Temperature Coefficient Research Articles

Design and Investigation of a High-Performance Quartz-Based SAW Temperature Sensor

In this work, a surface acoustic wave (SAW) temperature sensor based on a quartz substrate was designed and investigated. Employing the Coupling-of-Modes (COM) model, a detailed analysis was conducted on the effects of the number of interdigital transducers (IDTs), the number of reflectors, and their spacing on the performance of the SAW device. The impact of the transversal mode of quartz SAWs on the device was subsequently examined using the finite element method (FEM). The simulation results indicate that optimizing these structural parameters significantly enhances the sensor’s sensitivity and frequency stability. SAW devices with optimal structural parameters were fabricated, and their resonant frequencies were tested across a temperature range of 25–150 °C. Experimental results demonstrate that the SAW temperature sensor maintains high performance stability and data reliability throughout the entire temperature range, achieving a Bode-Q of 7700. Furthermore, the sensor exhibits excellent linearity and repeatability. An analysis of the sensor’s response under varying temperature conditions reveals a significant temperature dependency on its Temperature Coefficient of Frequency (TCF). This feature suggests that the sensor possesses potential advantages for applications in industrial process control and environmental monitoring.

Tl2XY (X, Y = S, Se) monolayers with low lattice thermal conductivity and high thermoelectric performance by full-band approach with four scattering mechanisms

Abstract The low lattice thermal conductivity and high thermoelectric performance of the Janus Tl2SSe monolayer in the temperature region of 300~700 K are identified based on the thermoelectric properties of the Tl2S2, Tl2SSe, and Tl2Se2 monolayers. The transport coefficients for carrier concentrations and temperatures are obtained by solving the linearized Boltzmann transport equation in a full-band electronic structure. Four scattering mechanisms of acoustic deformation potential, optical deformation potential, polar optical phonon, and ionized impurity scatterings are considered. The ionized impurity scattering is recognized as the most important. The lattice thermal conductivity of the Janus Tl2SSe monolayer is substantially smaller than those of the Tl2SSe, Tl2Se2 monolayers with higher symmetry. Moreover, we find that the Janus structures of the Tl2SSe monolayer increase the dielectronic constants and enhance the polar optical phonon scattering, then reduce the power factor to some extent. Therefore, the lattice thermal conductivity actually couples with the transport coefficient and cannot be individually regulated as is usually assumed. However, the ZT value of the Tl2SSe monolayer can still reach 1.77 at 700 K even if the intrinsic concentration and the bipolar effect are included. Therefore, the Tl2SSe monolayer is expected to be a promising candidate for thermoelectric materials.

Photoinduced modulation and the effect of CNT loading on field effect transistor characteristics of CNT/ZnO/PVDF composite.

CNT/ZnO/PVDF polymer composite phototransistor is studied for the effect of CNT loading and the photoinduced modulation on its transfer characteristics. XRD study shows that the induced strain in the composite is due to the addition of CNT to the ZnO/PVDF composite. The percentage of β-phase present in PVDF is estimated through Raman spectroscopy and the composite's spectral response is determined by UV-Vis absorbance spectroscopy. From the DC electrical conductivity study it is found that the percolation threshold for the composites is obtained for 0.3 wt% of CNT, and 0.44 wt % of CNT loading makes the composite conductive. On adding 1 wt% of CNT, the electrical conductivity of the ZnO/PVDF composite increases 40 times (~ 0.2 μS/m). The temperature-dependent DC conductivity shows that the conductivity of the composites changes from variable range hopping (VRH) to band conductance upon an increase in CNT loading above the percolation threshold and exhibits a negative temperature coefficient (NTC). Two terminal photoconductivity studies are done to understand the photo enhancement and sensitivity of all the devices. PE hysteresis studies show that the polarization of the composites increases drastically from 0.05 μC/cm2 below the percolation threshold to 10 - 30 μC/cm2 above the percolation threshold of CNT in the composite. To study the effect of interfacial polarization on photoconductivity, the composite is studied in a three-terminal device format using SiO2 as a gate dielectric. A band diagram analysis of the oxide-composite and CNT/ZnO interface is done to understand the mechanism behind the photoinduced field effect on transfer characteristics and the effect of CNT loading. The switching behavior and decay time under UV illumination are studied to understand the effect of CNT loading and photoinduced polarization. The persistent photoconductivity decreases and the charge collection efficiency of the FET increases as the CNT loading increases.

