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.

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