Room-temperature and low-temperature (10 K) Raman spectra of a single crystal NaH,PO, were obtained for various polarizations. The polarization characteristics of the Raman spectra remained unchanged throughout the whole temperature range studied. This confirms that there is no phase transition in this crystal at least down to 10 K. High-frequency H modes showed the well known ABC-type three-band structure and correlated with 0-H --* 0 bond lengtb.

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Double freezing curves of oxygen have been obtained in a cooling process with a rate of less than 40 mK/min. The plateaus of these double freezing curves show differences in temperature and width. The cause of the observed double freezing curve is presumably redistribution of impurities into relatively pure and impure regions by transportation during the slow cooling process. This separation is observed in the melting curve of oxygen using both continuous and pulse heating methods. We note the importance of impurity redistribution on the accuracy of the temperature measurement and the realization of the triple point of oxygen.