Ultra-Thin Highly Sensitive Electronic Skin for Temperature Monitoring

Electronic skin capable of reliable monitoring of human skin temperature is crucial for the advancement of non-invasive clinical biomonitoring, disease diagnosis, and health surveillance. Ultra-thin temperature sensors, with excellent mechanical flexibility and robustness, can conformably adhere to uneven skin surfaces, making them ideal candidates. However, achieving high sensitivity often demands sacrificing flexibility, rendering the development of temperature sensors combining both qualities a challenging task. In this study, we utilized a low-cost drop-casting technique to print ultra-thin and lightweight (thickness: approximately 3 µm, weight: 0.61 mg) temperature sensors based on a combination of vanadium dioxide and PEDOT:PSS at room temperature and atmospheric conditions. These sensors exhibit high sensitivity (temperature coefficient of resistance: −5.11%/°C), rapid response and recovery times (0.36 s), and high-temperature accuracy (0.031 °C). Furthermore, they showcased remarkable durability in extreme bending conditions (bending radius = 400 µm), along with stable electrical performance over approximately 2400 bending cycles. This work offers a low-cost, simple, and scalable method for manufacturing ultra-thin and lightweight electronic skins for temperature monitoring, which seamlessly integrate exceptional temperature-measuring capabilities with optimal flexibility.

Numerical Analysis of a Two-Layer PCM Based Battery Thermal Management System for Different Material Properties

The design and numerical analysis of the two-layer PCM (Phase Change Material)-based thermal management system for a 18650-type lithium-ion battery have been performed. In relation to simulation, the coefficient of thermal conductivity and melting temperature of the first layer of PCMs are varied. Other parameters are made identical to that of the next layer's parameters in order that the generation of two different layers of PCMs can be attained: PCM-1 and PCM-2. To obtain a more realistic approach in the numerical analysis, the battery thermal model was created in the COMSOL-MATLAB interface using the experimental internal resistance data obtained for 18650 type Li-ion batteries in the literature. While a cheaper and more accessible material with a thermal conductivity of 0.2 W/mK and a melting point of 50 °C was used in the PCM-2 layer, the thermal conductivity was changed to 0.2; 1 and 5 W/mK in the PCM-1 layer; and the melting point was changed to 30, 40 and 50 °C. In this way, for PCM layers with different thickness (tpcm), the system was optimized at two different discharge rates, 5C and 7C. As a result of the numerical analysis, it was determined that the optimum tpcm, kpcm,1 and Tm values for the 5C discharge rate were 2 mm, 0.2 W/mK and 40 °C, respectively; and the optimum tpcm, kpcm,1 and Tm values for the 7C discharge rate were 4 mm, 5 W/mK and 40 °C, respectively.

Unveiling the low‐temperature oxidation chemistry of dipropyl carbonate

AbstractDialkyl carbonates (DACs) own an environmentally friendly synthesis route, making them potential candidates as alternative fuels. However, for DACs to be widely accepted as an alternative fuel, a comprehensive understanding of their combustion behavior is essential. Dipropyl carbonate (DPrC) represents a transition from short‐chain to mid‐chain carbonates, understanding its combustion behaviors holds significance in unraveling the combustion chemistry of carbonates. In this study, the oxidation of DPrC was investigated with the initial fuel mole fraction of 0.5% at three equivalence ratios of 0.5, 1.0, and 2.0 within a temperature range of 550–1100 K in a jet‐stirred reactor for the first time. Gas chromatography was utilized for the quantitative detection of reactants, intermediates, and products. A detailed DPrC mechanism was first developed, and good agreements between measurements and simulations were obtained. A notable negative temperature coefficient (NTC) behavior was first observed in the oxidation of DACs. Such NTC phenomenon occurred at fuel‐lean conditions in the temperature range of 620–660 K, while only a weak low‐temperature consumption was observed at the stoichiometric condition. Kinetic modeling studies showed that this unique low‐temperature chemistry of DPrC can be attributed to the differences in the RO2 isomerization reactions between DPrC and short‐chain DACs. The RO2 isomerization via a six‐member ring transition state could happen in DPrC oxidation but not in dimethyl carbonate and diethyl carbonate oxidation, due to the different fuel molecular structure. Therefore, the subsequent reaction pathways via QOOH → O2QOOH → HO2Q = O + OH → OQ = O + OH were promoted and two OH radicals were released in this process. Moreover, it is conceivable that mid or long‐chain DACs could also exhibit an NTC phenomenon due to the increased potential for RO2 isomerization via a six‐ or seven‐member ring transition state, thereby increasing the likelihood of RO2 isomerization occurrence.

