Optical and dilatometric properties of (CH3)2NH2Al(SO4)2 •6H2O crystals in paraelectric and ferroelectric phases

Experimental investigation of the thermal linear expansion l(T) and temperature dependencies of the interference optical path difference D(T) were carried out for (CH3)(2)NH2Al(SO4)(2). 6H(2)O crystal, in the range of 120-310 K for three crystal physical directions. Decrease in electrostriction coefficients g of crystal was observed on approaching the phase transition point T-c approximate to 150 K in ferroelectric phase. Relative temperature changes of the lengthening delta l/l and refractive index delta n/(n - 1) are of the same order of magnitude. Peculiarities of temperature dependence of dilatometric and optical parameters of (CH3)(2)NH2Al/(SO4)(2). 6H(2)O testify for qualitative reconstruction of chemical bonds in the crystal when temperature changes in the same phase.