Order-Disorder Phase Transitions in KNO2 , CsNO2, and TlNO2 crystals: A Molecular Dynamics Study

The order-disorder phase transitions of KNO2 , CsNO2, and TlNO2 have been studied using parameter-free molecular dynamics simulation. It is found that the phase transitions in nitrites investigated are driven by the rotations of the NO2 2 ions about different axes together with displacements of cations and anions. We successfully reproduce the high-temperature phases of these nitrites, i.e., the NaCl-like structure for KNO2 and CsCl-like structure for Cs(Tl)NO2. Based on the investigation of the radial distribution function of the cations and anions, we explain why KNO2 and Cs(Tl)NO2 form quite different low-temperature phases