DETERMINATION OF THE PHOTOELASTIC COEFFICIENTS IN LITHIUM HEPTAGERMANATE CRYSTALS

The photoelastic (piezo-optic) property of the ferroelectric crystals lithium heptagermanate Li2Ge7O15 (LGO) were studied in para-and ferro- electric phases for different orientations. The value of stress optica l coefficient C-ijk (in Brewsters) along a, b, c-axes were determined at RT (291 K) and 278 K and were compared with some other ferroelectri c systems like Rochelle-salt (RS), potassium dihydrogen phosphate (KDP ) and ammonium dihydrogen phosphate (ADP). Large photoelastic coeffici ents and other properties like good mechanical strength, or transition temperature close to RT and stability in ambient environment favour L GO as a potential candidate for photoelastic applications.