Phase Structure, Bond Features, and Microwave Dielectric Characteristics of Ruddlesden–Popper Type Sr2TiO4 Ceramics

This work studied the phase constitution, bond characteristics, and microwave dielectric performances of Sr₂TiO₄ ceramics. Based on XRD and Rietveld refinement analysis, pure tetragonal Ruddlesden-Popper type Sr₂TiO₄ ceramic is synthesized at 1425~1525 °C. Meanwhile, the microstructure is dense and without porosity, indicating its high sinterability and densification. Great microwave dielectric performances can be obtained, namely an ε_r value of 39.41, and a Q × f value of 93,120 GHz, when sintered at 1475 °C. Under ideal sintering conditions, the extrinsic factors are minimized and can be ignored. Thus, the intrinsic factors are considered crucial in determining microwave dielectric performances. Based on the P-V-L complex chemical bond theory calculation, the largest bond ionicity, and proportions to the bond susceptibility from Sr-O bonds suggest that Sr-O bonds mainly determine the dielectric polarizability. However, the Ti-O bonds show lattice energy about three times larger than Sr-O bonds, emphasizing that the structural stability of Sr₂TiO₄ ceramics is dominated by Ti-O bonds, and the Ti-O bonds are vital in determining the intrinsic dielectric loss. The thermal expansion coefficient value of the Sr₂TiO₄ structure is also mainly decided by Ti-O bonds.