The dielectric properties of BaTi0.90Ga0.05Nb0.05O3 (BTGN and Ba0.60Sr0.40TiO3 (BST) ceramics prepared by the conventional solid-state route have been investigated. Their relative potential for microwave (MW) tunable applications was assessed by the figure of merit (K) defined as K = εro - εrv/εro · tan δo, (where εro and εrv are the relative permittivity at zero and 20 kV cm-1 at 10 kHz and tan δo is the loss at 10kHz or ∼1 GHz without DC bias). Fine-grained (∼2-3 μm) BTGN ceramics fired at 1500°C in air exhibit dielectric behavior characteristic of relaxor-type materials, with relative permittivity, εr, decreasing from ∼3082 to ∼2116 and dielectric loss, tan δ, increasing from 0.0035 to 0.0542 at 10 kHz and ∼1GHz, respectively. In contrast, large-grained (20-100 μm) BST ceramics exhibit a frequency independent εr of ∼5000 and show little variation of tan δ with frequency (0.0012 at 10 kHz and ∼0.0048 at 0.6 GHz). At 10 kHz, KBTGN = 91 and KBST = 367, whereas at MW frequencies KBTGN = 6 and KBST = 92. The large decrease in KBTGN at MW frequencies is attributed to a substantial increase of tan δ. The applicability of another relaxor-type BaTiO3-based ceramic, Ba(Ti0.70Zr0.30)O3, which was recently proposed as promising material for tunable MW applications, is also discussed. It is demonstrated that BaTiO3-based ferroelectric-relaxors may exhibit good tunable characteristics at 10 kHz; however, they are not competitive with BST for high K-factor MW applications.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Materials Chemistry