HIGH-PRECISION MEASUREMENT OF TEMPERATURE FACTORS FOR NIAL BY CONVERGENT-BEAM ELECTRON-DIFFRACTION

Convergent-beam electron diffraction is applied to measure the tempera ture factors of the intermetallic phase NiAl with high accuracy. The p atterns are recorded in an energy-filtering transmission electron micr oscope at zero energy loss using a slow-scan CCD camera. The specimens were tilted in systematic row orientation. In this new approach, data are extracted from the bright-field disc as well as from several high -order dark-field discs along line scans. The temperature factors are determined by fitting Bloch-wave simulations to the intensity profiles . The harmonic approximation for temperature factors is used. For B2-p hase NiAl, mean thermal displacements u(Ni) = 5.5 +/- 0.1 and u(Al) = 5.7 +/- 0.1 pm are obtained at 100 K. A very detailed error analysis i s given, and stochastic and systematic errors are discussed and quanti fied.