Electric Field‐Dependent Dielectric Properties and High Tunability of Porous Ba_0.5Sr_0.5TiO₃ Ceramics

Abstract

Porous Ba0.5Sr0.5TiO3 (BST) ceramics were fabricated by the traditional solid‐state reaction process, and their structural, microstructural, dielectric, and tunability properties were systemically investigated. Compared with the fully dense BST samples, porous samples exhibit smaller grain sizes, a more uniform microstructure, and much lower dielectric constants, while at the same time, exhibiting little increase in tunability, which is beneficial to the development of microwave‐tunable applications. At a frequency of 10 kHz and a temperature of 18°C, as porosity increased from 0% to 28.8%, the dielectric constant of the BST ceramics (under zero bias field) decreased from ɛr(0)∼1690 to ɛr(0)∼990, while the dielectric losses were still less than 0.2%, and the tunability increased from 17.6% to 19.6% (2.6 kV/mm).

The model of electric field dependent dielectric properties for porous ceramics

“…A number of groups of nonferroelectric additives such as MgO, MgTiO 3 , Al 2 O 3 , and so on have been introduced to BST-based ceramics in order to dilute the dielectric constant and suppress the dielectric loss, but unfortunately the dielectric tunability is reduced as well. [6][7][8][9] Up to now, there is little report fully satisfying all the requirements, and the general trend that indicates that the higher the dielectric constant, the higher the tunability generally holds in ferroelectric tunable materials. 10 However, in our previous work, the BST-based porous ceramics showed an interesting "discrepancy," which possessed low dielectric constant but still maintained the relatively high tunability.…”

The Effect of Isostatic Pressing on the Dielectric Properties of Screen Printed Ba0.5Sr0.5TiO3 Thick Films

“…If we consider the thick films as composites of air and BST bulk materials, more pores would dilute the tunability of BST ceramics [20]. It is noted that the tunability for the thick film is more than 3 times larger than their peer bulk ceramics [17,20]. Table 2 compares in detail the tunability and the dielectric properties of the current work with reported publications.…”

“…At room temperature, the dielectric loss at 10 kHz in the film after pressing is 0.0028, compared with 0.0037 without pressing. Compared with a bulk BST material sintered at 1350 ∘ C, with the dielectric constant above 1500 and dielectric loss in the range of 0.002 [20], the isostatic-pressure-treated screen printed BST thick films show prominent modification on dielectric constant while maintaining the low dielectric loss, which is suitable for microwave device designs.…”

“…A porous ceramic can be considered dual-phase system composed of bulk ceramic and air pores. Considering that the dielectric constant of air is around 1, less air pores will lead to higher dielectric constant [20]. The dielectric losses in the sample with isostatic pressing treatment are generally lower than unpressed one.…”

“…When the electric field is set to 200 kV cm −1 , the tunability ( = ( (0) − ( ))/ (0)) with the isostatic pressing treatment reaches 61.7%, compared to 48.3% of the film without isostatic pressing. If we consider the thick films as composites of air and BST bulk materials, more pores would dilute the tunability of BST ceramics [20]. It is noted that the tunability for the thick film is more than 3 times larger than their peer bulk ceramics [17,20].…”