Defect relaxation and microwave dielectric response of Ca1-xSrxLa4Ti4O15 hexagonal perovskite ceramics with 5-layer shifted structure

The medium-permittivity Ca 1- x Sr x La 4 Ti 4 O 15 (CSLT, x  = 0.2, 0.4, 0.6, 0.8) ceramics are synthesized by high temperature solid-phase reaction method, and the impacts of Sr 2+ substitution on the microwave dielectric properties and defect behaviors are investigated in depth. X-ray diffraction (XRD) and Raman spectra demonstrate that Sr 2+ successfully incorporates the lattice to form a solid solution . Structure refinement and transmission electron microscope (TEM) indicate the formation of a 5-layer shifted hexagonal perovskite ceramic consisting of AO 3 layers stacked in a “ccchh” fashion. The dielectric constant of the well-sintered CSLT ceramics increases slightly with the increase of Sr 2+ substitution, while the Q × f value fluctuates within a small range of 41,100 GHz–48,750 GHz. Correspondingly, the prominent microwave dielectric properties of the Ca 0.6 Sr 0.4 La 4 Ti 4 O 15 ceramics are ε r  = 47.0, Q × f  = 48,750 GHz, and τ f  = −10.5 ppm/°C. The thermal relaxation behaviors of the defect are systematically explored employing thermally stimulated depolarization current (TSDC) measurements, from which oxygen vacancies and defect dipoles are considered as the main defect types in ceramics. In addition, the ultra-fast discharge time ( t 0.9  = 15 ns) indicates that the CSLT ceramics have distinguished pulse discharge performance, promising for the applications of microwave capacitors.