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187 results on '"Taheri-Nassaj, Ehsan"'

29. Crystal Structure and Microwave Dielectric Property of xMgO-SiO2 (x = 1~2) System for 5G Applications

Author

Wang, Yan, primary, Li, Jiajing, additional, Zhu, Haipeng, additional, Wang, Qilei, additional, Sun, Tulai, additional, Ni, Tao, additional, Lin, Yanghong, additional, Liu, Yu, additional, Mao, Minmin, additional, Hu, Ji, additional, Liu, Bing, additional, Bafrooei, Hadi Barzegar, additional, Ma, Zhongyan, additional, Ren, Yingjie, additional, Shi, Feng, additional, Taheri-Nassaj, Ehsan, additional, Wang, Dawei, additional, and Song, Kaixin, additional

Published
2023
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38. Dielectric, pyroelectric, and ferroelectric studies in (1 − x)AgNbO3–xFeNbO4 lead-free ceramics.

Author

Moradi, Parastoo, Taheri-Nassaj, Ehsan, Yourdkhani, Amin, Mykhailovych, Vasyl, Diaconu, Andrei, and Rotaru, Aurelian

Subjects
*LEAD-free ceramics, *CERAMICS, *ORTHORHOMBIC crystal system, *PYROELECTRICITY, *FERROELECTRIC ceramics, *DIELECTRICS, *SPECIFIC gravity, *ENERGY density, *RAMAN spectroscopy
Abstract

In the present study, the effect of heterovalent Fe3+ ions on the dielectric, pyroelectric, and ferroelectric properties of the (1 − x)AgNbO3–xFeNbO4 (x = 0.005, 0.01, 0.025, 0.05, and 0.1) system was investigated. The substitution of smaller ionic radius Fe3+ in B-sites and the formation of FeNbO4 as a secondary phase contributed to improved dielectric performance, especially the pyroelectric effect, of (1 − x)AgNbO3–xFeNbO4 ceramics by generating electron-rich ceramics. The (1 − x)AgNbO3–xFeNbO4 ceramics were prepared by conventional solid-state sintering. Pure AgNbO3 had a perovskite crystal structure with an orthorhombic crystal system, but the FeNbO4 in (1 − x)AgNbO3–xFeNbO4 ceramics was formed as a secondary phase with a monoclinic structure. In addition, the XRD and Raman spectroscopy data showed that some Fe3+ was substituted into B-sites of AgNbO3. The introduction of FeNbO4 effectively reduced the average grain size from 1.85 ± 0.09 μm to 1.22 ± 0.03 μm for pure AgNbO3 and 0.9AgNbO3–0.1FeNbO4, respectively. In addition, the relative density of the (1 − x)AgNbO3–xFeNbO4 ceramics decreased from 97.96% ± 0.01 for x = 0 to 96.75% ± 0.03 for x = 0.1. The real part of the permittivity ε′, at room temperature, increased from 186.6 for x = 0 to a value of 738.7 for x = 0.1. Additionally, the maximum pyroelectric coefficient increased fivefold, reaching values of 2270 nC cm−2 K−1 for x = 0.1. Furthermore, a harvested pyroelectric energy density (W) of 1140 μJ cm−3 for x = 0.025 was achieved, which is appreciably higher than the 840 μJ cm−3 value for x = 0. [ABSTRACT FROM AUTHOR]

Published
2023
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44. Crystal Structure and Microwave Dielectric Property of x MgO-SiO 2 (x = 1~2) System for 5G Applications.

Author

Wang, Yan, Li, Jiajing, Zhu, Haipeng, Wang, Qilei, Sun, Tulai, Ni, Tao, Lin, Yanghong, Liu, Yu, Mao, Minmin, Hu, Ji, Liu, Bing, Bafrooei, Hadi Barzegar, Ma, Zhongyan, Ren, Yingjie, Shi, Feng, Taheri-Nassaj, Ehsan, Wang, Dawei, and Song, Kaixin

Subjects
DIELECTRIC properties, CRYSTAL structure, PARTICLE size distribution, MICROWAVES, 5G networks, X-ray spectra
Abstract

