Temperature‐dependent Changes of the Crystal Structure of Li₂B₄O₇

Abstract

Abstract The crystal structure of Li 2 B 4 O 7 was studied by single crystal X‐ray diffraction whilst the substance was cooled down from room temperature to −150 °C. The title compound crystallizes in the tetragonal, non‐centrosymmetric space group I 4 1 cd (no. 110), a = 9.475(5) Å (r.t.), c = 10.283(6) Å (r.t.), R values for seven different data sets vary from 2.6 to 2.9 %. Low‐temperature single crystal examinations were combined with low‐temperature powder X‐ray diffraction experiments (−189 – +27 °C). The results are discussed in comparison with data earlier obtained at high temperatures (20 – 500 °C). No phase transitions or abrupt changes of the crystal structure were observed. The coordination sphere of the lithium ions is that of a distorted tetrahedron and remains almost unchanged, although the coordination number of the lithium ions decreases slightly with rising temperature, similarly to what was found for LiB 3 O 5 . An expected rigidity of the boron‐oxygen groups was confirmed. The thermal deformations of the [B 4 O 7 ] 2− framework occur according to the hinge mechanism. This indicates that the LiO 4 chains change their winding on cooling, which leads to deformations along c .