A neutron diffraction determination of the crystal structure of α-phase potassium nitrate at 25 degrees C and 100 degrees C

14N and 39K Nuclear Quadrupole Coupüng in KNO3

“…The asymmetry parameter, however, is nonzero in KN0 3 , where the N0 3 group has less than trigonal symmetry. In a neutron diffraction study, Nimmo and Lucas located one of the N0 2 planes in the molecule parallel to the (a, b) plane of the crystal and the other O atom slightly displaced from it [1]. The small separation of the curves in Fig.…”

“…Potassium nitrate at room temperature (a phase) has the aragonite structure which is orthorhombic, space group Pmcn, Z = 4 [1]. A feature of this assignment is that the crystallographic (b, c) plane containing the potassium and nitrogen atoms is a mirror plane, so that the a-axis of the crystal must be a principal axis of the electric field gradient tensor at both nuclei.…”

Phase Transition of KNO3 Monitored by Synchrotron X-ray Powder Diffraction

“…The crystal structure of ~-KNO3 was reported by Nimmo & Lucas (1973) and the structures of/3-KNO3 and 3,-KNO3 were reported by Nimmo & Lucas (1976), and the relations between the three structures have been established. The phase transitions of KNO3 were also investigated in first-principles simulation studies (Lu & Hardy, 1991) and the probable crystallographic paths for the thermal phase transitions in KNO3 were investigated by Swaminathan & Srinivasan (1975).…”

Orientations and twinning in the structural transformation aragonite-type to calcite-like in potassium nitrate crystals

“…This structure change is well known in calcium carbonate: a very similar transformation occurs in potassium nitrate, KNO3. Below 128°C potassium nitrate has a closely pseudo-hexagonal aragonite structure (II), space group Pmcn, Z--4 (Edwards, 1931;Nimmo & * Present address: South Australian Institute of Technology, Pooraka, SA 5098, Australia. Lucas, 1973), and at higher temperatures the highNaNO 3 structure (I), space group R3m, in which there is considerable thermal oscillation of the NOj ions (Shinnaka, 1962;Stromme, 1969).…”

“…Below 128°C potassium nitrate has a closely pseudo-hexagonal aragonite structure (II), space group Pmcn, Z--4 (Edwards, 1931;Nimmo & * Present address: South Australian Institute of Technology, Pooraka, SA 5098, Australia. Lucas, 1973), and at higher temperatures the highNaNO 3 structure (I), space group R3m, in which there is considerable thermal oscillation of the NOj ions (Shinnaka, 1962;Stromme, 1969). Though this differs from calcite in the relative mean orientations of the anions the difference must become less significant at higher temperatures because of the increased amplitude of oscillation of the CO 2-ions.…”