@article{Yang2024, 
author = {Yang Yang and Weishuang Fang and Huixing Lin and Jie Li and Huaicheng Xiang and Ying Tang and Lei Li and Liang Fang},
title = {SrGa12O19: The first low-εr Ga-based microwave dielectric ceramic with anomalous positive τf},
year = {2024},
journal = {Journal of Advanced Ceramics},
volume = {13},
number = {9},
pages = {1432-1441},
keywords = {microwave dielectric properties, magnetoplumbite, rattling effect, chemical bond theory},
url = {https://www.sciopen.com/article/10.26599/JAC.2024.9220947},
doi = {10.26599/JAC.2024.9220947},
abstract = {Dielectric ceramics with low permittivity (εr), high quality factor (Q×f), and near-zero resonant frequency (τf) in the microwave bands are key materials used in fifth/sixth-generation (5G/6G) telecommunication, whileτf of most low-εr microwave dielectric ceramics is relatively negative. In this work, the first low-εr Ga-based ceramic SrGa12O19 with an anomalous positive τf was reported, and the causes of the positive τf, intrinsic polarization, and loss mechanism were systematically studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the SrGa12O19 ceramic formed a pure hexagonal magnetoplumbite structure with spinel blocks and rock-salt blocks stacked along the crystallographic c-axis. When sintered at 1430 °C, it possessed the optimal microwave dielectric properties of a low εr of 14.46, high Q×f of 64,705 GHz, and exceptional positive τf of +55.7 ppm/°C, along with a low linear thermal expansion coefficient (αL) of 11.617 ppm/°C. The large positive deviation between εr and εr(C–M) of 45.31% resulted from the rattling effect of atoms in the rock-salt block. The unique positive τf (+55.7 ppm/°C) was governed by the rattling effect, resulting in a positive ταm (the temperature coefficient of ion polarizability) of 8.489 ppm/°C and a large negative temperature coefficient of permittivity (τε) of −132.864 ppm/°C. Phillips–Vechten–Levine (P–V–L) chemical bond theory revealed greater contributions of the spinel block to bond ionicity (fi, 52.95%), permittivity (ε, 55.15%), bond energy (E, 56.87%), and lattice energy (U, 74.88%) than those of the rock-salt block. The intrinsic dielectric properties were analyzed using infrared (IR) reflectivity spectra. The favorable performance of the SrGa12O19 ceramic indicated that it is a novel τf compensator. This selection of compounds with different structural layer combinations provides a new idea for exploring excellent microwave dielectric ceramics.}
}