ANISOTROPIC THERMAL EXPANSION OF POTASSIUM NITRATE CRYSTAL

Anisotropic thermal expansion of potassium nitrate crystal has been studied from - 177°C up to 325°C by the X-ray diffraction method. The values of lattice constants, thermal expansion coefficients and densities have been given at sixteen temperatures. The anisotropic temperature factors for phase II have been determined at - 177°, 30° and 122.5°C. It was recognized that y component of the atomic co-ordinate of NO_3^- ions, which are oriented perpendicular to b axis, has rather large temperature dependence. Anisotropic expansion and thermal motions of atoms in potassium nitrate are discussed qualitatively in relation to the crystal structure