Enhanced Microwave Dielectric Properties in Mg₂Al₄Si₅O₁₈ Through Cu²⁺ Substitution

Abstract

The Mg 2 Al 4 Si 5 O 18 ceramic is considered as a kind of important candidates for millimeter-wave applications. In this work, Mg 2x Cu x Al 4 Si 5 O 18 (0 � x � 0.16) ceramics were synthesized by solidstate reaction, aiming to improve the microwave dielectric properties. According to the X-ray powder diffraction (XRD) analysis, Cu 2 + ions enter into the Mg 2 Al 4 Si 5 O 18 lattice and form a solid solution. The dense microstructure was observed in the Cu-substituted Mg 2 Al 4 Si 5 O 18 ceramics at x = 0.04 sintered at 1420°C. The dielectric constant (ɛ r ) values depend on the microstructure, secondary phase and ionic polarizability of the samples. The quality factor (Qf) values are dominated by the microstructure, secondary phase and centro-symmetry of [Si 4 Al 2 ] hexagonal ring. The temperature coefficients of resonance frequency (τ f ) are strongly related to the Mg/CuÀ O bond valance. In comparison to pure Mg 2 Al 4 Si 5 O 18 ceramics, the excellent microwave dielectric properties with ɛ r = 4.56, Qf = 31,100 GHz and τ f = À 52 ppm/°C were obtained at x = 0.04 with sintering at 1420°C. Thus, the Mg 2-x Cu x Al 4 Si 5 O 18 (0 � x � 0.16) ceramics will be promising millimeter-wave communication materials.

Ultra‐high Quality Factor of (Zn2/3Nb1/3)3+ Co‐substitution MgAl2O4 Microwave Dielectric Ceramics

“…This finding agrees with those of previous studies that reported a positive correlation between the packing fraction and Qf values. [31,32,45] In contrast, there is no significant correlation between the change in covalence and Qf value, indicating that covalence is not the reason for the variation in the Qf value in this study. Furthermore, the high Zn 2þ and Nb 5þ ion contents significantly reduce the sintering temperature of the ceramics when x = 0.5.…”

Crystal structure and microwave dielectric properties of Li2(Mg1–xCux)2Mo3O12 ceramics sintered at ultra‐low temperature

“…The binding energies of the peaks of Mo 3d at 232 and 235.4 eV are consistent with the results of Figure 7E, indicating that Mo exists as Mo 6+ in the material 55 . Figure 7F shows the peak fitting curves for Cu 2p, the two fitted peaks at 932.7 and 954.2 eV correspond to Cu + 2p, while the two fitted peaks at 936.4 and 956.5 eV correspond to Cu 2+ 2p, which suggests the presence of both Cu + and Cu 2+ 30,56 . The formation of oxygen vacancies during high‐temperature sintering promotes the partial reduction of Cu 2+ with the following reactions (4) and (5) 57 : $$$$\begin{equation}{\mathrm{O}}_{\mathrm{o}}^ \times \leftrightharpoons \frac{1}{2}{{\mathrm{O}}}_2 + V_{\mathrm{O}}^{\cdot\cdot} + 2{\mathrm{e^{\prime}}}\end{equation}$$$$ $$$$\begin{equation}{\mathrm{Cu}}^{2 + } + {\mathrm{e^{\prime}}} \leftrightharpoons {\mathrm{Cu}}^ + ,\end{equation}$$$$where $${\mathrm{O}}_{\mathrm{o}}^ \times $$ represents O lattice sites, $$V_{\mathrm{O}}^{\cdot\cdot}$$ represents oxygen vacancies, and e′ represents free electrons.…”

“…55 Figure 7F shows the peak fitting curves for Cu 2p, the two fitted peaks at 932.7 and 954.2 eV correspond to Cu + 2p, while the two fitted peaks at 936.4 and 956.5 eV correspond to Cu 2+ 2p, which suggests the presence of both Cu + and Cu 2+ . 30,56 The formation of oxygen vacancies during high-temperature sintering promotes the partial reduction of Cu 2+ with the following reactions ( 4) and ( 5) 57 :…”

“…28,29 CuO has been introduced by replacing divalent metal ions with Cu 2+ to reduce the sintering temperature of ceramics. For example, substituting Mg 2+ with Cu 2+ reduces the sintering temperature of Mg 2 Al 4 Si 5 O 18 ceramics from 1600 • C to 1420 • C, 30 substituting Mg 2+ with Cu 2+ reduces the sintering temperature of MgTiO 3 ceramics from 1430 • C to 1150 • C, 31 and substituting Zn 2+ with Cu 2+ reduces the sintering temperature of Zn 2 WO 3 ceramics from 1200 • C to 925 • C. 32 Numerous studies have shown that the substitution of Cu 2+ ions for divalent metal ions reduces the sintering temperature of ceramics. In this study, Cu 2+ was used to replace Mg 2+ in Li 2 Mg 2 Mo 3 O 12 (considering the equal valence of Cu 2+ and Mg 2+ ions and similar ionic radii 33 ) to achieve the ultra-low temperature sintering of Li 2 Mg 2 Mo 3 O 12 , and the sintering characteristics, crystal structure, and microwave dielectric properties of Li 2 (Mg 1-x Cu x ) 2 Mo 3 O 12 (0 ≤ x ≤ 0.1) ceramics are systematically studied.…”

“…CuO has been introduced by replacing divalent metal ions with Cu 2+ to reduce the sintering temperature of ceramics. For example, substituting Mg 2+ with Cu 2+ reduces the sintering temperature of Mg 2 Al 4 Si 5 O 18 ceramics from 1600°C to 1420°C, 30 substituting Mg 2+ with Cu 2+ reduces the sintering temperature of MgTiO 3 ceramics from 1430°C to 1150°C, 31 and substituting Zn 2+ with Cu 2+ reduces the sintering temperature of Zn 2 WO 3 ceramics from 1200°C to 925°C 32 …”