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Öğe AAO-Assisted Nanoporous Platinum Films for Hydrogen Sensor Application(Mdpi, 2023) Sener, Melike; Sisman, Orhan; Kilinc, NecmettinThe effects of the porosity and the thickness on the ability of hydrogen sensing is demonstrated through a comparison of compact and nanoporous platinum film sensors. The synthesis of anodic aluminum oxide (AAO) nanotubes with an average pore diameter of less than 100 nm served as the template for the fabrication of nanoporous Pt films using an anodization method. This was achieved by applying a voltage of 40 V in 0.4 M of a phosphoric acid solution at 20 degrees C. To compare the film and nanoporous Pt, layers of approximately 3 nm and 20 nm were coated on both glass substrates and AAO templates using a sputtering technique. FESEM images monitored the formation of nanoporosity by observing the Pt layers covering the upper edges of the AAO nanotubes. Despite their low thickness and the poor long-range order, the EDX and XRD measurements confirmed and uncovered the crystalline properties of the Pt films by comparing the bare and the Pt deposited AAO templates. The nanoporous Pt and Pt thin film sensors were tested in the hydrogen concentration range between 10-50,000 ppm H-2 at room temperature, 50 degrees C, 100 degrees C and 150 degrees C. The results reveal that nanoporous Pt performed higher sensitivity than the Pt thin film and the surface scattering phenomenon can express the hydrogen sensing mechanism of the Pt sensors.Öğe Adsorption of Phthalocyanines on Stoichiometric and Reduced Rutile TiO2(110)(Electrochemical Soc Inc, 2020) Kilinc, Necmettin; Ozturk, Zafer Ziya; Berber, SavasWe report ab initio density functional theory calculations for the metal-free phthalocyanine (H2Pc) and zinc phthalocyanine (ZnPc) molecules adsorbed on rutile titania TiO2(110) stoichiometric and reduced surface. The hybrid nanostructures that combine titania surfaces with organic molecules help to improve the applications for both the titania surface and the organic molecule. We determine the atomic structures for all possible adsorption sites through total energy calculations and atomic structure optimizations. We find that the surface oxygen atoms play a crucial role in determining the best adsorption position and adsorption energies. Charge transfer occurs from the phthalocyanine to the surface. The electronic structure of the hybrid system indicates the appearance of surface states in the energy gap of the bare surface. We univocally determined that these new states involve N atoms and are originated only from the surface atoms with no bulk contribution.Öğe Dealloyed nanoporous platinum films: synthesis, characterization, and hydrogen sensing properties(Frontiers Media Sa, 2025) Sener, Melike; Altuntepe, Ali; Zan, Recep; Kilinc, NecmettinNanoporous platinum (Pt) films are synthesized at room temperature using a straightforward and cost-effective dealloying technique. This method is suitable for producing various nanoporous materials for diverse applications. Copper (Cu) atoms in the PtCu alloy films were selectively dissolved in a nitric acid solution, at varying times, to obtain nanoporous films. PtCu alloy thin films were then deposited onto a glass substrate utilizing the magnetron co-sputtering method with approximately 50 nm thickness. After 20 h dealloying in the acid solution, the residual Cu content in the alloy was less than 1% (atomic rate), and a regular nanoporous Pt structure was observed. The hydrogen detection properties of the nanoporous Pt films thus produced were investigated at various temperatures within a concentration range between 10 ppm and 5% hydrogen. The results demonstrated that a very high sensor response of 64 was obtained for the first exposure to 1% hydrogen at 150 degrees C, but the nanoporous Pt sensor resistance did not return to the baseline resistance. To utilize this nanoporous Pt film as a reversible hydrogen sensor, the film must be pre-exposed to hydrogen. After pre-exposure, the sensor response of the as-prepared nanoporous Pt was approximately 4.5, resulting from exposure to 1% hydrogen at 150 degrees C, and the limit of detection was lower than 10 ppm. Data regarding the mechanism of the nanoporous Pt sensor device were clarified through surface scattering. The main contributions of this research are that sensing nanoporous film has a high surface-to-volume ratio, the sensor exhibited a very high initial response (similar to 64) to 1% hydrogen at 150 degrees C, the sensor mechanism is governed by surface scattering, and pre-exposure to hydrogen is needed for reversible sensing operation in practical usage.