SOME NEW ASPECTS ABOUT THE ELIMINATION OF SYSTEMATIC-ERRORS IN HAUP MEASUREMENTS

In recent years the HAUP method, which allows determination of simulta neously occurring birefringence and optical activity of crystals, has extensively been applied in order to answer the question of whether th ere is an optical activity in the incommensurate phase of A(2)BX(4)-ty pe crystals or not. Especially in the case of tetramethylammonium tetr achlorozincate (TMAZC), which was investigated most thoroughly, severa l authors reported contradictory results. In order to establish possib le causes of these discrepancies we performed HAUP measurements on sev eral test samples of quartz and MgF2. The results revealed an essentia l influence of sample preparation and gave us a better insight into th e systematical errors, primarily the so-called delta chi error, the pa rasitic ellipticities of polarizer and analyser, and a further paramet er k(offset) representing the ellipticity induced by the sample's surf aces. This made it possible to understand some of the reasons for the diverging results published for A(2)BX(4)-type crystals so far.