Yazar "Demir, Ahmet" seçeneğine göre listele

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    A novel lanthanum hexaboride-modified cementitious composites: evolution and microstructural architecture of LaB6-integrated GFRC systems with enhanced dielectric response
    (Elsevier Ltd, 2026) Demir, Ahmet; Subaşı, Serkan; Dehgan, Haydar; Ramazanoğlu, Doğu; Maraşlı, Muhammed; Aksu, Mecit; Gencel, Osman; Musatat, Ahmad Badreddin; Subaşı, Azime
    This study investigates the integration of lanthanum hexaboride (LaB6) microparticles into glass fiber-reinforced concrete (GFRC) to improve its dielectric and microstructural properties. GFRC mixtures with 1–3 % LaB6 replacement were characterized for capacitance, impedance, dielectric constant (ε′ and ε″), dissipation factor (tanδ), electrical modulus (M′ and M″), and Cole-Cole diagrams across varying frequencies (20 Hz–5 MHz) and hydration times (7–58 days). Comprehensive Microstructural, Thermal Stability, and Chemical Characterization analyses were also performed. Results demonstrate that LaB6 significantly improves GFRC's capacitance, conductivity, and dielectric properties. Specifically, L2 and L3 samples exhibited capacitance values approximately 100 times higher than the reference and L1 samples after 56 days, and approximately 25 times greater capacitance behavior across the tested frequency spectrum. The real dielectric constant (ε′) reached 250-fold, decreasing by about 10 times with LaB6 addition in L2 and L3, indicating improved insulation. Dielectric losses (ε″) were also markedly higher for L2 and L3, approaching 100 times greater than R and L1, implying favorable conductive functionality. Cole-Cole analysis indicated minimal dielectric dispersion for L2 and L3, suggesting near-ideal polarizable interfaces. Equivalent circuits were fitted, demonstrating that LaB6 significantly influences the electrical transport and storage mechanisms within the GFRC composites, leading to improved dielectric performance. Scanning electron microscopy (SEM) revealed denser microstructures, while thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy (FTIR) corroborated enhanced thermal stability, bond strength, and favorable microstructural interactions. These findings highlight LaB6 as a promising additive for developing high-performance cementitious composites with tailored electrical responses for smart concrete applications.
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    Dielectric property enhancement of glass fiber-reinforced concrete via TiO₂ nanocomposites
    (Elsevier Ltd, 2025) Ramazanoğlu, Doğu; Subaşı, Azime; Musatat, Ahmad Badreddin; Demir, Ahmet; Subaşı, Serkan; Maraşlı, Muhammed
    This study addresses the critical gap in traditional glass fiber-reinforced concrete (GFRC), which lacks tailored electrical properties for modern energy-related applications. We introduce a novel approach by incorporating a TiO₂-based hybrid composite (TiO₂-@) into GFRC to develop multifunctional composites with enhanced dielectric, mechanical, and energy storage capabilities. Experimental results demonstrate that TiO₂-@ doping at 2 % concentration achieves the most significant improvements: a dielectric constant increase to ∼420 at 100 Hz (compared to ∼180 for undoped GFRC), capacitance enhancement to 71 pF at 100 Hz (versus 18 pF in the reference), and AC conductivity elevation by 205 % after aging. The 2 % TiO₂-@ sample also exhibited a Leeb hardness increase to 486 HLD (from 159 HLD pre-aging), highlighting its structural robustness. Frequency-dependent analyses revealed modified polarization mechanisms and charge transport dynamics, with Cole-Cole plots and impedance spectroscopy confirming reduced capacitive reactance and enhanced interfacial interactions. These results establish TiO₂-@ as a transformative additive for GFRC, bridging the gap between structural performance and energy functionality. The work pioneers the integration of TiO₂ nanocomposites into cementitious matrices, offering a dual-purpose material for smart construction systems and embedded energy storage devices.
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    Electrical and dielectric tailoring of glass fiber-reinforced concrete using ZnO-based hybrid nanocomposites
    (Springer, 2026) Ramazanoğlu, Doğu; Musatat, Ahmad Badreddin; Subaşı, Azime; Demir, Ahmet; Subaşı, Serkan; Maraşlı, Muhammed
    This study investigates frequency-dependent dielectric and electrical transport properties of glass fiber-reinforced concrete (GFRC) systematically doped with ZnO-based hybrid composite (ZnO-@) nanoparticles at 1%, 2%, and 3% mass fractions. Electrical impedance spectroscopy (20 Hz-5 MHz) coupled with microstructural characterization (SEM-EDX, FTIR) and mechanical validation establishes concentration-dependent polarization mechanisms governing electromagnetic property modulation. The 2% ZnO-@ formulation exhibits optimal dielectric enhancement with maximum real permittivity (epsilon '), superior AC conductivity (100 Hz-10 kHz domain), and 100% imaginary modulus augmentation (M ''), attributed to Maxwell-Wagner-Sillars interfacial polarization at ZnO-cement matrix boundaries. Equivalent circuit modeling reveals that grain boundary resistance escalates to 5.8 M Omega at optimal doping, and constant phase element (CPE) exponent values (P = 0.77-0.84) confirming non-Debye relaxation due to hierarchical microstructural heterogeneity. The critical percolation threshold, between 2% and 3% ZnO concentration, demarcates the transition from capacitive to conductive behavior, where specimens at 3% exhibit dielectric parameter regression toward baseline values due to nanoparticle agglomeration and the formation of conductive pathways. Spectroscopic validation confirms the integration of wurtzite-phase ZnO (Zn-O: 474 cm(-)1) with preserved calcium silicate hydrate phases, while post-aging Leeb hardness measurements demonstrate 171-176% mechanical reinforcement (387-456 HLD), validating the retention of structural durability. These findings establish quantitative compositional guidelines for engineering multifunctional construction composites with tailored electromagnetic response characteristics for interference shielding, capacitive energy storage, and electromagnetically compatible innovative infrastructure applications.