Öğe Electrical and NO2Sensing Properties of a Series of Liquid Crystalline Porphyrins(Electrochemical Soc Inc, 2020) Kilinc, Necmettin; Ahsen, Ali Sems; Ozturk, Zafer ZiyaThe electrical and NO(2)sensing properties of a series of porphyrin derivatives (PPC12, PPC16, ZnPPC12) were studied within wide temperature range from 293 to 423 K under the N(2)gas flow and in the frequency range from 1 kHz to 1 MHz for ac electrical measurements. The dc conductivities and the activation energies were found to be in the range of 10(-13)-10(-12)S cm(-1)at the room temperature and 0.46-1.03 eV respectively. The increased C number in the alkyl chain and addition of metal ion to the porphyrin causes a decrease in the conductivity. The ac conductivity was well represented by the power law form A omega(s). The s parameter depending on temperature was varied 0.79-1.2. The conduction mechanism for all porphyrins could be related to small polaron tunneling (SPT) model. As an application, the NO(2)sensing properties of ZnPPC12 were investigated depending on temperature.Öğe Enhancing high sensitive hydrogen detection of Bi2O3 nanoparticle decorated TiO2 nanotubes(Elsevier Science Sa, 2024) Isik, Esme; Tasyurek, Lutfi Bilal; Tosun, Emir; Kilinc, NecmettinAn electrochemical anodization technique was used to create a hydrogen gas sensor based on TiO2 nanotubes decorated with bismuth oxide (Bi2O3). Bismuth nitrate pentahydrate (Bi(NO3)3 center dot 5H2O) was employed as the source material for Bi2O3. The resulting nanotubes were annealed at 500 degrees C, revealing an amorphous structure with a mixed phase of rutile and anatase. Platinum (Pt) electrodes, with a thickness of 100 nm, were coated onto the Bi2O3@TiO2/Ti and TiO2/Ti structures for sensor testing. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM) were used to examine the structural, morphological, and surface properties of the Bi2O3@TiO2 and TiO2 nanotubes. The hydrogen sensing properties of the Pt/Bi2O3@TiO2/Ti and Pt/TiO2/Ti devices were evaluated at room temperature, with hydrogen concentrations ranging from 1000 ppm to 10 %. The I-V characterization of the sensor devices under 1 % H2 exhibited typical Schottky-type behavior. Remarkably, the Pt/Bi2O3@TiO2/Ti structure demonstrated a sensor response 1 x 107 times higher than that of in a dry air environment when the same voltage was applied under up to 1 % H2 conditions. The uniform dispersion of Bi2O3 nanoparticles throughout the structure contributed to the enhanced sensor response in the presence of H2.Öğe Enhancing the performance of TiO2 nanotube-based hydrogen sensors through crystal structure and metal electrode(Pergamon-Elsevier Science Ltd, 2024) Tasyurek, Lutfi Bilal; Isik, Esme; Isik, Ibrahim; Kilinc, NecmettinIn this research, the effect of metal electrodes and crystalline phase on gas detection of titanium dioxide (TiO2) nanotube-based hydrogen (H2) sensors was investigated. TiO2 nanotubes were produced using glycerol-based electrolyte and annealed at 300 degrees C and 700 degrees C to change the anatase and rutile crystalline phases, respectively. TiO2 nanotubes were coated by platinum (Pt), palladium (Pd), gold (Au) and silver (Ag) electrodes to fabricate metal/TiO2 nanotubes Ti H2 sensor devices and then the current-voltage (I-V) characteristics were investigated at room temperature. The structural properties of TiO2 nanotubes were characterized by SEM, FE-SEM, XRD, and Raman techniques. The H2 detection properties of the sensors were examined at the 1000 ppm - 5% H2 concentration range. The crystal structure and metal electrodes are the main factors that affect the H2 sensing properties of TiO2 nanotube-based sensors. The effect of crystal forms on sensitivity was not the same as for metal electrodes. The underlying sensing mechanisms for different types of metal electrodes and crystal structures are discussed and the relevance of their sensing performance to nanotubes and electronic properties is investigated. In addition, discussion of each metal electrode and crystal structure will make important contributions to the development of H2 sensors. The Pd-coated device annealed at 700 degrees C showed the best detection performance.