The practical application of CaSmAlO 4 microwave dielectric ceramics is limited by its low quality factor ( Q × f ) value and non-zero temperature coefficient resonant frequency ( τ f ) value. In this study, we introduced Mg 2+ –Ti 4+ ionic pairs into CaSmAlO 4 , along with an excess of 9% Sm 2 O 3 . The Mg 2+ –Ti 4+ ionic pairs substituted Al 3+ , and two phases simultaneously coexisted in the ceramics: CaSmAlO 4 and Sm 2 O 3 . As the doping concentration of Mg 2+ –Ti 4+ ionic pairs increased, the relative permittivity exhibited an upward trend, while the quality factor and resonant frequency temperature coefficient first rose and then descended. Remarkably, 0.09Sm 2 O 3 –0.91CaSmAl 0.7 Mg 0.15 –Ti 0.15 O 4 sintered at 1450 °C yielded excellent dielectric properties: ε r = 19.72, Q × f = 72,936 GHz, and τ f = –0.044 ppm·°C − 1 . The factors influencing the microwave dielectric properties of 0.09Sm 2 O 3 –0.91CaSmAlO 4 ceramics were further examined by considering the crystal structure, grain size, Lichtenecker logarithmic rule, tolerance factor and packing fraction. Graphic abstract
Ca 1.15 Sm 0.85 Al 0.85 Ti 0.15 O 4 ceramics with different ball milling temperatures were prepared by the solid-phase method. The X-ray diffraction results showed that the high ball milling temperature (45 ± 5 °C) led to the hydration of the material phase, resulting in the formation of a large amount of (CaO) 3 Al 2 O 3 (H 2 O) 6 phase. The results of the scanning electronic microscope and the energy dispersive spectroscopy confirmed that the hydrated powders resulted in heterogeneous microstructure characteristics with a wide grain size distribution of ceramics sintered, which degraded dielectric characteristics, especially reducing the quality factor (around 30,000). However, controlling the ball mill temperature in the range of 20 ± 5 °C, there was no hydration occurring in the slurry. Thus, the sintered ceramics at optimum temperature exhibited excellent microwave dielectric properties, a dielectric constant of around 19.6, a high-quality factor of 70,000 GHz, and a near zero temperature coefficient (< ± 4 ppm/°C) of resonant frequency in a wide temperature range from − 40 to 125 °C.
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