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Subject: search.filters.subject.Microwave dielectric properties

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    Crystal structure, microwave dielectric properties and antenna simulation of low-permittivity Eu2CaMGa4O12(M = Ti, Sn, Zr) garnets
    (2025-12-01)
    Yang, Yang
    ;
    Wang, Zhaohui
    ;
    Qiu, Huizi
    ;
    Fang, Weishuang
    ;
    Tang, Ying
    The rattling of cations plays a vital role in energy loss mechanisms and is a fundamental approach for tuning dielectric performance. In this work, phase-pure garnets with the general formula Eu<inf>2</inf>CaMGa<inf>4</inf>O<inf>12</inf> (M = Ti, Sn, Zr) were successfully synthesized. The Eu<inf>2</inf>CaZrGa<inf>4</inf>O<inf>12</inf>, Eu<inf>2</inf>CaSnGa<inf>4</inf>O<inf>12</inf>, and Eu<inf>2</inf>CaTiGa<inf>4</inf>O<inf>12</inf> ceramics were obtained through sintering at 1400°C–1500°C for 6 h. The ceramics sintered at 1450°C exhibited favorable microwave dielectric performance with low ε<inf>r</inf> values of 10.74 (for Sn), 12.34 (for Zr) and 13.66 (for Ti), high Q×f values of 83,500 GHz (for Sn), 72,800 GHz (for Zr) and 59,200 GHz (for Ti), as well as negative τ<inf>f</inf> values of −60.60 ppm/°C (for Sn), −57.20 ppm/°C (for Zr) and −48.20 ppm/°C (for Ti). In Eu<inf>2</inf>CaMGa<inf>4</inf>O<inf>12</inf> (M = Ti, Sn, Zr) ceramics, the “rattling” effect of Eu<sup>3+</sup>and Ga<sup>3+</sup>dominated a slight overall structural expansion, which, in turn, led to the higher ε<inf>r</inf> compared to the theoretical prediction (ε<inf>r(C-M)</inf>) and contributed to the negative τ<inf>f</inf>. The variation in the Q × f values of the ceramics exhibited a negative correlation with the FWHM of the A<inf>1g</inf> Raman mode. Furthermore, due to the ultra-low loss of Eu<inf>2</inf>CaSnGa<inf>4</inf>O<inf>12</inf> ceramic, a dielectric resonator antenna was designed. This demonstrates the promising potential of the ceramics for 5G communication applications.
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    High-entropy gallium-based garnet microwave dielectric ceramics with low loss for C-band dielectric resonator antenna application
    (2025-11-01)
    Wen, Xinyang
    ;
    Xiang, Huaicheng
    ;
    Gu, Xiaolong
    ;
    Pulphol, Phieraya
    ;
    Vittayakorn, Naratip
    In this work, (Y<inf>0.5</inf> Nd<inf>0.5</inf> Sm<inf>0.5</inf> Eu<inf>0.5</inf> Ho<inf>0.5</inf> Yb<inf>0.5</inf> )Ga<inf>5</inf> O<inf>12</inf> high-entropy ceramic with a cubic garnet structure was designed and synthesized via a solid-state reaction method. Through the high-entropy regulation of the oxygen dodecahedron, the bond strength increases, the cation's bond valence approaches the ideal value, and the structural stability improves, thereby promoting the Q × f value. Low dielectric loss (Q × f = 130,100 GHz) was obtained in the high-entropy ceramic (Y<inf>0.5</inf> Nd<inf>0.5</inf> Sm<inf>0.5</inf> Eu<inf>0.5</inf> Ho<inf>0.5</inf> Yb<inf>0.5</inf> )Ga<inf>5</inf> O<inf>12</inf> , which exhibited a low relative permittivity (ε<inf>r</inf> ) of 12.36, a negative temperature coefficient of resonant frequency (τ<inf>f</inf> ) of −66.37 ppm/°C, and a high flexural strength of 229.68 MPa. Furthermore, a cylindrical dielectric resonator antenna (CDRA) was designed featuring high radiation efficiency (>90 %) and stable gain (5.91–5.97 dBi) within a 255 MHz bandwidth, showing promising application prospects in the C-band. This work indicates that the high-entropy strategy is feasible for the design of high-performance microwave dielectric ceramics.
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    Structural and microwave dielectric properties of temperature-stable Ca1-xEuxMo1-xNbxO4 ceramics for dielectric resonator antenna applications
    (2025-10-15)
    Gu, Xiaolong
    ;
    Tang, Ying
    ;
    Wu, Jiangtao
    ;
    Zhang, Ning
    ;
    Zhang, Siying
    Ca<inf>1-x</inf>Eu<inf>x</inf>Mo<inf>1-x</inf>Nb<inf>x</inf>O<inf>4</inf> (0.1 ≤ x ≤ 0.7) ceramics were synthesized through the co-substitution of Ca<sup>2+</sup> and Mo<sup>6+</sup> in CaMoO<inf>4</inf> using Eu<sup>3+</sup> and Nb<sup>5+</sup>. All samples exhibited tetragonal scheelite structures within the range of 0.1 ≤ x ≤ 0.6. However, at x = 0.7, a monoclinic fergusonite structure was observed, as the [Nb/MoO<inf>4</inf>] tetrahedron at the B-site transforms into a [Nb/MoO<inf>6</inf>] octahedron. As the substitution amount increases, ε<inf>r</inf> (11.39–16.40), Q×f (21,950–82,930 GHz), and τ<inf>f</inf> (−47.72 to +8.01 ppm/℃) all show a gradual increase. Notably, the τ<inf>f</inf> value of this system can shift from negative to positive. The structural influence mechanism on the microwave dielectric properties in Ca<inf>1-x</inf>Eu<inf>x</inf>Mo<inf>1-x</inf>Nb<inf>x</inf>O<inf>4</inf> ceramics was clarified through various analytical methods, including ion polarizability, P-V-L chemical bond theory, bond valence theory, density of states (DOS), and electron localization function (ELF). Additionally, a resonant antenna designed and simulated using Ca<inf>0.4</inf>Eu<inf>0.6</inf>Mo<inf>0.4</inf>Nb<inf>0.6</inf>O<inf>4</inf> meets the requirements for satellite communication.