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Highly Sensitive and Selective Detection of Dimethyl Methyl Phosphonate with Copolymer-Based QCM Sensors(Wiley-V C H Verlag Gmbh, 2024) Ozturk, Sadullah; Kosemen, Arif; Sen, Zafer; Tuna, Suha; Bayazit, Sahika Sena; Kilinc, NecmettinIn this work, the volatile organic compounds (VOCs) sensing properties of a quartz crystal microbalance (QCM) transducer coated with six different poly(3-methylthiophene) (P3MT) copolymerized with polypyrrole (PPy) are investigated. The sensor preparation involves the electrochemical deposition of P3MT, PPy, and P3MT-co-PPy on Au-coated QCM transducers by electrochemical deposition techniques with a three-electrode cell. The structural properties of the copolymer films are characterized using scanning electron microscopy, and their oxidation/reduction behavior is investigated through cyclic voltammetry. The copolymer-based QCM sensors exhibit high sensitivity and selectivity to dimethyl methyl phosphonate and benzonitrile, even at low concentrations (<1 ppm) at room temperature. Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms are studied to understand the VOCs sensing mechanism machine learning classification algorithms including quadratic discriminant (QD), neural nets, K-nearest neighbors, linear discriminant, and support vector machines are applied to classify the sensor responses for the 12 different analytes. With the help of machine learning algorithms, tested analytes are successfully classified into their groups. The highest accuracy of 97.34% is achieved using the QD method. The developed sensor, combined with machine learning algorithms, shows promising potential for accurate and reliable detection and classification of VOCs.Öğe Highly sensitive hydrogen sensing properties of Pt-Pd alloy thin films on a flexible substrate(Iop Publishing Ltd, 2025) Kilinc, NecmettinIn the present study, the thin films of platinum-palladium (Pt-Pd) alloy with various compositions are prepared on a flexible polyamide substrate by using the magnetron co-sputtering technique. The atomic Pd content in the alloy was varied from 25% to 63% and the Pt-Pd alloy film thickness was approximately 2 nm. The Pt-Pd alloy thin films were tested in a wide range of hydrogen concentrations from 10 ppm to 4% hydrogen at various temperatures between room temperature to 200 degrees C. The hydrogen sensing mechanism of Pt-Pd alloy thin films is dominated by Pt atoms in the alloy and could be explained by surface scattering. The highest sensor response ( triangle R/RH ) is received as about 8.1% for Pt50Pd50 alloy thin films during exposure to 1000 ppm hydrogen at 50 degrees C. The sensor response and the response time of all Pt-Pd alloy thin films decreased with rising temperature in the measurement temperature range. Another result of this study is that Pt-Pd alloy thin film sensors require oxygen in the working environment to achieve both high sensor response and full recovery. As a summary, Pt-Pd alloy thin film sensors show high sensitivity, hysteresis free, low temperature operation and selective to hydrogen.Öğe Hybrid liquid crystalline zinc phthalocyanine@Cu2O nanowires for NO2 sensor application(Elsevier Science Sa, 2021) Sisman, Orhan; Kilinc, Necmettin; Akkus, Unal Ozden; Sama, Jordi; Romano-Rodriguez, Albert; Atilla, Devrim; Gurek, Ayse GulA novel organic-inorganic hybrid conductometric NO2 sensor has been introduced by depositing liquid crystalline zinc oktakisalkylthiophthalocyanine [(C6S)(8)PcZn] on the surface of Cu2O nanowires. Cu2O nano wires were synthesized by electrochemical anodization of Cu films on glass substrates. Surface structures of bare Cu2O and (C6S)(8)PcZn@Cu2O nanowires hybrid structures were monitored by scanning electron microscope (SEM). UV-vis spectrophotometer measurements revealed the heterostructure formation by comparing the absorption profiles of bare Cu2O nanowires, (C6S)(8)PcZn thin film, and (C6S)(8)PcZn@Cu2O hybrid nanowires. The interdigitated transducers (IDT) were used for conductometric gas measurements. The sensing properties of all samples were investigated towards 500 ppb, 1 ppm, 2 ppm, and 5 ppm NO2 under dry airflow in 30 degrees C, 50 degrees C, 100 degrees C, and 150 degrees C. The measurements at 150 degrees C were repeated for (C6S)(8)PcZn film and hybrid sample using the same concentrations of NO2 gas under 38 % relative humidity airflow. In addition, selectivity of hybrid sensor was confirmed with carbon monoxide (CO), hydrogen (H-2) and ethanol (C2H5OH) measurements. Our density functional theory calculations indicate that S atoms play a crucial role in improving the sensor response. The sensing properties and sensing mechanisms of samples were compared and discussed.