ON THE NONSTATISTICAL SUBSTITUTION OF POTASSIUM WITH AMMONIUM IN THE K2SO4-(NH4)2SO4 SYSTEM

The FT-IR spectra of protiated and partly (5 %) deuterated solid solutions of potassium and ammonium sulfate ([K1-x(NH4)x]2SO4) were recorded at temperatures between 295 and 76 K. The number of different N-D stretching bands was used as a criterion for the presence of one or two types of crystallographically different ammonium ions in the mixed crystal. For 0 < x < 0.2, ammonium ions of only one type are present. However, for 0.2 < x < 0.5, the number of the N-D stretching bands and their shape strongly indicate the presence of two types of NH4 ions. The possible reasons for this peculiar behaviour are discussed.