Uniaxial stress-induced phase transition, piezo-optical effect and optical domain studies in Cr-Cl boracite

Abstract

Abstract Uniaxial stress was applied to the single crystals of Cr3B7O13Cl [Cr-Cl] boracite along ⟨110⟩cub directions by means of a special rod constructed in our laboratory and adapted to low temperature polarized light microscopy. Evidence for a stress-induced first-order phase transition from the cubic 43m or the tetragonal 42m phase to the orthorhombic mm2 phase has been obtained by in situ observations of the ferroelastic/ferroelectric domains. The domain structure and the birefringence have been analyzed and correlated to the crystal symmetry of the initial and the induced phase. For a mechanical stress below the threshold strength, the piezo-optical effect has been disclosed, leading to a linear and reversible birefringence, e.g. δc = 4.8 × 10−4 under a stress of about 22 × 107 N/m2 (22.4 × 102 kg/cm2) at 285 K. The piezo-optical coefficient π44 in the 43m and 42m phases was found to be 1.5 × 10−12 m2/N (T = 264 K). In the spontaneous mm2 phase the application of a uniaxial stress gave rise to ferro...