Ta doping effect on microstructure and microwave dielectric properties of CoNb2O6‐based ceramics and mechanism study

AbstractAs communication technology continues to evolve, 5G technology is becoming more mature, and 6G technology is steadily advancing. Microwave equipment is moving toward high frequency, miniaturization, low loss and high temperature stability, and microwave dielectric ceramics have been deeply applied in this field. To elevate the Q × f value of CoNb2O6 system, Ta5+ was introduced into CoNb2O6, and CoNb2‐xTaxO6 (0.0 ≤ x ≤ 0.8) ceramics were prepared by the traditional solid‐phase method. By X‐ray diffraction, it was observed that at x = 0.8, in addition to a single niobium ferrite phase, information of tantalate phase also appeared. Raman spectral detection and group theory analysis indicate that Ag(2) and Ag(3) modes are the dominant Raman vibrations at ≈873 cm−1. Furthermore, the polarization rate affects the εr value, and the bond energy of Nb/Ta‐O and the recovery force characterized by the average deformation of the [Nb/TaO6] octahedron are the key elements influencing the temperature coefficient of the resonance frequency (τf). The internal strain, ordered induced size, and chemical bonding valence of ionic valence states are the key factors that can increase the Q × f value. Moreover, the introduction of ions with lower electronegativity leads to an enhanced electronic compensation of oxygen vacancies, which also reduces the dielectric loss. This paper enriches the theory related to low dielectric loss and shows that CoNb1.8Ta0.2O6 (εr = 21.4832, Q × f = 100723 GHz, τf = ‐61.38 ppm/°C) ceramics with superior microwave dielectric properties are expected to be used in wireless communication devices.

Enhancing performance of microbolometers by utilizing low-temperature polycrystalline silicon

In response to the urgent need for advanced noncontact temperature sensing technologies to mitigate pandemic transmission, there has been a notable surge in global demand. Thermal cameras, combined with infrared sensors, are critical not only for high-resolution imaging but also for cost-effective commercialization. Amorphous silicon-based microbolometers offer advantages in terms of integration and cost compatibility with conventional silicon processes. However, they suffer from limitations in their electrical properties, particularly in the noise-equivalent temperature difference. This study examines the effectiveness of low-temperature polycrystalline silicon (poly-Si) as an active material for microbolometer cells compared to amorphous silicon, focusing on improving the temperature coefficient of resistance (TCR) and lowering the noise density. Our investigation reveals that various parameters, such as dehydrogenation temperatures ranging from 350 to 550 °C, diverse laser annealing techniques (including single, step and multishot methods), and laser power density levels ranging from 150 to 300 mJ/cm2, influence the grain size trends of poly-Si. Using these methods, we produced poly-Si films with grain sizes ranging from 15 to 40 nm, which were used as the active layer in bolometer cells. The final part of our study assessed the TCR and noise density in devices with different poly-Si grain sizes. The TCR/noise density ratio was 3.5 times better in poly-Si devices compared to amorphous silicon devices. This study evaluates poly-Si as an active material for microbolometers, paving the way for future research and development in next-generation infrared sensor technology.

Ozone Doping and Negative Temperature Response in the Explosion Limits of Ethylene-Oxygen Mixtures.

In this work, effects of ozone (O3) addition on ethylene-oxygen (C2H4-O2) mixtures are computationally studied through the explosion limit profiles. The results show that the addition of minute quantities of ozone (with a mole fraction of 0.06% in the oxidizer) shifts the explosion limit of the C2H4-O3-O2 mixtures to the low-temperature regime. Further increases in the ozone concentration gradually strengthen the negative temperature coefficient (NTC) behavior at the second limit. That is because the explosion limit is primarily controlled by the ethylene ozonolysis reaction, and both the sensitivity analysis and chemical reaction rate perturbation method reveal specific kinetic reasons. Furthermore, it is shown that with the increasing equivalence ratio, the explosion limit curve with minute ozone addition rotates counterclockwise around a crossover point, while the explosion limit curve becomes complicated and the NTC behavior appears on the second limit with larger quantities of ozone addition. Furthermore, the effects of dilutions of nitrogen (N2), argon (Ar), carbon dioxide (CO2), and water (H2O) on the explosion limits are also studied. To elucidate the different wall elimination effects of different explosion limit regimes, the impacts of surface reactions of six radicals (H, O, OH, HO2, H2O2, and HCO) have been examined and the dominant radicals are found to be H and HO2. The H radicals significantly influence the first explosion limit, while the HO2 radicals impact the entire explosion limit.

