Thermal expansion and optical properties of DMAGS crystals around their phase transitions

This paper presents the results of the investigations of thermal expansion, birefringent and electrooptic properties of NH2(CH3)(2)Ga(SO4)(2) . 6H(2)O (DMAGS) crystals. It has been shown that the ferroelectric phase in DMAGS is limited by the first-order phase transitions at T-c1(h) = 136 K and T-c2 (h) = 119 K. Both phase transitions are connected with a considerable recon struction of the crystalline structure. Absence of the linear electrooptic effect below T-c2 reflects the disappearence of spontaneous polarization al ong the investigated X-direction.