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FF3.4.1

Preparation of (Pb,Ca)(Fe0.5Nb0.5)1-yTiyO3 Perovskite Ceramics by a Reaction-Sintering Process Yi-Cheng Liou, Jen-Hsien Chen and Hsueh-Yung Lu Department of Electronic Engineering, Kun-Shan University of Technology, Tainan Hsien 710, Taiwan, R.O.C.

ABSTRACT Synthesis of (Pb0.45Ca0.55)(Fe0.5Nb0.5)1-yTiyO3 (y=0 and 0.1; PCFN and PCFNT) ceramics by a reaction-sintering process was investigated. The mixture of raw materials was pressed and sintered into ceramics without any calcination stage involved. The density 5.88g/cm3 (91.6% of the theoretical value) is reached at 1270oC for 2 h soak time in PCFN. Densification increased as B-site was substituted by 10% Ti and a density value 6.21g/cm3 (98.1% of theoretical value) was obtained after 2 h sintering at 1270oC. Grains are of 4.6-19.3µm in PCFN and 2.5-16.5µm in PCFNT at 1150-1270oC. Grain growth was retarded as the B-site was substituted by 10% Ti in PCFN ceramics.

INTRODUCTION Dielectric materials used in microwave devices have been widely investigated due to the fast growth of satellite and mobile communication systems. The microwave dielectric materials require a high dielectric constant (εr), a high quality factor (Q) and a small temperature coefficient of resonant frequency (τf) [1]. Pb-based complex perovskites were reported to have excellent dielectric properties as part of Pb ion in A-sites were substituted by Ca [2]. For (Pb0.45Ca0.55)(Fe0.5Nb0.5)O3 (PCFN) ceramic, εr=91 , Qxf=4950 GHz (at 3 GHz) and τf=+2.2 ppm/oC was obtained [2]. Kagata et al. reported that the (Pb1-xCax)[(Fe0.5Nb0.5)1-yTiy]O3 (PCFNT) system has excellent properties of εr over 95, Qxf >6000 GHz and τf 99%), Fe2O3 (>99%), Nb2O5 (99.8%) and TiO2 (99.9%). Appropriate amounts of raw materials for stoichiometric (Pb0.45Ca0.55) [(Fe1/2Nb1/2)1-yTiy]O3 (y=0 and 0.1, PCFN and PCFNT) were milled in acetone with zirconia balls for 12 h. After the slurry was dried and pulverized, the powder was pressed into pellets 12 mm in diameter and 1-2 mm thick. The pellets were then heated at a rate 10oC/min and sintered in covered alumina crucible at temperatures ranging from 1150oC to 1270oC for 2 h and 4 h in air. The density of sintered pellets was measured by water immersion method. The sintered pellets were analyzed by X-ray diffraction (XRD) to check phases formed in the pellets. Microstructures were analyzed by scanning electron microscopy (SEM).

RESULTS AND DISCUSSION A. PCFN X-ray diffraction results of PCFN specimens sintered for 2 h at 1150-1270oC are shown in figure 1. Perovskite phase is formed and the pyrochlore phase usually formed in Pb-based complex niobates is not observed. This proves the simple reaction-sintering process is effective in preparing perovskite PCFN ceramics. Figure 2 shows the density of PCFN ceramics as a function of a sintering temperature. The density increases with an increase of sintering temperature and reaches 5.88g/cm3 (91.6% of the theoretical value) at 1270oC for 2 h soak time. For 4 h sintering, density values are lower than that for 2 h sintering at 1150-