Vibrational spectroscopy at high pressures. Part 30.—Raman study of silver, ammonium and potassium nitrates

Abstract

Raman spectra at high pressures are reported for AgNO₃, NH₄NO₃ and KNO₃. The new data strongly support a suggestion that AgNO₃ VI has the calcite structure, and are consistent with AgNO₃ III being of the CaCO₃ II type. The spectra of AgNO₃ IV cannot be assigned on the basis of either the CaCO₃ III or aragonite structures, but do imply that its structure is substantially different from that of AgNO₃ IV.

Phase transitions were found in NH₄NO₃ at 4.5 and 27 kbar. The close similarity of the lattice mode region of all three phases implies that the structures are all closely related to that of NH₄NO₃ IV.

Data for KNO₃ IV have been extended to 45 kbar and are shown to be consistent with the proposed structure based upon the space group Pmm2₁.