ELECTRON-PARAMAGNETIC-RESONANCE INVESTIGATION OF THE FERROELECTRIC TRANSITION IN N2H5AL(SO4)(2)CENTER-DOT-12H(2)O CRYSTALS

The EPR spectra exhibited by the doped Cr3+ ions is sensitive to the r eported low-temperature ferroelectric transition in N2H5Al(SO4)(2) . 1 2H(2)O crystals. Structural informations that can be deduced from the experimental results include: (1) the appearance of merohedral twinnin g is concurrent with the onset of the structural phase transition; (2) the crystalline threefold symmetry, which is lost with the onset of t he structural phase transition, becomes the twin law relating the orie ntations of the component domains; (3) the crystal symmetry below the transition temperature is orthorhomhic; (4) the crystalline cubic axes of the high-temperature, cubic phase become the three crystalline two fold axes of the low-temperature, orthorhombic phase; and (5) a single Cr3+ species is detected in both the cubic and the orthorhombic phase s, which implies that all the Al3+ sites are crystallographically equi valent in both phases.