Effects of CaO-B₂O₃ glass addition on the low-temperature sintering and cation ordering in Sr_xLa_(1-x)Ti_xAl_(1-x)O₃ ceramics

Sr_xLa_(1-x)Ti_xAl_(1-x)O₃ (SLTA, x = 0.4-0.7) ceramics with additive of CaO-B₂O₃ glass (1-10 wt%) were prepared by a solid-state reaction process, which led to a significant decrease in sintering temperature, from 1550 °C to 1100 °C. Dielectric properties of ceramics at low frequency were significantly improved by CaO-B₂O₃ glass addition, especially the obtained dielectric loss ∼6 × 10^-4 at room temperature and 1 MHz. Superlattice reflection was detected in the prepared oxides by X-ray diffraction (XRD), selected area electron diffraction (SAED) and Raman spectra, indicating presence of cation ordering. Meanwhile, lattice images of high-resolution transmission electron microscopy (HRTEM) also certificated the presence of cations ordering. Notably, the detected superlattice reflection in perovskite structure associated with antiparallel A-site cation displacements and anti-phase octahedral tilting. This ordered structure as well as low temperature sintering both affected the microwave dielectric properties of Sr_0.7La_0.3Ti_0.7Al_0.3O₃ ceramics, which exhibited with ε_r ∼ 43.3, Q × f ∼ 10,780 GHz and τ_f ∼ 20.8 ppm/°C. The smaller cations doped in A site, a larger difference in ionic radius or cation valence of B-site cations were considered to primarily facilitate the formation of cation ordering, which promoted microwave dielectric properties of the ceramics.