Low-Loss Microwave Dielectrics in the Spinel-Structured (Mg1−xNix)Al2O4 Solid Solutions
Solid solutions of (Mg1−xNix)Al2O4 (x=0–1) have been prepared using the solid-state reaction method and their dielectric properties were measured at microwave frequencies. Formation of single-phase spinel-structured solid solutions was confirmed by X-ray diffraction analysis throughout the entire compositional range, and the measured lattice parameters varied linearly from 8.0810 Å at x=0 (MgAl2O4) to 8.0445 Å at x=1 (NiAl2O4) leading to a linear decrease in the unit cell volume from 527.71 to 520.59 Å3. The ionic polarizability obtained, however, increased with the increase of x to a maximum at x=0.25 and decreased thereafter. It shows only a small variance in the r with Ni substitution for Mg and a maximum r of 8.21 was achieved for (Mg0.75Ni0.25)Al2O4 in response to the highest ionic polarizability and relative density. However, the Q×f value can be significantly promoted up to a maximum value of 130 000 GHz (measured at 15.4 GHz) at x=0.25. In addition, substitution of Mg by Ni also helps to decline the f value from −65 ppm/°C at x=0 to −53.5 ppm/°C at x=0.25.
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Document Type: Research Article
Affiliations: Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Publication date: 01 July 2010