Structural studies of boracites. III. The cubic phase of nickel iodine boracite, Ni3B7O13I, at room temperature

For pt.II see ibid., vol.7, p.3855 (1974). Results are presented for a full three-dimensional structural study of a single-crystal (100) growth sector of pure synthetic Ni 3 B 7 O 13 I. The data were collected with MoK alpha radiation on a four-circle diffractometer out to sin theta / lambda =0.90 AA -1 . The techniques of constrained refinement and significance testing have been used to test carefully the significance of (i) various features of the positional parameters and (ii) the inclusion of parameters to describe third- and fourth-order (anharmonic) terms in the thermal motion of some ions. The final R index was 3.5%. It is concluded that the structure is essentially the same as that previously found for cubic Cr 3 B 7 O 13 Cl.