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 reported low-temperature ferroelectric transition in N2H5Al(SO4)(2) . 12H(2)O crystals. Structural informations that can be deduced from the experimental results include: (1) the appearance of merohedral twinning is concurrent with the onset of the structural phase transition; (2) the crystalline threefold symmetry, which is lost with the onset of the structural phase transition, becomes the twin law relating the orientations 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 twofold axes of the low-temperature, orthorhombic phase; and (5) a single Cr3+ species is detected in both the cubic and the orthorhombic phases, which implies that all the Al3+ sites are crystallographically equivalent in both phases.