Mesoscopic shear evolution characteristics of frozen soil-concrete interface

The mechanical properties of frozen-concrete interfaces affect the stability and durability of engineering structures in cold regions. To investigate these properties, laboratory tests and numerical simulations were conducted to study the mesoscopic evolution of the shear stress-displacement relationship and the shearing process at the interface. The direct shear tests were performed at different environmental temperatures (−2 °C, −5 °C, and −10 °C) and normal stresses (100 kPa, 200 kPa, and 300 kPa) on the frozen soil-concrete interface, and Particle Flow Code (PFC) model of direct shear was developed. The mesoscopic parameters (particle displacement, rotation, force chain, stress, coordination number, porosity, fabric, etc.) of the interface during shearing were simulated using the PFC model. Moreover, the relationship among the interface temperature, cohesion, and friction coefficient was determined based on experimental data, and the accuracy of the PFC model was verified using previous experimental data. The results of the PFC shear model aligned well with those of the laboratory test, and the formation of shear bands was simulated well. The displacement of the soil particles on the upper layer outside the shear zone was uniform, and the direction was the same, whereas the particles inside the shear zone showed significant differences in the dislocation and rotation of the soil particles. The force chain, stress field, coordination number, and porosity were similar in the shear process and showed a concentrated distribution in the opposite direction of the shear motion, which reflected the consistency of the microcosmic response of the particles under the action of macroscopic external forces. The regression equations for the temperature, cohesion, and friction coefficient in this study can be used to simulate the shear behavior of frozen soil-concrete interfaces under different temperatures and normal stresses.

A Sub-1 ppm/°C Reference Voltage Source with a Wide Input Range

With the continuous advancement of electronic technology, the application of high-voltage integrated circuits is becoming increasingly prevalent in fields such as power systems, medical devices, and industrial automation. The reference circuit within high-voltage integrated circuits must not only exhibit insensitivity to temperature variations but also maintain stability across a broad voltage supply. This paper presents a bandgap reference (BGR) source capable of operating over a wide input range. This BGR employs a high-order curvature compensation method to eliminate nonlinear voltage terms, resulting in minimal temperature drift. The circuit achieves an impressive temperature coefficient (TC) of 0.88 ppm/°C over a temperature range from −40 °C to 130 °C. To ensure stable operation within a 4–40 V range, the design incorporates a pre-regulation circuit that stabilizes the supply voltage of the BGR core at a fixed value, thereby enhancing the ability to withstand variations in power supply voltage.

Laser‐Induced Graphene Smart Textiles for Future Space Suits and Telescopes

AbstractNovel materials with high electrical, optical, and thermal functionalities are crucial in next‐generation space missions. Astronauts’ well‐being demands continuous health monitoring, while stray light suppression and heat dissipation are vital for space telescopes. Here, it is demonstrated that laser‐induced graphene (LIG), patterned with femtosecond laser pulses, serves as a versatile material for temperature/strain sensing, stray light absorption, and heat management for smart spacesuits and telescopes. LIG exhibits a superior temperature coefficient of resistance (−0.068% °C⁻¹), gauge factor of 454, optical absorption (97.57%), and heat diffusivity (6.376 mm2 s−1) via a single platform. Furthermore, thermal‐vacuum tests confirm LIG's reliability and readiness for space missions. Under vacuum conditions (≈10−3 Torr) and repeated temperature changes ranging from −20 to 60 °C over a period of ≈40 h, the temperature/strain sensor, and optical absorbers maintain the functionality.

Elastic mechanical thermodynamic and thermoelectric properties of pristine and titanium doped Mg2Si: a density functional theory study

Herein, we report a systematic investigation of the effect of Titanium doping on the structural, elastic, mechanical, thermodynamic, and thermoelectric (TE) dynamics of Mg2Si Compounds using first-principle investigation. The present study has been carried out using the full potential linearized augmented plane wave method as implemented inWien2kcode undermBJexchange potentials. The investigations revealed that Mg2-xTixSi compounds have structural stability with cubic phase (Fm-3msymmetry) and possess degenerate semiconducting nature. The analysis of elastic constants revealed mechanical stability of the investigated compounds following Born criteria. Thermodynamic investigations have been carried out in the temperature range of 100-1500 K at zero pressure and the quantities like heat capacity, Debye temperature, Grüneisen constant, and thermal expansion coefficient have been critically analyzed. Lastly, the TE performance of Mg2-xTixSi compounds has been predicted by estimating the thermopower (S2σ) and TE figure of merit (zT) in the temperature range of 300-1500 K. The predicted value ofzTmaxfor Mg2-xTixSi compound is 0.67 at 800 K forx= 0.25 titanium content, suggesting materials promising application for TE energy harvesting and mechanical devices.

