Complex crystallographic study of potassium sulfate-ammonium sulfate solidsolutions

The variation in the morphological, optical, and crystallochemical characte ristics of a continuous series of(NH4,K)(2)SO4 solid solutions have been co nsidered. It has been established that both habit and optical sign of the c rystals of these solid solutions change twice. In the composition range stu died, the unit-cell parameters have two anomalous ranges of their variation : the dependences of a and c on the (NH4)(2)SO4 content show the inflection s at 8-13 mol % (NH4)(2)SO4, whereas the dependences of a and b on the (NH4 )(2)SO4 content show the discontinuities at 43-60 mol % (NH4)(2)SO4 Th comp arison of the experimental and theoretical intensity ratios, I-002/I-013, s hows that crystals with different degrees of order with respect to K+ and t he (NH4)(+) cations can exist. The results obtained indicate that the (K,NH 4)(2)SO4 solid solutions are far from being ideal, which is seen from the n onlinear variation of the properties studied for crystals of different comp ositions. The phase diagram of the system has been refined.