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 electrical 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. Differential 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 actual loss in weight in the transition temperature region. The data are correlated to the crystal structure including the hydrogen bonding system.