Improving turbulence modeling for gas turbine blades: A novel approach to address flow transition and stagnation point anomalies

Accurate prediction of temperature and Heat Transfer Coefficient (HTC) distributions over gas turbine blades is crucial for the design process and life assessment of these components. Numerical studies of flow over gas turbine blades face significant challenges in accurately simulating two complex phenomena: (1) the transition of flow from laminar to turbulent, and (2) stagnation point flow at the leading edge. Many turbulence models tend to overpredict the temperature on turbine blades, leading to incorrect identification of hot-spot regions and, consequently, erroneous estimations of blade life. This paper investigates the performance of various turbulence models in simulating flow and heat transfer over gas turbine vanes. The study includes three full turbulence models, i.e., Spalart-Allmaras (SA), Shear Stress Transport k−ω (SST-kw), and v2−f (V2F), as well as two transitional models, i.e., Transition SST (Trans-SST) and k−kL−ω (k-kl-w). Simulation results indicate that the v2−f, Trans-SST, and k−kL−ω models can detect flow transition. However, the transition length and onset location predicted by the Trans-SST and k−kL−ω models do not align with experimental data. Conversely, the v2−f model suffers from over-predictions at the leading edge due to stagnation point anomaly. To address these issues and due to capacities of the V2F model, this study proposes two modifications to enhance the performance of the V2F model. First, the production term of turbulent kinetic energy is redefined to mitigate the stagnation point anomaly. Second, the model is recalibrated to improve the prediction of flow transition. The new model, named the Production Modified V2F (PMV2F) model, shows promising results in predicting temperature and heat transfer coefficients.

Deciphering the Conformations of Glutathione Oxidized Peptide: A Comparative NMR Study in Solution and Solid-State Environments.

Glutathione (GSH) and its oxidized dimer (GSSG) play an important role in living systems as an antioxidant, balancing the presence of reactive oxygen species (ROS). The central thiol (-S-S-) bond in GSSG can undergo free rotation, providing multiple conformations with respect to the S-S bridge. The six titratable sites of GSSG, which are influenced by pH variations, affect these conformations in solution, whereas in solids, additionally crystal packing effects come into play. In view of differing reports about the structure of GSSG in literature, we have here conducted an extensive reexamination of its conformations using NMR, and contrasting results have been obtained for solution and solid state. In solution, the existence of more than one antiparallel orientation of the monomer unit with different hydrogen bonding schemes has been indicated by NOE and amide temperature coefficient results. On the other hand, in the solid-state, a 1H-1H double-quantum (DQ) to 13C single-quantum (SQ) correlation study has confirmed a parallel orientation, consistent with the reported X-ray crystal structure. Experimentally assigned solid-state NMR resonances have been validated using GIPAW calculations incorporated in the Quantum ESPRESSO package.

Effect of milling time on structural and electrical properties of thermomechanically synthesized of Ba0.1 (Bi0.45Na0.45)TiO3 nanoceramics for ferroelectric random-access memory device

Lead-free Ba0.1(Bi0.45Na0.45)TiO3 (BBNTO) nanoceramics were synthesized using high-energy ball milling, followed by a solid-state reaction method. XRD analysis of the microstructure indicated the formation of tetragonal symmetry. The crystallite size of the nanoceramic powder decreased from ∼ 28 nm to 10 nm after milling for 0, 30, 60, and 90 hours. The dielectric properties of the nanoceramics showed significant improvement, with a diffuse phase transition occurring around 80 °C). The dielectric constant increased with temperature across various frequencies, reached a maximum value at approximately at temperature ∼ 380 °C. At lower temperatures and higher frequencies, the relative permittivity and tangent loss depend on the crystallite size and milling duration. Impedance spectroscopy data analysis revealed size-dependent impedance characteristics and dielectric relaxation. The ac conductivity plot adhered to the Arrhenius relation, and the calculated activation energy confirmed the negative temperature coefficient of resistance (NTCR) behavior. P-E loops confirmed ferroelectric properties, indicating potential for use in future ferroelectric-based storage devices.

