HRTEM observations of sol-gel derived YAG and alumina/YAG thin films

This paper reports on the preparations of Thin films of YAG and YAG/alumina mixtures by gelling a sol across a TEM grid. The grids were heat-treated to temperatures as high as 1550 degrees C. The resulting ceramic thin films were observed by standard and high resolution TEM techniques. Ion- milling, carbon coating, or other specimen preparation was not necessary. The phase and microstructure evolution, as well as pore structure evolution and spheroidization of film edges could be easily observed. Abnormal grain growth was observed in yttrium-aluminum garnet (YAG) films. Lattice images were taken of the matrix, abnormal grains, and structures that evolved from the abnormal grains at higher temperatures. The grain size preceding abnormal grain growth was 20--50 nm. The abnormal grains were composed of 20--50 nm subgrains with up to several degrees of misorientation. High resolution observations were also made of small (<0.2 μm) YAG inclusions in alumina. An orientation relationship of (111)[0 111]alumina parallel(112)[0 1]YAG was observed. This orientation relationship was not observed in large inclusions