Reevaluation of Raman spectra for KH2PO4 high-temperature phases

The common tetragonal form of KH2PO4 undergoes two high-temperature transfo rmations that have been studied extensively by vibrational spectroscopy. Bu t, because these changes are strikingly heterogeneous, the previously repor ted spectra, averages over polycrystalline and single crystal domains, have remained ill-defined. We recently identified the crystalline domains by po larization microscopy, physically isolated them, and determined their struc tures by X-ray diffraction (Subramony, J. A.; Lovell, S.; Kahr, B. Chem. Ma ter. 1998, 10, 2053-2057). Here, using micro-Raman spectroscopy, we have de convoluted the signals of the polycrystalline and crystalline domains, show ing that the inescapable pyro- and metaphosphate dehydration products are l ocalized in the polycrystalline material. Those debating whether the transf ormations are genuine structural phase transformations or are merely dehydr ation reactions can all be vindicated in certain parts of any one sample.