Low Sintering Temperature of CuO-Fluxed Ag(Nb, Ta)O 3 Dielectric Ceramics
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Low Sintering Temperature of CuO-Fluxed Ag(Nb, Ta)O3 Dielectric Ceramics Chiping Wang 1, Thomas Shrout 1, Gaiying Yang 1, Hyo-Tae Kim2, Do-Kyun Kwon 1 and Michael T. Lanagan1 1 Center for Dielectric Studies, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 2 New Functional Materials Research Department, Korea Institute of Ceramic Eng. and Tech. Abstract Solid solutions in the Ag(NbxTa1-x)O3 (where 0 ≤ x ≤ 1) system exhibit excellent dielectric properties at microwave frequency including high dielectric constant (200100µm) is required to minimize interdiffusion in a polyphase assemblage and maintain a low TCC [5]. As shown in Figure 5, small particle sizes have a substantially higher TCC than for large particle size in CuO-free ANT composites [5]. The addition of CuO flux assists in maintaining a low TCC for small grain sizes. The effect of CuO addition and sintering temperature on the microstructure of ANT composites was explored. A scanning electron microstructure (SEM) results show the liquid phase at grain boundaries in Figure 6. Electron microprobe analysis (EMPA) at both the grain and grain boundary reveals that a Cu-rich phase is a continuous phase at the grain
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750 measured k series mixture rule log mixture rule
Dielectric constant
650
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-50
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Temperature (°C)
Figure 2. Comparison of measured k with different mixture rules. Measurements were made at 100KHz.
10 5
Strain (%)
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C uO free composite 1wt%CuO ad ded 2wt% Cu O added commercia l tape
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Temperature (°C)
Figure 3. TMA data of ANT composite powders and commercial LTCC tape.
100.6 100.4
Weight %
100.2 100 99.8 99.6 99.4 0
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Temperature (°C)
Figure 4. TGA of 45wt%ANT(35/65)+55wt%ANT(65/35) composite
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0.06 a b c d
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TCC
0 -0.02 -0.04 -0.06 -0.08 -0.1 -60
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Temperature (°C)
Figure 5. Temperature dependence of the dielectric properties for ANT composite. a. 45wt%ANT( 35/65)-55wt%ANT(65/35)+1wt%CuO, sintered at 900°C (~1µm). b. Small grain ANT composite from ref.5 (~1µm). c. Large grain composite from ref.5 (~50µm). d. 45wt%ANT( 35/65)-55wt%ANT(65/35)+2wt%CuO, sintered at 850°C (~1µm).
2 µm Figure 6. SEM analysis of a thermally etched ANT composite. The sintering temperature is 850°C and the annealing temperature is 750 °C 300
Cu peak (cps)
250
broad area on etched sample on grain boundary
200 150 100 50 0 5 104
5.1 104
5.2 104
5.3 104
5.4 104
Figure 7. Electron microprobe analysis. Cu peaks on grain boundary and grain
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boundary (Figure 7). Further, transmission electron microscopy (TEM) clearly shows that there is CuO at triple points in the microstructure (Figure 8). CuO is identified by EELS as shown in Figure 9. Table 1 summarizes the microwave dielectric properties of 1wt% and 2wt% CuO added ANT composites. It shows that sintering temperature and the amount of CuO addition in AN
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