Mg2SiO4 and MgSiO3 ceramics with superior microwave dielectric properties are considered to be promising candidates for 5G applications. However, a slight deviation from the stoichiometric Mg/Si ratio will significantly influence their microwave dielectric properties, which will hinder their practical applications. In this work, the xMgO-SiO2 (x = 1~2) ceramics were synthesized by a solid-state reaction method. The influence of the Mg/Si ratio x on the crystalline phase, microstructure, and microwave dielectric properties was investigated through X-ray diffraction (XRD), a scanning electron microscope (SEM), and the resonant cavity method. The XRD patterns revealed the coexistence of Mg2SiO4 and MgSiO3 within the x range of 1~2, which was further demonstrated by the energy-dispersive X-ray spectra. The SEM images show a typical polycrystalline morphology of ceramics with an inhomogeneous grain size distribution. It is found that the microwave dielectric properties fluctuate at both sides of the x range while those remain relatively stable with minor changes at the intermediate components, indicating an obvious low composition dependence helpful for practical applications. Further, a demonstrator of a microstrip patch antenna for 5G applications using the 1.5MgO-SiO2 ceramic was designed and fabricated, and a return loss of −16.2 dB was demonstrated, which demonstrated the potential applications. [ABSTRACT FROM AUTHOR]

Published
2023
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45. Improvement of CO Oxidation and CH4Combustion by Pd and Pt Partial Substitution on LaMn0.5Cu0.5O3Perovskite

Author

Farhang, Yaghoub, Taheri-Nassaj, Ehsan, and Rezaei, Mehran

Abstract

LaMn0.5Cu0.5O3(LMC) as the parent perovskite and Pd- and Pt-doped LaMn0.5Cu0.5O3catalysts (LMCPd and LMCPt) instead of Cu were synthesized in a new solid-state synthesis technique at a low temperature. Perovskite lattice formation of the LMC catalyst was successfully performed at 600 °C. All perovskites were investigated by X-ray diffraction, HRTEM, O2-TPD, H2-TPR, BET, and XPS analyses. The prepared perovskites were used as heterogeneous catalysts for CO oxidation and methane combustion reactions. The catalytic performance of the LMC catalyst was noticeably enhanced via Pd and Pt substitution instead of Cu. The enhancement in the mobility of lattice oxygen and specific surface area has triggered this catalytic performance improvement, which play an important role in CO oxidation and methane combustion. The Mn 2p and Mn 3s XPS spectra showed that by doping Pd and Pt in the LMC perovskite, Mn was affected in different states and the Mn 3s peaks were only observed in the LMCPt catalyst. XPS spectra of the LMCPd1 sample showed a high oxidation state of Pd3+or Pd4+, from which it can be concluded that Pd was successfully incorporated into the LMC perovskite lattice. The H2-TPR profiles of the LMCPd and LMCPt perovskites revealed that the reduction peaks of Cu and Mn were shifted to lower temperatures by increasing Pd and Pt partial substitution due to the synergetic effect of the cation and the H2-spillover effect of palladium and platinum.

Published
2023
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49. Cold Sintering Isomagnetic Dielectric NaCl-Nickel Zinc Ferrite Composite Ceramics.

Author

Han, Jiuyuan, Chi, Mengjiao, Yang, Liu, Liu, Bing, Mao, Minmin, Bafrooei, Hadi Barzegar, Ma, Zhongyan, Ren, Yingjie, Shi, Feng, Taheri-Nassaj, Ehsan, Wang, Dawei, and Song, Kaixin

Subjects
NICKEL ferrite, ZINC ferrites, SINTERING, PERMITTIVITY, MAGNETIC flux leakage, SPECIFIC gravity, DIELECTRIC loss
Abstract

In this study, dense composites of xNaCl-(1−x)Ni0.5Zn0.5Fe2O4 (referred to as NaCl-NZO) and xH3BO3-(0.8−x)Ni0.5Zn0.5Fe2O4-0.2NaCl (referred to as HB-NZO-NaCl) were prepared using the cold sintering process. The objective was to investigate the cold sintering procedure for fabricating ferrite composite ceramics with comparable permeability and dielectric constants suitable for radio-frequency electronic device applications. Optimal cold sintering conditions were determined as 200 °C/30 min/500 MPa with a relative density of 95% for NaCl-NZO and 120 °C/30 min/300 MPa with a relative density of 95.4% for HB-NZO-NaCl. X-ray diffraction and scanning electron microscope analyses confirmed the absence of secondary phases. The resulting composite ceramics showed promising characteristics, with the 0.5NaCl-0.5NZO composition exhibiting a dielectric constant of 6.2 @ 100 MHz, dielectric loss of 0.02 @ 100 MHz, permeability of 2.5 @ 100 MHz, and magnetic loss of 0.001 @ 100 MHz. Similarly, the 0.3HB-0.5NZO-0.2NaCl composition displayed a dielectric constant of 5.9 @ 100 MHz, dielectric loss of 0.02 @ 100 MHz, permeability of 5.1 @ 100 MHz, and magnetic loss of 5 × 10−4 @ 100 MHz. These findings indicate potential applications in wireless communication. [ABSTRACT FROM AUTHOR]

Published
2023
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