Anomalous large positive τf of two K20 microwave dielectric ceramics LaMGa11O19 (M = Mg, Zn) as temperature compensators

In this work, two novel hexagonal magnetoplumbite-type LaMGa 11 O 19 (M = Mg, Zn) ceramics were prepared and deeply investigated. XRD patterns, SAED and HRTEM images analysis results demonstrated that the LaMGa 11 O 19 (M = Mg, Zn) ceramics are formation of hexagonal magnetoplumbite structure with a space group of P 6 3 / mmc . Both ceramics exhibited relatively high density (>95 %) and large positive τ f (+145.1 and + 136.7 ppm/°C), combined with moderate ε r around 20 and reasonable Q  ×  f values of 19,328 GHz and 22,197 GHz, which be used as a temperature compensator for LTCC applications. The intense rattling effect of La 3+ cations resulted in abnormally high dielectric constant with a large positive variation by a factor of over 0.70 from the theoretical values calculated using the Clausius-Mossotti formula according to each ion's polarizability, negative τ αm , and positive τ f values. The P–V–L chemical bond theory analysis and impedance spectroscopy showed that the large dielectric loss might result from the high ionicity of the La-O bond and conduction loss, thus leading to relatively low Q  ×  f for the LaMGa 11 O 19 (M = Mg, Zn) ceramics.