Inversion domain boundaries (IDB's) in ZnO ceramics, associated with Sb2O3 doping, have been characterized using a range of electron microscopy techniques. The IDB's lie primarily on basal planes, but frequently are stepped along prismatic planes. The basal IDB can be characterized as (i) an inversion that causes an antisite exchange of cations and anions across the boundary, (ii) an effective displacement of the sixfold screw axis in the wurtzite structure vectors by a translation of 1/3 and (iii) a displacement normal to the boundary. Significant Sb segregation is detected in the basal IDB segments in agreement with previous work, and in ceramics doped with Sb2O3 and Bi2O3. These IDB's contained both Sb and Bi, suggesting that while Bi does not participate in IDB nucleation, it resides in the boundary. Comparison of experimental and calculated HREM images suggests that the IDB is composed of a monolayer of Type I (111) zinc antimonate spinel, consisting of a single layer of octahedrally coordinated zinc and antimony cations.
The polymorphism of enstatite (MgSi03) is reviewed. Three stable phases occur -clinoenstatite, orthoenstatite, and protoenstatite, being stable at low, intermediate, and elevated temperatures, respectively -and new data concerning their crystallization from synthetic glasses are summarized. The phase transformations between these polymorphs are discussed, particularly their sensitivity to shear stresses. Finally, the possibility of using one or more of these transformations for toughening silicates is considered.
BaTi409 powder prepared by calcining BaCOj and Ti02 powders was sintered to over 97% of theoretical density. Less than 5% Ba2Ti9OZO occurred as a second phase in "pure" BaTi409, and A1203 impurities from processing formed isolated hollandite (-BaA12Ti6*3316) grains, which were identified by fringes in bright-field TEM images. For pure BaTi409 at 1 MHz, a dielectric loss (tan 6) of 5 X and dielectric constant of 39 were recorded. Hollandite impurities were found to increase tan S by 2 orders of magnitude, whereas firing in oxygen decreased tan 6 by an order of magnitude.[
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