Microwave dielectric properties and thermally stimulated depolarization of Al‐doped Ba ₄ (Sm,Nd) _9.33 Ti ₁₈ O ₅₄ ceramics

Abstract

Abstract Ba 4 (Sm 0.15 Nd 0.85 ) 9.33 Ti 18‐ z Al 3 z /4 O 54 (BSNT‐ z Al, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid‐state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten‐bronze‐like solid solutions. With a small amount of Al substitution, the relative dielectric constant (ε r ), and the temperature coefficient of resonant frequency ( τ f ) values decreased, whereas the quality factor ( Q × f ) substantially increased by approximately 50%. The defect‐related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across‐grain‐boundary oxygen vacancies ( ) vanished, whereas that of defect dipoles ( ) appeared at relatively low temperatures. Therefore, in the BSNT‐ z Al ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of ε r = 67.33, Q × f = 16 530 GHz, and τ f = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.