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After as-grown Na2SO4 (V) crystal is transformed to high-temperature phase (I), the transition sequence is I II III on cooling and III I on reheating scan. The intermediate phase II occurs within a very narrow temperature range of 2–3 °C and the transition temperature of II III has been known to be much reduced during subsequent cooling scans. Here, we found that all the transitions I II III as well as III I depend greatly on the thermal prehistory. This is possibly related to an incompleteness of the transition from phase V to I near 240 °C. We also found that if the Na2SO4 (I), which is just transformed from the phase V, is heated above 600 °C, then all the peculiarities on transitions surprisingly disappear. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) |
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