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This paper reports on a structural phase transition in sodium hydrogen carbonate, NaHCO, as revealed by the investigations of some electrical and thermal parameters.Measurements of d.c. electric conductivity (a) and relative premittivity ( E ) of polycrystalline samples of NaHCO, as a function of temperature in the interval 300 c T < 400K 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 r 3 6 5 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.

conductivity (~) and the relative permittivity (~) were accurately measured as a function of temperature in the range 300 < T< 450 K for ammonium oxalate monohydrate (AOX), (NH4)2 C204H20 and potassium oxalate monohydrate (POX), K2C204H20. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) from 300 K up to 520 K were also performed for each compound. The data of the electrical parameters combined with the DTA and/or DSC thermograms suggest the existence ot; a possible change in the electrical conduction at 350 K for AOX and at 355 K for POX. Like most hydrogen-bonded molecules, the charge carriers may be protons and the electrical conduction is therefore protonic. At somewhat higher temperatures, dehydration and/or decomposition takes place in each compound and is reflected as a sudden loss in weight in the TGA plot.

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