Intermolecular structure around lithium monovalent cations and nitrogen atoms in molten LiNO₃

Abstract

Abstract Time of flight neutron diffraction measurements have been carried out for five LiNO3 melts by changing the isotopic composition of either the Li or the N nucleus. We have determined the intramolecular distances and root mean square displacements of NO- 3 in the molten state: r NO = 1·251 + 0·004 Å, r OO = 2·15 + 0·01 Å, l NO = 0·045 + 0·003 Å, and l OO = 0·073 ± 0·006 Å. Here we used a least squares fit to the intramolecular interference terms for 6,7Li14NO3 and 6,7Li15NO3 associated with a zero coherent scattering length of Li. The isotopic difference method was used to determine the distribution functions [Gbar] Li(r) and [Gbar] N(r) around Li+ and N, and intermolecular partial pair distribution functions g LiN(r), g LiO(r), g NN(r), g NO(r) and g OO(r). The nearest neighbour distances were: r(LiO) = 2·1 ± 0·1 Å, r(LiN) = 2·7 ± 0·1 Å, and r(NN) = 4·8 ± 0·2 Å, r(NO) = 3·9 ± 0·2 Å, and r(OO) = 3·2 ± 0·2 Å. We have proposed a perspective view of most probable local structure around Li+: a lithium monovalent cation is surrounded tetrahedrally by four nitrate ions, and one oxygen atom in each of these four NO- 3 ions faces towards Li+, where the four nearest neighbour oxygen atoms form a tetrahedron around Li+. It is of much interest that the most probable local structure of molten LiNO3 is quite different from the structure of crystalline LiNO3.