HIGH-TEMPERATURE RIETVELD REFINEMENTS: SYSTEMATIC ERRORS OF MEASUREMENT. A. Kern and W. Eysel, Mineralogisches Institut der Universität, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany

High temperature powder diagrams are influenced by systematic errors of measurement, which may strongly affect high-temperature Rietveld refinements.

The most important ones of these errors were investigated using a BraggBrentano diffractometer (D 500, Siemens) with a heating equipment (HTK 2.3, Bühler) up to 1500deg.C:

* Beam Overflow

* Temperature gradient in the flat sample

* Texture from sample preparation

* (Multi-) Texture from nucleation effects during polymorphic transitions

* Reflections from the material of the sample carrier.

These errors and how to take them into account and minimize them, were studied for selected materials: [[alpha]]-A1₂O₃, Quartz, MgO, Li₂SO₄, Ag₂SO₄.

Among others the refinement of a two phase sample (Li₂SO₄+Pt) will be presented, in which both phases exhibit multitexture. The refinement was carried out by using simultaneously the Rietveld method for Li₂SO₄ and the Whole Powder Pattern Fit method for Pt.