Reevaluation of Raman Spectra for KH₂PO₄ High-Temperature Phases

Abstract

The common tetragonal form of KH2PO4 undergoes two high-temperature transformations that have been studied extensively by vibrational spectroscopy. But, because these changes are strikingly heterogeneous, the previously reported spectra, averages over polycrystalline and single crystal domains, have remained ill-defined. We recently identified the crystalline domains by polarization microscopy, physically isolated them, and determined their structures by X-ray diffraction (Subramony, J. A.; Lovell, S.; Kahr, B. Chem. Mater. 1998, 10, 2053−2057). Here, using micro-Raman spectroscopy, we have deconvoluted the signals of the polycrystalline and crystalline domains, showing that the inescapable pyro- and metaphosphate dehydration products are localized in the polycrystalline material. Those debating whether the transformations are genuine structural phase transformations or are merely dehydration reactions can all be vindicated in certain parts of any one sample.

Stress-induced phase and structural changes in KDP crystals

“…The liquid phase and six solid phases I, II, II 0 , III, IV and V were determined by differential thermal analyses [9] at pressures up to 4 GPa and temperatures up to 450°C. Later, X-ray [10][11][12][13], neutron diffraction [14,15], Raman [16] and theoretical [17] studies revealed a rich phase diagram of KDP.…”

Distribution of metallic ions in a single KDP crystal grown from aqueous solution

“…Colored inorganic crystals by organic compounds were reviewed by Kahr et al [11]. The crystal structure of colored crystals has been widely studied [12][13][14][15]. Operational studies of colored crystals have only been systematically reported as a function of supersaturation and ion concentration [16,17].…”

Synergy of organic dyes for KDP crystal growth

“…Recently, the combination of inorganic crystals and organic dye was reviewed by Kahr et al [12] Dye is a precise habit modifier for some inorganic crystals. The coloring hourglass crystals were investigated [13][14][15][16], and the crystal structure of the coloring crystals has been widely studied [17][18][19][20]. However, operational studies of coloring crystals by dye have rarely been reported even though the operative variables of crystal growth were supersaturation and dye concentration only.…”