standard methods practical use for material dielectric properties measurement, which was absent in literature earlier. In laboratories for measurements used the waveguide resonator and the standardized techniques. The factory laboratory applied a measurement method at the fixed frequency with control in a resonance movement of the plunger, and in metrological laboratory a measurement method with the fixed length of the resonator and measurement at resonant frequencies. Results of measurements showed good reproducibility of results for samples that are meeting method requirements. It was revealed reducing reproducibility of measurements of hygroscopic, heterogeneous samples and in the case of nonobservance of diameter method requirements. Obtained results can be applied for reproducibility improvement of dielectric properties measurements in practical use of considered methods.

Structural Elucidation and Evaluation of Magnetic and Dielectric Properties of Lu–La Co‐substituted M‐Type Hexagonal Ferrites Synthesized by Chemical Co‐precipitation Method

In this research, LuxLaySr1–yFe12–xO19, an M‐type strontium ferrite, is synthesized using the coprecipitation method with precursor chemicals. The samples undergo analysis for structure, morphology, and elemental composition through X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Magnetic and dielectric properties are determined using a vibrating sample magnetometer (VSM) and a dielectric property measurement instrument (LCR), respectively. The primary objective of this study is to enhance the dielectric performance of the samples through rare‐earth element doping. The XRD analysis reveals that the samples display a hexagonal single‐phase magnetoplumbite crystal structure. SEM micrographs illustrate a regular hexagonal structure of the grains. VSM analysis affirms LuxLaySr1–yFe12–xO19 as a hard magnetic material with a high coercivity. As the rare‐earth element content increases, the coercivity of the samples significantly decrease from 2065.3 to 910.3 Oe. Dielectric property analysis demonstrates that augmenting the rare‐earth element (Lu–La) content notably increases the relative dielectric constant of the samples. In the low‐frequency region, the relative dielectric constant ranges from 6.71 × 103 to 1.28 × 105, while in the high‐frequency region, it ranges from 3.09 × 103 to 2.03 × 104. Samples doped with rare‐earth elements exhibit a high dielectric constant and low coercivity, rendering them suitable for applications in electromagnetic shielding materials. This can help reduce interference from magnetic fields on internal components while blocking electromagnetic waves.

Field dependence of the electrocaloric effect in BaTiO3 and Ba(Zr0.12Ti0.88)O3: High-resolution measurements around the phase transition

The electric field dependence of the electrocaloric effect is investigated in BaTiO3 and Ba(Zr0.12Ti0.88)O3 by a direct method with sub-mK temperature resolution. The field dependence of the caloric temperature change ΔT(E) shows a pronounced change within a few Kelvin around the Curie temperature for the first-order phase transition in BaTiO3. The transition from a linear field dependence in the ferroelectric phase over a butterfly-shaped to a quadratic field dependence in the paraelectric phase is compared to predictions of Landau–Devonshire theory. The simultaneous measurement of caloric and dielectric properties further allows for the investigation of the polarization dependence ΔT(P) of the electrocaloric effect. We find clear deviations from the predicted quadratic polarization dependence for temperatures close to the Curie temperature. Ba(Zr0.12Ti0.88)O3 shows in contrast only a slow and gradual change of the field dependence over a broad temperature range as a consequence of its diffuse phase transition.

Compaction pressure effect on the dielectric, DC and AC conductivity of C-130 porcelain

Porcelain insulators can be prepared in a variety of compositions using several different preparation techniques. In the frame of the present work the effect of the applied compaction pressures on the C-130 grade electroporcelain was studied in terms of electrical and dielectric properties. Compaction is a widely used preparation process, nevertheless, a little is known about the effect of the compaction pressure on the final electrical properties of the material. Samples prepared with different compaction pressures (from 70 MPa to 110 MPa; 10 MPa step size) were subjected to a measurement of DC conductivity up to 1200 °C, and a measurement of dielectric properties at room temperature after different firing temperatures. The DC conductivity of the raw samples ranged from ∼10−10 S/m at room temperature to <10−3 S/m at 1100 °C. Temperature dependence of the DC conductivity revealed that the dominant charge carriers were H+ and OH− ions (initial stages of heating) and alkali ions (at high temperatures and during second heating). The DC conductivity of the previously fired samples (at 1100 °C) ranged from ∼10−12 S/m (room temperature) to ∼10−3 S/m (1200 °C). The AC conductivity of the samples ranged from ∼10−7 S/m (samples fired at 1300 °C, measured at low frequencies) to ∼10−3 (raw sample, measured at high frequencies). AC conductivity measurements and dielectric analysis confirmed that the conduction occurred through ion hopping and the bulk boundary conductivity was dominant. The relative permittivity reached 7–8 after firing at 1300 °C at frequencies above 2 MHz.

