Variations of phase transition temperature and enthalpy in the systems Na₂Mo_1−xW_xO₄and Na₂Mo_1−yS_yO₄

Abstract

Abstract The samples in two material systems, Na2Mo1− x W x O4 and Na2Mo1− y S y O4, were prepared by using conventional solid reactions and characterized by X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), and difference scanning calorimetry (DSC). The XRD and EDX data indicated that all the samples in both systems were in the solid solution range. The DSC data indicated that in the system Na2Mo1− x W x O4, the solid–solid transition temperatures increased and in the system Na2Mo1− y S y O4, the solid–solid transition temperatures decreased. The total enthalpy (ΔH total) of the solid–solid transitions in the system Na2Mo1− x W x O4, decreased much less than that in the system Na2Mo1− y S y O4. This is probably because similar to Na2MoO4, the solid–solid transition of Na2WO4 has relatively large ΔH total, but Na2SO4 has much smaller solid–solid transition enthalpy. In order to modify the transition temperatures of Na2MoO4 and also to keep its relatively large ΔH total, it is necessary to choose a doping material with large ΔH total. Keywords: sodium molybdatephase transitiondoping effectenergy storage Acknowledgements We are thankful for the financial support from the National Nature Science Foundation of China (nos 20821091 and 20423005) and the National Basic Research Program of China (no. 2009CB939901).