Scattering defect

The thermal conductivity of is much higher than that of the fee transition metal carbides. The lower thermal conductivity of fee carbides has been attributed to their generally nonstoichiometric composition and hence the higher concentration of phonon scattering defects in the lattices, but can probably be explained by the stronger covalent bonding in WC and hence the higher efficiency of the heat transport by phonons. 

The low thermal conductivity of bulk YSZ results from the low intrinsic thermal conductivity of zirconia and phonon scattering defects introduced by the addition of yttria. These defects are introduced because yttria additions require the creation of vacancies to maintain the electrical neutrality of the ionic lattice. Since both the yttrium solutes and the vacancies are effective phonon scattering sites the thermal conductivity is decreased as the yttria content is increased. 

Kato, M. Yoshida, T. Ikeda, Y. Kitagawara, Y. (1996). Transmission electron microscope observation of "IR scattering defects" in as-grown Czochralski Si crystals. Japanese Journal Applied Physics, Vol. 35, No. 11, pp. 5597-5601, ISSN 0021-4922. 

In order to check the potential substitution of Tb3Ga60i2 by Tb3 [Sc2 Lua ](Al3)Oi2 the optical quality of the crystals was further analyzed. The photograph of a 10 mm long sample with 3 nun in diameter under crossed polarizers is shown in Fig.l6 (left). It is seen that the crystal is very homogeneous, free from scattering, defects,... 

Four volumetric defects are also included a spherical cavity, a sphere of a different material, a spheroidal cavity and a cylinderical cavity (a side-drilled hole). Except for the spheroid, the scattering problems are solved exactly by separation-of-variables. The spheroid (a cigar- or oblate-shaped defect) is solved by the null field approach and this limits the radio between the two axes to be smaller than five. 

Experiments have shown promising results. For components in sintered state a number of components with different defects have been able to reject based on reference measurements on components without defects. For components in green state the results vary, cracks have been able to detect, but density differences not. For both measurements on components in green and sintered state scatter between measurements was observed to be substantial. 

The beam-defect interaction is modelled using Kirchhoff s diffraction theory applied to elastodynamics. This theory (see [10] for the scattering by cracks and [11] for the scattering by volumetric flaws) gives the amplitude of the scattered wave in the fonn of coefficients after interaction with defects and takes account of the possible mode-conversion that may occur. 

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