Temperature-dependent Raman spectra of mixed crystals of NaNO3-KNO3: Evidence for limited solid solutions

The temperature dependence of the Raman spectra of NaNO3-KNO3 was employed to follow structural phase transitions of mixed crystals with different com positions. Solid solutions in the NaNO3 terminal phase behaved like NaNO3 I , solid solutions in the KNO3 terminal phase behaved like KNO3 I and solid solutions in the intermediate phase appeared to be a mixture of NaNO3 I and KNO3 I on the scale of a few tens to hundreds of nanometers. The three dif ferent behaviours of the solid solutions below the solidus suggest that NaN O3-KNO3 might well be regarded as a system with limited solid solutions ins tead of a continuous series of solid solutions, The limited solid solution model seems to be more consistent with the phase diagrams obtained by diffe rential scanning calorimetry. Copyright (C) 1999 John Wiley & Sons, Ltd.