Developments in Ceramic Materials Research

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216 R. Ramesh, H. Kara, Ron Stevens and C. R. Bowen create the pores. The spherical ATR results in rounded pores (Figure 1) whereas irregular PEO results in more irregular pore morphology (Figure 2). 2.3.1. Dielectric constant Figure 3 shows the variation in dielectric constant of 3-3 piezocomposites prepared using different techniques. Dielectric constant decreases with decreasing ceramic content. There is no significant difference in properties between PZT-Air and PZT-Polymer composites. This is due to the comparable permittivity values of air and polymer phases. It is also interesting to note that at ~ 60% PZT ceramic volume, where the 3-0 connectivity starts appearing, the permittivity deviates into two separate lines. This is due to the extensive cracks, revealed by cross-sectional SEM examinations, lying parallel to the surface. These cracks, which occur after green compaction due to relaxation of the elastic ATR spheres, prevent connectivity of the ceramic between the electroded surfaces, hence reducing the permittivity considerably. However, it should also be noted that pore anisotropy can also be a reason for this deviation between ATR and PEO samples since higher permittivity is obtained when specimen with pores align along the thickness direction compared to those normal to the thickness direction [32]. Figure 3. Variation of dielectric constant of 3-3 composites with ceramic volume fractions. 2.3.2. Piezoelectric Coefficients Piezoelectric coefficients depend strongly on the amount of piezoceramic component present in a piezocomposite, since this is the dominant contributor to the net piezoelectric property of the composite. The polymer component, being a passive material, contributes mainly to the mechanical properties and indirectly influences the piezoelectric properties of the composites as well.
Progress in Porous Piezoceramics 217 2.3.3. Hydrostatic Charge Coefficient Figure 4a shows the variation in piezoelectric charge coefficient with change in ceramic volume fraction. The hydrostatic charge coefficient (dH) increases with increasing piezoceramic volume fraction, reaching a broad maximum around 50-60 vol. % PZT, for PZT-Air composites. This is in good agreement with analytical models which indicate a broad maximum around 40-50 % PZT for dH [33]. It is difficult to draw similar conclusion from PZT-polymer composites due to the large scatter of the results. Decoupling of d33 and d31 coefficients by the polymer and ceramic struts along the direction transverse to the poling direction resulted a large reduction in d31 compared to d33, which in turn increases dH. For PZT-5H, the d33, charge per unit force produced in the direction of polarisation is almost the same in magnitude (513 pCN -1 ) as the combination of d31 and the d32, the charge on the transverse directions, but opposite in sign (-220 pCN -1 ). Therefore, if a hydrostatic force is applied to monolithic PZT-5H the charges cancel each other out. As seen in Figure 4b, an increase in the d33/d31 ratio with decreasing ceramic volume fraction indicates strong decoupling. Air provides better decoupling than the polymer. The d33/d31 ratio does not tail down as in dh which is due to the low values of the d33 and d31 charge coefficients at low ceramic fraction. Figure 4. Variation of piezoelectric hydrostatic coefficients of 3-3 composites with ceramic volume fractions; (a) charge coefficient (dH), (b) voltage coefficient (g H) and (c) Figure-of-Merit (d H g H). Polymer infiltration of the poled porous ceramics reduced the hydrostatic response of the composites considerably when compared to the PZT-air composites although there is still
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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22 Leslie G. Cecil Table 3. Mahalan
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24 Leslie G. Cecil Ixlú and Ch’i
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26 Leslie G. Cecil structures (D. R
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28 Leslie G. Cecil paste and Macanc
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30 Leslie G. Cecil Bieber, A. M. Jr
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32 Leslie G. Cecil Kepecs, S. M., a
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34 Leslie G. Cecil Schele, L., Grub
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36 Z. C. Li, Z. J. Pei and C. Tread
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62 I, % 100 80 60 40 20 0 T. T. Bas
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68 Fluorescence, a.u. 1 T. T. Basie
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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78 k, cm -1 20 18 16 14 12 10 8 6 4
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82 Photon counts 300 250 200 150 10
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84 Fluorescence, a.u. I transfer ,
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86 ln(I transfer (t)) -4.2 -4.4 -4.
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88 Fluorescence, a.u. I transfer ,
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In: Developments in Ceramic Materia
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Synthesis, Spectroscopic and Magnet
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a c Synthesis, Spectroscopic and Ma
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Transmission Transmission Transmiss
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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Intensity (a.u.) Intensity (a.u.) 8
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In: Developments in Ceramic Materia
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The Use of Ceramic Pots in Old Wors
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3.2. Wall-in Positions The Use of C
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IACC ( τ ) = t2 ∫ The Use of Cer
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where σ res is the scattering cros
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Page 260 and 261: 246 Li Chen The continuing evolutio
Page 262 and 263: 248 Li Chen the back contact cathod
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Page 266 and 267: 252 Li Chen Figure 6. Molybdenum mi
Page 268 and 269: 254 Li Chen Figure 8(a). I-V curve
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Page 274 and 275: 260 Li Chen [13] C.A. Spindt, K.R.
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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