HREM studies of structure, defects and phase transformation in zirconia and Mn stabilised zirconia

Abstract

Zirconia is known to exist in three different structure types: monoclinic, tetragonal and cubic. Monoclinic is the room temperature form that transforms to tetragonal and finally to cubic at progressively higher temperatures. The monoclinic to tetragonal transformation is reversible, exhibits hysteresis and has been widely studied by thermal analysis, high temperature x-ray diffraction and electron diffraction. This transformation has an undesirable effect on some materials properties. The cubic form of zirconia has been stabilised with yttria, calcia, alumina and magnesia. The decomposition of zirconium carbonate and zirconium manganese carbonate to the respective oxides and their phase tranformation has been studied in situ by electron diffraction and high resolution electron microscopy (HREM) and the results are reported here.The carbonates used in these studies were precipitated from their aqueous solution. Thin crystal fragment were dispersed on holey carbon grids using a suspension in ethanol. A JE0L 4000EX microscope, with double tilt goniometer and on-line Digital MicroVAX II image-analysis system, operating at 400KV, was used for HREM studies.