TY - JOUR

T1 - Thermal behaviour of the rigid boron-oxygen groups in the α-Na2B8O13 crystal structure

AU - Bubnova, R. S.

AU - Shepelev, Ju F.

AU - Sennovan, N. A.

AU - Filatov, S. K.

PY - 2002/1/1

Y1 - 2002/1/1

N2 - The crystal structure of the α-Na2B8O13 stable modification has been refined by single crystal X-ray diffraction at 293, 573 and 773 K. The compound is monoclinic, P21/a space group, unit-cell parameters at 273 K are: a = 6.507(3), b = 17.796(8), c = 8.377(5) Å, β = 96.60(4)°, Z = 4. The structure contains two interlocking boron-oxygen frameworks, each of them consisting of alternating single and double rings composed of two triangles and a tetrahedron so called triborate and pentaborate groups. Two non-equivalent sodium atoms linking two frameworks are coordinated by 8 oxygens. They are connected into finite chains consisting of four NaO8 polyhedra by sharing oxygen edges. The α-Na2B8O13 thermal expansion investigated by high temperature powder X-ray diffraction has sharply anisotropic character including negative thermal expansion: the coefficients of a thermal expansion tensor in temperature region 273-1000 K are α11 = 55-0.042 · (273 + t) α22=11, α33 = 15 + 0.032 · (273 + t), (x 10-6 K-1), μ = (cα33) = 42°. That high anisotropy is caused by anisotropic thermal vibrations of the Na atoms. Under heating a high stability of the B-O rigid groups and a weak contraction of some B-O bond lengths were revealed. In response to anisotropic thermal behaviour of Na atoms rigid B-O groups of the anion framework rotate relative to each other as a three-dimensional hinge.

AB - The crystal structure of the α-Na2B8O13 stable modification has been refined by single crystal X-ray diffraction at 293, 573 and 773 K. The compound is monoclinic, P21/a space group, unit-cell parameters at 273 K are: a = 6.507(3), b = 17.796(8), c = 8.377(5) Å, β = 96.60(4)°, Z = 4. The structure contains two interlocking boron-oxygen frameworks, each of them consisting of alternating single and double rings composed of two triangles and a tetrahedron so called triborate and pentaborate groups. Two non-equivalent sodium atoms linking two frameworks are coordinated by 8 oxygens. They are connected into finite chains consisting of four NaO8 polyhedra by sharing oxygen edges. The α-Na2B8O13 thermal expansion investigated by high temperature powder X-ray diffraction has sharply anisotropic character including negative thermal expansion: the coefficients of a thermal expansion tensor in temperature region 273-1000 K are α11 = 55-0.042 · (273 + t) α22=11, α33 = 15 + 0.032 · (273 + t), (x 10-6 K-1), μ = (cα33) = 42°. That high anisotropy is caused by anisotropic thermal vibrations of the Na atoms. Under heating a high stability of the B-O rigid groups and a weak contraction of some B-O bond lengths were revealed. In response to anisotropic thermal behaviour of Na atoms rigid B-O groups of the anion framework rotate relative to each other as a three-dimensional hinge.

UR - http://www.scopus.com/inward/record.url?scp=0036397001&partnerID=8YFLogxK

U2 - 10.1524/zkri.217.9.444.22881

DO - 10.1524/zkri.217.9.444.22881

M3 - Article

AN - SCOPUS:0036397001

VL - 217

SP - 444

EP - 450

JO - Zeitschfrift fur Kristallographie

JF - Zeitschfrift fur Kristallographie

SN - 0044-2968

IS - 9

ER -