Anomalous Behavior of Thermal Expansion in Orthorhombic NaCN

Abstract

The orthorhombic phase (D_2h²⁵) of NaCN has the distorted structure (monoclinic cell with a=c, β≠90°) of the higher temperature phase (NaCl-type cubic). The temperature dependences of lattice constants a, b and β are measured by X-ray diffraction method. Anomalous behaviors of thermal expansions of a, b as well as β are observed toward the orthorhombic-cubic transition of first order. The unit cell volume, however, does not exhibit anomalous expansion.