Öğe Hydrogen detection and electrical properties of titanium silicate Schottky diode fabricated by RF-magnetron sputtering method(Pergamon-Elsevier Science Ltd, 2025) Tasyurek, Lutfi Bilal; Kilinc, NecmettinIn this study, the electrical characterization of Schottky contact produced by coating TiSiO4 from the perovskite like layered family on p and n type Si by using RF-magnetron sputtering method was investigated depending on gas atmosphere and temperature. The morphological structure of the TiSiO4 thin film was examined by XRD analysis, FE-SEM images, and EDX spectrum. According to AFM images, the average roughness was found to be 0.811 nm. Temperature dependent I-V and AC characteristics of p-Si/TiSiO4 and n-Si/TiSiO4 devices were measured under dry air flow. In addition, frequency dependent C-V measurements of the devices were performed to investigate the capacitance properties of the scheelite-type interface. Also, the sensor response obtained with this device was as high as 267.7. Hydrogen sensing properties of p-Si/TiSiO4/Pt structure were investigated depending on concentration, temperature and interference gases. Electrical parameters with p type Si provided better results. The p-Si/TiSiO4/Pt sensor device showed Schottky behavior at low temperatures, but the device changed to ohmic behavior with increasing temperature.Öğe Hydrogen-Sensing Properties of Ultrathin Pt-Co Alloy Films(Mdpi, 2022) Erkovan, Mustafa; Deger, Caner; Cardoso, Susana; Kilinc, NecmettinThe present work aims to investigate the feasibility of utilizing Pt and PtCo alloy ultrathin films as hydrogen gas sensors in order to reduce the cost of the hydrogen gas sensors by using low-cost metallic materials. In this study, ultrathin Pt and PtCo alloy thin films are evaluated for hydrogen sensors. The stoichiometry and structural characterization of the thin films are observed from XPS, SEM, and EDX measurements. The 2-nm-thick Pt and PtCo films deposited by sputtering onto Si/SiO2 covers homogeneously the surface in an fcc crystalline plane (111). The hydrogen gas-sensing properties of the films are assessed from the resistance measurement between 25 degrees C and 150 degrees C temperature range, under atmospheres with hydrogen concentration ranging from 10 ppm to 5%. The hydrogen-sensing mechanism of ultrathin PtxCo1-x alloy films can be elucidated with the surface scattering phenomenon. PtCo thin alloy films show better response time than pure Pt thin films, but the alloy films show lower sensor response than pure Pt film's sensor response. Aside from these experimental investigations, first-principles calculations have also been carried out for bare Pt and Co, and also PtCo alloys. Compared to the theoretical calculations, the sensor response to change decreases with increasing Co content, a result that is compatible with the experimental results. In an attempt to explain the decrease in the sensor response of PtCo alloy films compared to bare Pt film, a variety of different phenomena are discussed, including the shrinking lattice of the structure or dendritic surface structure of PtCo alloy films by the increasing cobalt ratio.Öğe Palladium and platinum thin films for low-concentration resistive hydrogen sensor: a comparative study(Springer, 2021) Kilinc, NecmettinIn this study, palladium (Pd) and platinum (Pt) thin films are prepared via RF sputtering method with approximately 2 nm thicknesses on quartz substrates. Temperature-dependent resistances of Pd and Pt thin films are investigated at a temperature range from 30 to 130 degrees C. The results show that the resistance is directly proportional to temperature. The sensing properties of Pd and Pt thin films have been investigated depending on temperature and hydrogen concentration. It is found that Pt thin film shows higher sensitivity and lower limit of detection than Pd film, but the advantages of Pd thin film sensor are lower response time and unresponsive to the presence of oxygen compared to Pt thin film. The sensing mechanisms of Pd and Pt thin films are explained with continuous resistive H-2 sensor type and surface scattering phenomenon, respectively. The response and recovery times of the films are decreased with rising H-2 concentration and temperature.