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Li2B4O7 crystal structure in anharmonic approximation at 20, 200, 400 and 500 °C.

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Title: Li2B4O7 crystal structure in anharmonic approximation at 20, 200, 400 and 500 °C.
Authors: Sennova, Natalia1 sennatalia@yandex.ru, Bubnova, Rimma2, Shepelev, Jurii2, Filatov, Stanislav1, Yakovleva, Olga3
Source: Journal of Alloys & Compounds. Jan2007, Vol. 428 Issue 1/2, p290-296. 7p.
Subjects: Lithium, Oxygen, Boron, Vibration (Mechanics)
Abstract: Li2B4O7 crystal structure was studied at elevated temperatures and refined in anharmonic approximation: 20 °C, a = 9.475(3), c = 10.283(6) Å, 883 F(h k l), R = 0.015; 200 °C, a = 9.501(3), c = 10.275(6) Å, 826 F(h k l), R = 0.021; 400 °C, a = 9.535(3), c = 10.295(8) Å, 809 F(h k l), R = 0.022; and 500 °C, a = 9.550(3), c = 10.295(6) Å, 779 F(h k l), R = 0.029. B—O bond lengths were corrected in a view of O and B atomic vibrations. Refinement of anharmonic components of atomic temperature factors has revealed high asymmetry of Li thermal vibrations. The behaviour of tetraborate groups was studied. A stability of rigid B—O groups configuration was indicated, as in the case of β—CsB5O8, LiB3O5 and β-Na2B8O13, studied by us earlier. The boron–oxygen framework expands as a three-dimensional hinge; B—O—B and O—B—O angles inside tetraborate groups practically do not change, while B1—O1—B2 angles between the groups increase to 1.6° on heating up to 500 °C due to O1 atoms shifts letting Li atom to fall through oxygen atoms along c-axis causing the contraction in this direction. [Copyright &y& Elsevier]
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Abstract:Li2B4O7 crystal structure was studied at elevated temperatures and refined in anharmonic approximation: 20 °C, a = 9.475(3), c = 10.283(6) Å, 883 F(h k l), R = 0.015; 200 °C, a = 9.501(3), c = 10.275(6) Å, 826 F(h k l), R = 0.021; 400 °C, a = 9.535(3), c = 10.295(8) Å, 809 F(h k l), R = 0.022; and 500 °C, a = 9.550(3), c = 10.295(6) Å, 779 F(h k l), R = 0.029. B—O bond lengths were corrected in a view of O and B atomic vibrations. Refinement of anharmonic components of atomic temperature factors has revealed high asymmetry of Li thermal vibrations. The behaviour of tetraborate groups was studied. A stability of rigid B—O groups configuration was indicated, as in the case of β—CsB5O8, LiB3O5 and β-Na2B8O13, studied by us earlier. The boron–oxygen framework expands as a three-dimensional hinge; B—O—B and O—B—O angles inside tetraborate groups practically do not change, while B1—O1—B2 angles between the groups increase to 1.6° on heating up to 500 °C due to O1 atoms shifts letting Li atom to fall through oxygen atoms along c-axis causing the contraction in this direction. [Copyright &y& Elsevier]
ISSN:09258388
DOI:10.1016/j.jallcom.2006.03.049