• PDF / 115,051 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 41 Downloads / 248 Views

DOWNLOAD

REPORT

---

0966-T10-12

Dielectric Properties of Cr2O3 Doped (Ba,Sr,Ca)TiO3 Ceramics for Tunable Microwave Devices Bing Qin, Dengren Jin, Jinrong Chen, and Zhongyan Meng School of Materials Science and Engineering, Shanghai University, No.149 Yanchang Rd., Shanghai, 200072, China, People's Republic of ABSTRACT Cr2O3-doped (Ba0.55Sr0.4Ca0.05)TiO3 ceramics were fabricated by the mixed-oxide method. Their dielectric properties were investigated with the variation of Cr3+ doping concentrations (0~2.0mol%). All the BSCT specimens owned dense and homogeneous structure. Doping of Cr3+ could reduce the Curie temperature and their dielectric constant peak values, and improve the thermal stabilities of their dielectric properties. Both the dielectric constant and dielectric loss of the BSCT ceramics were reduced by doping Cr ions when the dopant concentration was lower than 1.5mol%. 1.0mol% Cr-doped BSCT specimens are expected to be the candidate materials for microwave tunable devices, whose tunability, dielectric constant and loss were 16.1%, 2700 and 0.24% respectively. INTRODUCTION The BST (BaTiO3-SrTiO3 solid solution) system is well known for its strong response to the applied DC electric field. This property is very attractive and has been used to develop microwave devices such as phase shifters, frequency agile filters, and tunable capacitors [1]. The optimal electronic parameters of the dielectric materials for phase array applications should have a moderate to low dielectric constant, low dielectric loss, and high dielectric tunability [2]. Various methods have been investigated to lower the dielectric loss and dielectric constant of BaTiO3-based ceramics for tunable microwave device applications [3, 4]. It is widely known that the dielectric properties of BST can be modified through partial substitution of isovalent or heterovalent cations at Ti sites (B-site doping) and Ba sites (A-site doping): generally the acceptor (Mn, Fe, Al)-doped BST can decrease the loss tangent [5,6] while Nb-doped BSCT can increase the tunability but the dielectric loss increased as well [7]. All above show that dielectric properties of ceramics were strongly affected by doping ions. (Ba,Sr)(Zr,Ti)O3 ceramics were investigated and results showed that the dielectric properties were promising but it had ferroelectric-relaxor behaviors. [8] A great deal of data showed that the ferroelectric-relaxor behaviors would restrict the range of application frequency, because the dielectric loss of relaxor samples would become very large at the microwave frequency [9, 10]. Recently, (Ba,Sr,Ca)-TiO3 has been shown as an alternative candidate material to tunable materials in the fabrication of ceramic capacitors [11,12]. Ca is located at the same subgroup of Ba and Sr, and CaTiO3 is always in paraelectric phase. In addition, the solid solution of BaTiO3-SrTiO3-CaTiO3 exists in a single phase for a wide range of compositions [13]. So we

may find the ceramics with good dielectric properties by modifying the rates of Ba, Sr and Ca. In our previous work we investig