In this paper, recent progress made in the field of high-temperature x-ray diffraction (HT-XRD) is presented. A substantial part of this progress is due to the introduction of a multilayer x-ray mirror in the x-ray optical system. The parabolic shape of the mirror layers transforms the initially divergent x-ray beam into a parallel x-ray beam without a significant loss of intensity. The diffraction angles of the parallel beam are insensitive to changes of the sample surface position, which occur e.g. due to thermal expansion of the sample or its support during in-situ high temperature tests. Also, the parallel beam, when incident on the surface sample under a low angle, covers a large area on the sample. To profit from this benefit during high temperature tests, particular attention was paid at obtaining a large, uniform heated zone. With the new HT-XRD system, a series of ceramic materials was investigated. In particular, the thermal expansion anisotropy of the hexagonal beta -Si3N4-phase is quantified. Also, the crystallisation of an initially amorphous intergranular phase in a hot-pressed Si3N4 is observed in-situ, at 1300 degreesC. In addition, it will be shown how the system was used to detect the crystallisation of ultra-thin (down to 2.5 mn) amorphous ZrO2 and HfO2 films, which were deposited on Si-substrates. For the first time - to the author's knowledge - diffraction spectra were obtained at temperature from films of this low thickness.
