ELECTRICAL AND THERMAL INVESTIGATIONS OF THE PHASE-TRANSITION IN SODIUM-BICARBONATE, NAHCO3

This paper reports on a structural phase transition in sodium hydrogen carbonate, NaHCO3 as revealed by the investigations of some electrica l and thermal parameters. Measurements of d.c. electric conductivity ( sigma) and relative premittivity (epsilon) of polycrystalline samples of NaHCO3 as a function of temperature in the interval 300 < T < 400 K reveal the existence of a structural phase transition around 365 K. D ifferential thermal analysis (DTA) and thermogravimetric analysis (TGA ) were also performed in the same temperature range. The (DTA) results confirm the existence of a structural phase transition at similar or equal to 365 K whereas the (TGA) results show the absence of any actua l loss in weight in the transition temperature region. The data are co rrelated to the crystal structure including the hydrogen bonding syste m.