BIREFRINGENCE AND OPTICAL-ACTIVITY OF THE INCOMMENSURATE PHASE OF [N(CH3)4]2ZNCL4

By using a high-accuracy universal polarimeter, all the components of the optical-activity tensor g and birefringence DELTAn of [N(CH3)4]2ZnCl4 were measured in its paraelectric, incommensurate, and ferroelectric phases. Only one component, g23, was found to appear both in the incommensurate and ferroelectric phases, but all the other components vanished in the three phases. This fact mostly disagrees with the recent report of Dijkstra, Kremers, and Meekes, but partly agrees with our previous result. It was confirmed that the paraelectric phase was optically inactive although Dijkstra, Kremers, and Meekes reported that most components of the gyration tensor were nonzero. The results for DELTAn agree with those of Dijkstra, Kremers. and Meekes except for DELTAn(a). The source of these experimental disagreements are discussed.