Öğe Perovskite based hydrogen detection and electrical properties of n-Si/ BaTiO3 heterojunction(Pergamon-Elsevier Science Ltd, 2026) Tasyurek, Lutfi Bilal; Karakurt, Huseyin; Kilinc, NecmettinIn this study, the electrical characterization of a heterojunction structure produced by coating powdered BaTiO3 from the perovskite family onto n-type silicon using the drop casting method was investigated at room temperature and as a function of temperature in a hydrogen atmosphere. The structural and optical characterization were evaluated using XRD analysis of the BaTiO3 powder, SEM - TEM images of the thin film structure, EDX spectrum, and UV analysis. The temperature-dependent current-voltage and alternating current changes of the nSi/BaTiO3 heterojunction were measured in a dry air atmosphere. According to the measurement results, the nSi/BaTiO3/Pt heterojunction device exhibited Schottky behavior. Furthermore, the sensor response of the heterojunction to hydrogen gas was calculated as 6.73. The hydrogen sensor response, measured at 50 degrees C at concentrations ranging from 500 ppm to 3%, increased in a concentration-dependent manner. Hydrogen detection measured at 100 degrees C shows a very good repeatability and stability at 20-min intervals in a 1% hydrogen atmosphere. The sensor response of n-Si/BaTiO3 heterojunction is about 3.71 +/- 4% in average for 70 days exposure to 1% hydrogen at 100 degrees C. Hydrogen gas tests were measured as a function of temperature and concentration changes. The obtained results are promising for the evaluation of the n-Si/BaTiO3 heterojunction as a hydrogen gas sensor.Öğe Platinum-Nickel alloy thin films for low concentration hydrogen sensor application(Elsevier Science Sa, 2022) Kilinc, Necmettin; Sanduvac, Senem; Erkovan, MustafaHydrogen (H-2) gas sensing properties of platinum (Pt) -nickel (Ni) alloy thin films deposited on a glass substrate by sputter technique are investigated depending on alloy composition, temperature and H-2 concentration. The structural properties of Pt-Ni alloy thin films are characterized by XRD, SEM and EDS techniques. The amount of Ni atom in the alloy thin films is increased from 0% up to 60% and the H-2 sensing properties of the alloy thin film sensors are examined in the concentration range of 25-1000 ppm H-2. The results revealed that the H-2 sensing mechanism of the same thickness pure Pt and Pt-Ni alloy thin films could be explained with surface scattering phenomenon, and the Pt-79-Ni-21 alloy thin film exhibited the best sensing performance to H-2 at all measured temperature ranges. The limit of detection for Pt and Pt-Ni alloy thin films is calculated as lower than 1 ppm, and the response times of the films are decreased with rising H-2 concentration and temperature. (C) 2021 Elsevier B.V. All rights reserved.Öğe Rare Earth Material for Hydrogen Gas Sensing: PtGd Alloy Thin Films as a Promising Frontier(Mdpi, 2024) Kilinc, Necmettin; Cardoso, Susana; Erkovan, MustafaAt the focus of our investigation lies the precision fabrication of ultrathin platinum-gadolinium (PtGd) alloy films, with the aim to use these films for resistive hydrogen gas sensing. The imperative for sensitive and selective sensors to harness hydrogen's potential as an alternative energy source drives our work. Applying rare earth materials, we enhance the capabilities of hydrogen gas sensing applications. Our study pioneers PtGd alloy thin films for hydrogen gas sensing, addressing a gap in existing literature. Here, we demonstrate the functional characteristics of 2 nm thick PtxGd100 ' x (x = 25, 50 and 75) alloy films, analyzing their hydrogen gas sensing properties, comprehensively examining the interplay between alloy composition, temperature fluctuation and hydrogen concentration. The effect of composition and structural properties on the sensing response were assessed using EDX and XPS. The films are tested at a temperature range between 25 degrees C and 150 degrees C with hydrogen gas concentrations ranging from 10 ppm to 5%. Hydrogen gas sensing mechanisms in PtGd alloy ultrathin films are explained by surface scattering. The unique combination of Pt and Gd offers promising characteristics for gas sensing applications, including high reactivity with hydrogen gas and tunable sensitivity based on the alloy composition.