Ab-initio study of phase transitions in NaNO2 crystals based on band structure calculations

The present investigation is an ab-initio study using CRYSTAL’06 code of the thermally and pressure stimulated phase transitions in NaNO2 crystal using band structure calculations. The paraelectric crystal structure has been represented by the double ferroelectric unit cell with opposite spatial orientations of the main molecular unit NaNO2 in neighboring cells along the polar y-axis. The “total energy – unit cell volume” dependences E(V) for the ferroelectric and paraelectric structures have been found to possess two crossing points. The corresponding dependences of enthalpy H versus pressure P possess crossing points as well, that is in agreement with the pressure induced phase transition at 8.8 GPa and the temperature stimulated ferroelectric–paraelectric phase transition at 437–438 K. The sequence of principal components of the elastic compliance tensor, s11 > s22 > s33, has been found to be the same as the corresponding sequence of thermal linear expansion coefficients, α1 > α2 > α3, of the crystal.