Chemically driven BaTiO3–CoFe2O4 nanocomposite with strong dielectric and low leakagecharacteristics for electrocatalytic water splitting reaction

The switchable electronic properties at the surface of ferroelectric nanomaterials offer possibilities for electrocatalytic hydrogen and oxygen evolution reactions, HER and OER respectively. Here, 0.5(BaTiO3)-0.5(CoFe2O4) (abbreviated as BTCF0.5) are prepared chemically. The material shows a high dielectric constant in the order of 107. Nyquist plot is consistent with non-Debye-type and negative temperature coefficient of resistance (NTCR) characteristics with low leakage current. BTCF0.5 shows superior electrocatalytic HER and OER with a low overpotential of ∼156 and ∼284 mV at current density10 mA/cm2 along with Tafel slopes of 43.37 mV/dec and 41.52 mV/dec respectively. The stability of the electrocatalyst is checked through a chronoamperometry test and up to 1000 cycles of CV both for HER and OER operations. The non-traditional behavior of the nanocomposite may make it highly desirable for usage in numerous renewable and sustainable energy-related applications in the present-day scenario.

A simple picowatt 7.6 ppm/°C, 0.029 %/V line sensitivity fully-CMOS voltage reference with DIBL cancelation

In this paper, a 4-transistor sub-one-volt voltage reference with picowatt power consumption is presented. To achieve ultra-low power consumption and low-voltage operation, all transistors are designed to operate in subthreshold region. By proper design of the circuit, DIBL effect is also compensated to enhance temperature coefficient of the circuit and line sensitivity. The proposed circuit consists of only four different transistors (i.e. thick oxide, native VTH, medium VTH) in a self-biased scheme such that eliminates the need for any start-up circuit. A prototype of the proposed circuit that generates a 341-mV voltage reference is designed and simulated in a standard 0.18-µm CMOS technology. The proposed reference circuit exhibits an average temperature coefficient of 7.6 ppm/°C across all process corners while the total power consumption is as low as 249 picowatt. The average line sensitivity of the circuit is 0.029 %/V within a wide supply range of 0.6 to 3.3 V. Ultra-low power consumption and line sensitivity, and excellent thermal stability render it ideal for integration into RFID and IoT applications.

A Compact V-Band Temperature Compensation Low-Noise Amplifier in a 130 nm SiGe BiCMOS Process.

This paper presents a compact V-band low-noise amplifier (LNA) featuring temperature compensation, implemented in a 130 nm SiGe BiCMOS process. A negative temperature coefficient bias circuit generates an adaptive current for temperature compensation, enhancing the LNA's temperature robustness. A T-type inductive network is employed to establish two dominant poles at different frequencies, significantly broadening the amplifier's bandwidth. Over the wide temperature range of -55 °C to 85 °C, the LNA prototype exhibits a gain variation of less than 1.5 dB at test frequencies from 40 GHz to 65 GHz, corresponding to a temperature coefficient of 0.01 dB/°C. At -55 °C, 25 °C, and 85 °C, the measured peak gains are 25.5 dB, 25 dB, and 24.4 dB, respectively, with minimum noise figures (NF) of 3.0 dB, 3.5 dB, and 4.2 dB, and DC power consumptions of 22.3 mW, 27.6 mW, and 34.4 mW. Moreover, the total silicon area of the LNA chip is 0.37 mm2, including all test pads, while the core area is only 0.09 mm2.

Analysis of the Sr2GdTi2Nb3O15 ceramic: Investigation into its structural properties and complex impedance spectroscopy

In this study, we successfully synthesized tetragonal tungsten bronze with the nominal formula Sr2GdTi2Nb3O15 and systematically examined of its structure, dielectric, and electrical properties. The material was synthesized through the solid-state reaction technique at a temperature of 1350 °C. The formation of the tetragonal tungsten bronze in the P4/mbm space group was verified via Rietveld refinement using X-ray diffraction data. The electrical characteristics of the ceramic were examined using non-destructive complex impedance spectroscopy (CIS) across a range of frequencies (10–106 Hz) at various temperatures. The real component of impedance (Z') displayed a decrease with rising frequency, suggesting a negative temperature coefficient of resistance (NTCR) for this sample. The Cole-Cole plot of the compound exhibits two semicircles, with the compound's resistance gradually decreasing as the temperature increased. Moreover, the activation energy (Ea) was found to be approximately 0.9 eV, which confirms that oxygen vacancies are responsible for the observed relaxation behavior. Complex modulus analysis confirmed the presence of non-Debye relaxations. These results contribute to a thorough comprehension of the structural and electrical characteristics of Sr2GdTi2Nb3O15, opening avenues for potential applications in diverse electronic devices.