Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents Study of (1−x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xTiO₂ Ceramics

Abstract

Microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of (1−x)Ba0.6Sr0.4La4Ti4O15–xTiO2 (x = 0, 0.01, 0.02, 0.05, and 0.1) ceramics were studied. X‐ray diffraction analysis indicates that the specimens show a hexagonal perovskite structure; however, with an increase of x to 0.1, TiO2−δ as a secondary phase can be detected in the ceramics. The variation of TiO2 content has a significant effect on the dielectric properties of (1−x)Ba0.6Sr0.4La4Ti4O15–xTiO2 at microwave frequency. The dielectric permittivity of ceramics increases from 44 to 49 with the increase of TiO2 content. The Qf value is in the range of 39 300–53 400 GHz. However, the temperature coefficient of resonant frequency (τf) changes from −7.5 to–9.4 ppm/°C, and then turns to +3.9 ppm/°C. A near zero τf value can be obtained by tuning the content of TiO2 addition. TSDC was also employed to analysis the extrinsic loss mechanism. Utilizing a fixed polarization condition, the TSDC relaxation peaks are present, which are generated by oxygen vacancies. And the concentration of oxygen vacancies increases with the increase of TiO2 content. It can be concluded that the extrinsic dielectric loss is dominated by microstructure and oxygen vacancy defects.

Microwave dielectric properties and thermally stimulated depolarization of Al‐doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

“…The microwave dielectric properties of Ba 4 (Sm 0.15 Nd 0.85 ) 9.33 Ti 18‐ z Al 3 z /4 O 54 (BSNT‐ z Al) ceramics and their correlation with the z value were determined. In addition, the thermally stimulated depolarization current (TSDC) technique can provide semiquantitative information of dielectrics on the types (such as trap charges, defect dipoles, and space charges), concentrations, and activation energies of the defects . At present, TSDC has been widely used to clarify the polarization mechanism of various types of dielectric ceramics and to explore the relationships between defects and dielectric performance.…”

Understanding microwave dielectric properties of (1−x)CaTiO3–xLaAlO3 ceramics in terms of A/B-site ionic-parameters

“…The phase structure of the CTLA ceramics with x ≤ 0.5 exhibited an orthorhombic perovskite structure similar to that of CaTiO 3 , while the phase structure of the CTLA ceramics with x＞0.5 exhibited a rhombohedral perovskite structure similar to that of LaAlO 3 . This indicates a phase transition at a composition close to x = 0.5.…”

“…In the CTLA ceramics, Ti 4+ and Al 3+ are distributed uniformly throughout the B-sites. The broad mode around 800 cm −1 (A 1g ) which indicates the short-range order of B-site cation was absent in the spectra from both pure LaAlO 3 and CaTiO 3 but present in the spectra of CTLA (0.3 ≤ x ≤ 0.7) ceramics. This mode is typically observed in complex perovskite solid solutions [24].…”

“…Modern wireless communication devices, such as filters, oscillators, and dielectric resonators, require microwave dielectric ceramics with appropriate dielectric constant ( r  ≈45), high quality factor value (Q × f ＞ 30 000 GHz), and near-zero temperature coefficient of resonant frequency ( f  ≈ 0) [1][2][3]. To meet the requirements of current and future systems, the perovskite family of materials have been extensively studied among a number of dielectric material systems.…”

“…However, large-scale production of these materials has been limited because preparation of most CaTiO 3 -REAlO 3 ceramics requires high sintering temperature (＞1450 ℃) and because of the high cost of rare earth elements [5]. Among CaTiO 3 -REAlO 3 materials, CaTiO 3 -LaAlO 3 stands out as a candidate with suitable microwave dielectric properties that could meet the need of microwave dielectric filters used in mobile communication base stations because of the good thermal stability of the ceramics [6,7] and the relatively low cost of the starting materials.…”