Öğe Surface-Engineered TiO2 Film for Enhanced Electrochemical Biosensing and Cell Monitoring(Wiley-V C H Verlag Gmbh, 2026) Sanli, Serdar; Tabak, Eray; Kilinc, Necmettin; Kosemen, Arif; Erginer, Merve; Ozturk, Sadullah; Barlas, Firat BarisIn vitro cell density measuring studies are mostly based on colorimetric methods; however, these approaches are limited to endpoint measurements rather than continuous data. To obtain more sensitive and continuous data, real-time monitoring of cell density is essential, which requires the development of surfaces with optimal physicochemical properties. TiO2 nanoporous structures are promising due to their favorable electrical properties, simple synthesis, unique porosity, biocompatibility, and stability. This study examined TiO2 films deposited onto titanium plates and screen-printed electrodes, characterized by scanning electron microscopy (SEM) and electrochemical techniques. HeLa and A549 cell proliferation on TiO2 was assessed and compared to polystyrene. Cell adhesion was evaluated via DAPI staining, fluorescence microscopy, and SEM. Electrochemical analyses (CV and EIS) were conducted on TiO2-coated electrodes. Results showed comparable proliferation on TiO2 and polystyrene, with effective adhesion confirmed by SEM. Electrochemical data demonstrated high sensitivity in detecting cellular differences, with detection limits of 150 cells for A549 and 107 for HeLa. These findings highlight TiO2 nanoporous structures as promising candidates for cell-based biosensor platforms.Öğe Synthesis and analysis of TiO2 nanotubes by electrochemical anodization and machine learning method for hydrogen sensors(Elsevier, 2022) Isik, Esme; Tasyurek, Lutfi Bilal; Isik, Ibrahim; Kilinc, NecmettinThe conductometric hydrogen gas sensors were used to explore TiO2 nanotubes in this study. TiO2 nanotubes are synthesized by anodization of the titanium foils using a neutral 0.5% and 1% (wt) NH4F in glycerol solution depending on anodization time and anodization voltage at the temperature of 20 degrees C. The amorphous, rutile and anatase phases of TiO2 are observed for as-prepared TiO2 nanotubes, annealed at 700 and 300 degrees C, respectively. The diameters of the nanotubes grow as the anodization time and voltage increase, according to scanning electron microscopy (SEM) images. The inner diameter of nanotubes is changed between similar to 70 nm to similar to 225 nm. Hydrogen sensing properties of Ti/TiO2 nanotubes/Pd device has been tested at room temperature under concertation range from 0.5% to 10% depending on the crystalline phase. The highest sensor response is observed for anatase crystalline TiO2 nanotubes. Typical Schottky-type behavior is observed from the I-V measurement. All the fabricated nanotube diameters are also simulated by using Support Vector Machine and Artificial Neural Network models. And also, some of the nanotube diameters which are not obtained experimentally (anodization voltage of 70 V) are estimated using the Support Vector Machine and Artificial Neural Network models. In addition, an analytical model is also proposed using Jacobi numeric analysis method alternative to the simulation model for the nanotube diameter. Finally, the analytical, simulation, and experimental results are compared, and the best result is obtained using the 1 Hidden Layer Artificial Neural Network model.Öğe Titanium nitride thin films grown by ion beam physical vapor deposition(Aip Publishing, 2025) Isik, Esme; Sterland, Dominic; Kilinc, Necmettin; Bell, Gavin R.A novel ion beam physical vapor deposition technique has been developed for TiN thin film deposition. The method uses only standard surface science tools, namely a cold cathode ion gun (normally used for sputter cleaning with Ar) operated with N2 gas and a modified titanium sublimation pump as a Ti PVD source. TiN thin films were deposited onto semi-insulating GaAs (001) substrates, and their physical and electrical properties were measured. X-ray photoelectron spectroscopy suggested predominantly TiN bonding with some oxynitride components. The DC conductivity increased in the range of 200-350 S/cm at temperatures ranging from 300 to 430 K. The behavior was consistent with the correlated barrier hopping model with an activation energy of 0.043 eV. The AC measurements (40 Hz to 0.2 MHz) indicated lower impedance above 10 kHz, possibly from the reduced effect of polarization at grain boundaries and other extended defects. The DC temperature dependence was also maintained even at the highest frequencies. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).
