Dilatometric and optical properties of (CH3)(2)NH2Ga(SO4)(2) center dot 6H(2)O crystals in paraelectric and ferroelectric phases

摘要

Investigations of the temperature dependences of the dimension Li, optical path difference D-ij=L-i(n(j)-1), and refractive indices n(j) have been carried out for DMAGaS crystal, (CH3)(2)NH2Ga(SO4)(2) . 6H(2)O, in the range of 115-293 K for three principal directions of the optical indicatrix (i, j = p, m, g). The minima of the temperature dependences of anisotropy degree indices of the linear thermal expansion A(alpha) and refractive indices A(n-1) at temperature T-c reflect a small disordering of the crystal in the phase transition region. The coefficients of spontaneous linear electrostriction Q(L) have been found to be almost constant in the temperature range below T-c approximate to 136 K. The molecular refraction R, as a parameter of electron polarization due to high frequency light excitation, remains unchanged in the frame of 0.2% in the temperature range of 115-293 K. [References: 23]