The Preparation of Bi-Layered SrBi2Ta2-xVxO9 Ceramics (0.1≦x≦0.4)

V2O5 is used to substitute Ta2O5 site of the SrBi2Ta2O9 ceramics to form SrBi2Ta2-xVxO9 composition, where 0.1 x 0.4 ≦ ≦ . The sintering and the dielectric properties of SrBi2Ta2-xVxO9 ceramics have been developed. For all SrBi2Ta2-xVxO9 composition, the crystal intensities of the (0,0,l) planes increase with the increase of sintering temperature and saturate at 1050C-sintered ceramics, and the increase in the crystal intensities of the (0,0,8) and (0,0,10) planes are more obvious. For the same sintering temperature, the crystal intensities of the (0,0,l) planes increase with the increase of V2O5 content and saturate at SrBi2Ta1.7V0.3O9 ceramics. This study will show that the sintering temperature and V2O5 content have large influences on the maximum dielectric constants (εTc) and the Curie temperatures of SrBi2Ta2-xVxO9 ceramics. Introduction The layer structured bismuth compound ferroelectric has the general formula: An-1Bi2BnO3n+3, where A is usually a divalent ion, such as Sr, Ba, or Pb, and B is Ti, Nb, or Ta [1-3]. Within the bismuth family, SrBi2Ta2O9 ceramics had attracted the most attention in the past years [4-7]. Although the polarization of SrBi2Ta2O9 ceramics is less than the competing Pb(Ti,Zr)O3-based materials, the bismuth-layer compounds are much stable to polarization fatigue free property, i.e. almost no charge loss will happen when polarization is reversed many cycles. In the SrBi2Nb2O9 composition, the substitution of Nb2O5 by V2O5 will lower the sintering temperature and produce materials with enhanced dielectric properties that are useful in many applications [8]. In this study, we are interesting to investigate ceramic materials based on SrBi2Ta2O9 composition, V2O5 is used to substitute for Ta2O5 to form the SrBi2Ta2-xVxO9 compositions. Bulk SrBi2Ta2-xVxO9 materials are sintered at different temperature and their morphologies and crystal phases are examined. The temperature-dependent dielectric characteristics are also investigated as a function of sintering temperature and V2O5 content. Experimental Procedures Reagent-grade raw materials of SrCO3, Bi2O3, Ta2O5, and V2O5 with higher than 99.5% purity were used as starting materials, mixed according to the composition SrBi2Ta2-xVxO9 (x=0.1, 0.2, 0.3, and 0.4, respectively) and ball-milled for 5h with deionized water. After dried and ground, the powder was calcined at 850C for 3h. After calcination and ground again, then polyvinylalcohol (PVA) was added as a binder. The calcining powder was uniaxially pressed into pellets in a steel die. After debindering, sintering of these pellets was prceeded from 900C to 1100C for 4h. The crystal structures of the SrBi2Ta2-xVxO9 ceramics were investigated using XRD patterns, and the morphologies were observed by using scanning electronic micrograph (SEM). The sintered ceramics were painted with Ag-Pd paste and sintered at 700C for 15min. Temperature-dependent dielectric characteristics were measured at 1MHz with an oscillating amplitude (50mV) by an HP4194 impedance analyzer, putting the sintered ceramics in a temperature-programmable testing chamber. Results and Discussion The changes in density and grain size can be seen in the SEM photographs of selected SrBi2Ta2-xVxO9 ceramics and the results are shown in Fig.1. For 950°C-sintered SrBi2Ta1.9V0.1O9 ceramics, as Fig.1(a) shows, the pores are still observed and the grain growth iis not obvious. Further increasing the sintering temperature to 1000°C, homogeneously fine microstructures with less pores are observed, as shown in Fig.1(b).The temperature for SrBi2Ta2O9 ceramics to reveal homogeneous grain growth is 1200C (not shown here), this result suggests that the sinterability of SrBi2Ta2-xVxO9 ceramics has improved due to the V2O5 substitution. The pores of all SrBi2Ta2-xVxO9 ceramics decrease and the grain sizes increase with the increase of sintering temperature independent of V2O5 content. Sintered at 1050C, as Figs.1(c), 1(d), and 1(e) are compared, the grain sizes apparently increase as x changes from 0.1 to 0.2 and the grain sizes slightly increase as x change from 0.2 to 0.4. (a) (b) (c)