Large Basal Spacing Research Articles

An x-ray and electron microscope study of the compound PbAl 12O 19

The new compound PbAl 12O 19 has been prepared both by solid state reaction between lead oxide and freshly precipitated aluminum hydroxide and by reaction between lead oxide and ammonium alum. It has also been prepared in single-crystal form from a lead oxide-fluoride flux. It is hexagonal with a o = 5.554 A ̊ and c o = 21.94 A ̊ . It has a magnetoplumbite-like structure forming in plates from which the basal spacing can be directly measured in an x-ray diffractometer. The space group is P6 3/mmc. The large basal spacings have been observed directly by transmission electron microscopy. The composition was determined by x-ray spectroscopy. Using transmission electron microscopy, numerous dislocations were found on basal-plane sections of the flux-grown sample. These dislocations, having Burger's vectors in the 〈112̄0〉 directions, show evidence of dissociation into partials.