Temperature‐dependent Changes of the Crystal Structure of Li₂B₄O₇

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 Ϫ150°C. The title compound crystallizes in the tetragonal, non-centrosymmetric space group I 4 1 cd (no. 110), a ϭ 9.475(5) Å (r.t.), c ϭ 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 (Ϫ189 Ϫ ϩ27°C). The results are discussed in comparison with data earlier obtained at high temperatures (20 Ϫ 500°C). No phase transitions or abrupt changes of the crystal structure were observed. The coordination 2601 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 boronoxygen groups was confirmed. The thermal deformations of the [B 4 O 7 ] 2Ϫ 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.

Borates—Crystal Structures of Prospective Nonlinear Optical Materials: High Anisotropy of the Thermal Expansion Caused by Anharmonic Atomic Vibrations

“…Like silicates [73], the borates under study (see Section 4) show a weak contraction of the majority of individual and average strong and short B-O bond lengths when temperature changes, as it was observed in previously studied α-Na 2 B 8 O 13 [46], LiB 3 O 5 (20-400) [47], α-CsB 5 O 8 [48], and Li 2 B 4 O 7 [50,51]. The results of these studies were summarized in [26].…”

“…The thermal invariability of rigid groups has been proven by single crystal HTXRD and LTXRD studies (HT, high temperature; LT low temperature) of about a dozen of borates [46][47][48][49][50][51][52][53][54][55][56][57][58], etc. These results have been summarized in [26,34,42,43] and are briefly described here.…”

Electron and hole traps in Ag-doped lithium tetraborate (Li2B4O7) crystals

“…Then, the crystal was returned to 30 K in the microwave cavity, and the EPR spectra were again recorded. This procedure of warming the sample to successively higher temperatures was repeated in 25 C steps from 50 to 200 C. After each anneal, the sample was returned to 30 K where the intensities of the EPR signals were monitored. The data in Fig.…”

Low-temperature crystal structure, specific heat, and dielectric properties of lithium tetraborate Li2B4O7

“…23 it is defined that c lattice parameter shows a minima on its temperature evolution around 500 K. Recent high-resolution powder diffraction studies using synchrotron radiation 24 performed on Li 2 B 4 O 7 with natural isotope composition showed lattice contraction in ͓001͔ direction of the lattice, but did not reveal any extrema on thermal dependence of cell volume.…”

“…The Li-O polyhedron can be presented as a distorted tetrahedron built on O1, O2, O3a, and O3b, whereas at higher temperatures it can be better defined as a distorted bipyramid 23 built on O1, O2, O3a, O3b, and O4. The Li-O1 interatomic distance almost linearly increases upon heating from 2.130͑2͒ Å at 3.4 K to 2.183͑4͒ Å at 268 K. The Li-O2 bond length displays linear increase as well ͓1.950͑1͒ Å at 3.4 K and 1.967͑2͒ at 268 K͔ but with smaller magnitude of thermal elongation.…”