3D Imaging and Quantitative Subsurface Dielectric Constant Measurement Using Peak Force Kelvin Probe Force Microscopy

AbstractNoninvasive and depth‐sensitive measurements of dielectric properties are becoming of great interest in advanced and complex nanostructured architectures. Here, a straightforward parallel approach applicable in peak force Kelvin probe force microscopy for a 3D measurement of dielectric constants at the nanoscale is demonstrated. The proposed approach features a simultaneous measurement of the mechanical, electrical, and depth‐dependent dielectric properties applied to embedded nanostructures. The findings provide initial elements for further development of experimental dielectric nano‐tomography methods for characterizing buried and embedded systems and dielectric interfaces.

Study on the difference of high frequency dielectric properties of biological tissues measured by air and packed coaxial probe

In this paper, the differences between air probe and filled probe for measuring high-frequency dielectric properties of biological tissues are investigated based on the equivalent circuit model to provide a reference for the methodology of high-frequency measurement of biological tissue dielectric properties. Two types of probes were used to measure different concentrations of NaCl solution in the frequency band of 100 MHz-2 GHz. The results showed that the accuracy and reliability of the calculated results of the air probe were lower than that of the filled probe, especially the dielectric coefficient of the measured material, and the higher the concentration of NaCl solution, the higher the error. By laminating the probe terminal, liquid intrusion could be prevented, to a certain extent, to improve the accuracy of measurement. However, as the frequency decreased, the influence of the film on the measurement increased and the measurement accuracy decreased. The results of the study show that the air probe, despite its simple dimensional design and easy calibration, differs from the conventional equivalent circuit model in actual measurements, and the model needs to be re-corrected for actual use. The filled probe matches the equivalent circuit model better, and therefore has better measurement accuracy and reliability.

Dielectric and optical properties, high temperature conduction, and relaxation behavior of donor-element modified NBST material

The relaxor ferroelectrics (Na0.33Bi0.33Sr0.33) (Ti1-xW0.666x)O3, where 0%≤ x ≤7% (NBST+0W, NBST+3W, NBST+5W, and NBST+7W), were prepared using the solid-state reaction method. X-ray diffraction analysis showed that perovskite structures were formed at room temperature. Microstructural characterization, as well as optical and dielectric property measurements, yielded the following results: substituting Ti4+ with the donor element W6+ led to a decrease in the average grain size, dielectric loss, degree of diffusivity, and affected the temperature Tm. In the case of x = 3% of WO3, the electrical conductivity of NBST improved at high temperatures. However, the compound (NBST+7W) exhibited a low optical gap energy and high electrical conductivity at room temperature. The electrical conductivity curves were fitted by Jonscher power law, which showed that the correlated barrier hopping (CBH) model was the most dominant. Comparison of the imaginary part of impedance and electric modulus revealed that the relaxation of charge carriers in the basic compound NBST+0W occurred at both long and short ranges. However, after doping, the relaxation occurred only at a short range.

Characterization of Nano-Structured Magnesium-Aluminum Ferrites Synthesized by Citrate-Gel Auto Combustion Method

An effort is made to find the solution to the new challenges of modification advancements in ferrite technologies. The hypothetical variation in the structural, magnetic, and electrical properties of cubic spinel magnesium aluminum ferrites introduced by the substitution of doping elements has been rationalized and proven. The outcome of aluminum substitution on the magnesium ferrites has been examined and investigated. Spinel ferrites having compositions of MgAlxFe2-xO4 (x = 0.1, 0.2, 0.3, 0.4) were prepared by the sol-gel auto-combustion method. The prepared sample’s characterization, such as scanning electron microscopy (SEM), DC electrical resistivity, AC electrical resistivity, and dielectric properties measurements, were tested using the respective instruments. The grain size and crystal size of all samples were measured from the micrographs of SEM and XRD Data. It is found that the average grain size is within the range of 300 nm - 550 nm for all different series that are formed, keeping the samples at 1100 °C sintering temperatures. A two-probe method experiment with a temperature range of 30 °C to 500 °C gives data on DC electrical resistivity. The Curie temperature depends on the sintering temperature, and it increases with increasing doping concentration. Also, doping influences grain size, which decreases with increasing concentration. Analyzing the SEM micrographs, it is found that the average grain size must decrease in tendency with increasing Al content. DC electrical resistivity exhibits excellent semiconducting behavior. Frequency dependence, dielectric constant, and dielectric loss factors were measured, keeping the frequency range of 75 Hz to 130 MHz at room temperature. The result shows that the dielectric constant (e) and dielectric loss tangent (tan™) decrease with the increase in frequency, while the AC resistivity and Q-factor increase. Comparing the electrical properties of four compositions, it can be suggested that the mixed ferrite, sample-4 (x = 0.3), shows the highest Q-factor of all at 1100 °C.