DIELECTRIC-DISPERSION IN FERROELECTRIC (CH3)2NH2GA(SO4)2.7H2O CRYSTAL

This paper presents the results of the investigation of the spontaneous polarization, dielectric anisotropy and dispersion in the new ferroelectric, dimethylammonium gallium sulphate. On cooling, the crystal undergoes two first-order phase transitions at T(c1) = 136 K and T(c2) = 106 K with the spontaneous polarization along the x-axis between T(c1) and T(c2). In the vicinity of T(c1) the crystal shows a critical slowing down of polarization fluctuations. In the far paraelectric phase, ferroelectric dispersion of the Debye-type is caused by a single relaxational soft mode related to the flipping motion of the dimethylammonium groups in a double well potential with an activation energy 0.09 eV = 7.6 k T(c1) in the paraelectric phase. Near T(c1) and in the ferroelectric phase the ferroelectric dispersion overlaps with the domain wall dispersion and causes a complicated dielectric spectrum.