Specific heat of ferroelectric NaNO2at low temperatures

Specific-heat measurements on a single crystal (unpoled) of NaN${\mathrm{O}}_2$ from 1.7 to 74 K are reported for the first time. Two non-Debye features are found, similar to previous findings on other ferroelectrics: a $T^{\frac{3}{2}}$ contribution below about 4 K, and a broad maximum in $\frac{C}{T^3}$ at 17 K describable by a single Einstein term of frequency 56.4 ${\mathrm{cm}}^{-1\mathrm{}}$. The Debye temperatures determined in these two regions are 302 and 298 K, respectively. No evidence is found for the mode at 195 ${\mathrm{cm}}^{-1\mathrm{}}$ suggested by recent analyses of low-temperature pyroelectric data on NaN${\mathrm{O}}_2$.