Infrared Reflectivity Spectra and Microwave Dielectric Properties of (Sr _{1− x} Ca _x )SmAlO ₄ (0≤ x ≤1) Ceramics

Dense (Sr _{1− x} Ca _x )SmAlO ₄ (0≤ x ≤1) ceramics with K ₂ NiF ₄ ‐type tetragonal structure in I 4/ mmm space group were prepared by a standard solid‐state reaction. The crystal structures and microstructures were characterized by X‐ray diffraction and scanning electron microscopy, and the infrared reflectivity spectra were measured and analyzed by classical oscillator model simulation. The data were extrapolated below the measured frequency range to estimate the intrinsic dielectric constant and dielectric loss. A greatly improved Q × f value is obtained in the present ceramics, which is attributed to both the intrinsic and extrinsic features. The decreased intrinsic dielectric loss can be interpreted as the competing results of the decreased radius difference of A‐site ions and the decreased tolerance factor. On the other hand, the extrinsic dielectric loss is also suppressed by the uniform microstructure and the large grain size in the solid solutions. The measured dielectric constant ɛ _r remains 18–19, which is slightly lower than the calculated one. The τ _f value decreases monotonously from −2.0 to −10.8 ppm/°C as x increases, which is primarily dominated by the thermal expansion coefficient.