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    Investigating ultra-thin rGO coated ZnO core-shell structures in MOS devices: electrical/dielectric characteristics and relaxation mechanism
    (Elsevier Ltd, 2024) Kırkbınar, Mine; İbrahimoğlu, Erhan; Demir, Ahmet; Çalışkan, Fatih
    The study focused on the relaxation and polarisation mechanisms of Al/(rGO:ZnO core-shell)/pSi/Al MOS structures. For this purpose, the rGO:ZnO core-shell structures were synthesised by sol-gel procedures and coated on pSi by spin-coating. The structures were characterized as chemical, morphological and micro-structural using FESEM-EDS, AFM, XRD and Raman analysis. Additionally, the capacitance (C), conductance (G/omega), dielectric permittivity (epsilon ' and epsilon ''), loss factor(tan delta), electric modulus(M ' and M '') of the samples were successfully examined by DS over the wide range of frequencies (100 Hz-1 MHz) for determining dielectric parameters. Three distinct regions were visible on the C-V and C-omega plots: accumulation (-4 to 0 V), depletion (0 to 2 V), and inversion (2 to 4 V). Two relaxation times (10(-4)s-10(-7)s) were obtained in epsilon '-V and epsilon '-omega graphs between 1-100 kHz (region 1) and 100 kHz-1 MHz (region 2). The relaxation times were according to the Maxwell-Wagner and dipolar polarisation mechanism. As a result, the capacitive effect was observed and the equivalent RC circuit obtained from the Cole-Cole diagrams allowed the samples to be used in energy storage or different electronic applications.
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    Multifunctional GFRC composites: PEDOT: PSS-driven dielectric enhancement for energy storage and sensing applications
    (Elsevier Ltd, 2026) Demir, Ahmet; Musatat, Ahmad Badreddin; Subaşı, Azime; Ramazanoğlu, Doğu; Dehgan, Haydar; Maraşlı, Muhammed; Gencel, Osman; Subaşı, Serkan
    This study presents a comprehensive investigation into the development and characterization of multifunctional Glass Fiber Reinforced Cement (GFRC) composites enhanced with Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT: PSS) to impart advanced electrical properties. We systematically analyzed the influence of PEDOT: PSS concentration (0–15 wt %) and curing age on the dielectric behavior of these novel composites, evaluating their capacitance, dielectric constant, loss factor, and electrical modulus across a broad frequency range (10 Hz-10 MHz). The integration of PEDOT: PSS significantly modified the material's electrical characteristics, demonstrating concentration-dependent variations and complex relaxation mechanisms dominated by Maxwell-Wagner interfacial polarization. The optimized P2 formulation (10 wt % PEDOT: PSS) exhibited superior electrochemical performance, maintaining the highest capacitance values and achieving a peak dissipation factor (tan δ) of 0.43 ± 0.02 at day 15, representing a 185 % enhancement over unmodified GFRC. EDX analysis confirmed successful polymer incorporation, with P2 exhibiting the highest carbon content (5.8 wt %) and sulfur content (1.8 wt %), indicating optimal dispersion. Equivalent circuit models were established and validated (R2 > 0.98), providing insights into complex charge transport mechanisms within this hybrid material. Microstructural analyses via scanning electron microscopy revealed significant morphological modifications, including the formation of crystalline and plate-like structures, while complementary FT-IR and TGA analyses confirmed polymer-cement interaction stability and thermal stability up to 450 °C. These findings establish fundamental design principles for creating electrically conductive cementitious materials with tunable dielectric properties, enabling strategic deployment in innovative infrastructure systems, energy storage devices, and electromagnetic shielding technologies.
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    Multifunctional SnO2-@ doped glass fiber-reinforced concrete: improved microstructure, mechanical, dielectric, and energy storage characteristics
    (Elsevier Ltd, 2025) Ramazanoğlu, Doğu; Subaşı, Azime; Musatat, Ahmad Badreddin; Demir, Ahmet; Subaşı, Serkan; Maraşlı, Muhammed
    This study explores SnO₂-based hybrid composite (SnO₂-@) doped glass fiber-reinforced concrete (GFRC) for enhanced dielectric, energy storage, and mechanical performance. Microstructural analysis confirmed SnO₂-@ promotes ettringite and calcium silicate hydrate (C-S-H) formation, improving matrix integrity. Aged samples exhibited a 650 % increase in surface roughness (Ra) and over 200 % higher Leeb hardness, demonstrating durability. Dielectric spectroscopy revealed frequency-dependent tunability: 1 % SnO₂-@ achieved a peak dielectric constant (ε' = 130 at 10 kHz), shifting to ε' = 140 at 100 kHz for 2–3 % doping. AC conductivity surged by 60 %, correlating with SnO₂-@-induced interfacial polarization and charge mobility. Energy storage capacity improved significantly, attributed to optimized dipole alignment and reduced leakage currents. Color stability remained robust (ΔE* ≤ 2.8 post-aging), ensuring aesthetic viability. These results position SnO₂-@-doped GFRC as a multifunctional material for smart infrastructure, integrating structural resilience, adaptive dielectric properties, and energy storage potential for next-generation urban applications.