Optical and dilatometric properties of (CH3)(2)NH2Al(SO4)(2) center dot 6H(2)O crystals in paraelectric and ferroelectric phases

Experimental investigation of the thermal linear expansion l(T) and tempera ture dependencies of the interference optical path difference D(T) were car ried 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 coef ficients g of crystal was observed on approaching the phase transition poin t T-c approximate to 150 K in ferroelectric phase. Relative temperature cha nges 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 testi fy for qualitative reconstruction of chemical bonds in the crystal when tem perature changes in the same phase.