Transmission and reflection electron microscopy of ceramic materials

Transmission and reflection electron microscopy (TEM and REM) have been used for studying ferroelectric and some other ceramic materials. High-resolution transmission electron microscopy (HREM) has been used to study ferroelectric domain boundaries in barium titanate and lead zirconate titanate ceramics. The strain fields in the vicinity of 90{dollar}spcirc{dollar} domain boundaries have been revealed by Fourier analysis of HREM images. 180{dollar}spcirc{dollar} a-a domain boundaries in barium titanate have also been studied in dark field imaging as well as bright-field imaging. It is also found that domain sizes decreases as the thickness of film decreases and that the domains in thin films of BaTiO{dollar}sb3{dollar} disappear at lower temperatures than the bulk transition temperature of 122{dollar}spcirc{dollar}C, and that domain sizes decrease as the film thickness decreases. These phenomena may indicate a "weak ferroelectricity" of a thin ferroelectric film, which is a transition state from ferroelectric to paraelectric. It is suggested that these phenomena are due to the relaxation of constraints in thin films. Preliminary in-situ observations of behaviors of ferroelectric domain boundaries under applied electric fields have been attempted. New "c" domains have been found being formed on the original 90{dollar}spcirc{dollar} a-a domain boundaries when the electric field is applied and maintaining their shapes and sizes after the field is removed. REM has been used to study the intersections of ferroelectric domain boundaries with surfaces of crystals. It is found that the contrasts are due to the differences of diffraction conditions. In particular, it is suggested that the contrast of 180{dollar}spcirc{dollar} c-c domain boundaries in REM may be related to the distribution of adsorbed charges on the surfaces of domains. REM has also been used to study other planar defects such as stacking faults. Stacking faults emerging on the surface of gallium arsenide crystals may be identified by the bounding dislocations, the phase contrast of the surface steps associated with the stacking fault, and a weak contrast from the dynamical scattering in the faulted part. HREM has also been used to study the grain boundaries in the ceramic electrolytes for solid oxide fuel cells (SOFC). It is found that pores may exist on the grain boundaries of calcia-stabilized-zirconia, which may act as blocks for ion transport across grain boundaries. Few defects have been found on the grain boundaries in other fluoride structure oxide and perovskite oxide electrolytes.