TY - JOUR

T1 - Thermal behavior of polymorphic modifications of LuBO3

AU - Biryukov, Y. P.

AU - Bubnova, R. S.

AU - Krzhizhanovskaya, M. G.

AU - Filatov, S. K.

AU - Povolotskiy, A. V.

AU - Ugolkov, V. L.

PY - 2020/1

Y1 - 2020/1

N2 - The monoclinic crystal structure of unquenchable phase HT-LuBO3 was refined by the Rietveld method at 1100 °C. It crystallizes in space group C2/c and its structure is composed of the distorted [BO4]5– and [LuO8]13− polyhedra. The [BO4]5– tetrahedra are condensed via two vertices each to form the cyclo-[B3O9]9– anions. The presence of the [BO4]5– units was confirmed by high-temperature Raman spectroscopy at 1100 °C. The thermal behavior of β-, π- and HT-LuBO3 was investigated by high-temperature X-ray powder diffraction (HTXRD) and thermal analysis (TG + DSC). The crystal structure of calcite-type β-LuBO3 expands highly anisotropically. The maximum thermal expansion is along the c axis (αc = 11.69 ‧ 10−6 °C−1 at 20 °C), i.e. perpendicular to the planes of the [BO3]3– triangles. A weak negative expansion occurs in the ab plane (αa = −0.33 ‧ 10−6 °C−1 at 20 °C). The structure of pseudo-wollastonite-type π-LuBO3 expands maximally in the direction that is close to the a axis (α11 = 7.68 ‧ 10−6 °C−1 at 20 °C), where the flexible chains consisting of the edge-sharing [LuO8]13− polyhedra are located. The expansion of HT-LuBO3 is virtually isotropic within the ab plane, where the [B3O9]9– rings are located. The phase transition π- ↔ HT-LuBO3 is reversible and isosymmetric.

AB - The monoclinic crystal structure of unquenchable phase HT-LuBO3 was refined by the Rietveld method at 1100 °C. It crystallizes in space group C2/c and its structure is composed of the distorted [BO4]5– and [LuO8]13− polyhedra. The [BO4]5– tetrahedra are condensed via two vertices each to form the cyclo-[B3O9]9– anions. The presence of the [BO4]5– units was confirmed by high-temperature Raman spectroscopy at 1100 °C. The thermal behavior of β-, π- and HT-LuBO3 was investigated by high-temperature X-ray powder diffraction (HTXRD) and thermal analysis (TG + DSC). The crystal structure of calcite-type β-LuBO3 expands highly anisotropically. The maximum thermal expansion is along the c axis (αc = 11.69 ‧ 10−6 °C−1 at 20 °C), i.e. perpendicular to the planes of the [BO3]3– triangles. A weak negative expansion occurs in the ab plane (αa = −0.33 ‧ 10−6 °C−1 at 20 °C). The structure of pseudo-wollastonite-type π-LuBO3 expands maximally in the direction that is close to the a axis (α11 = 7.68 ‧ 10−6 °C−1 at 20 °C), where the flexible chains consisting of the edge-sharing [LuO8]13− polyhedra are located. The expansion of HT-LuBO3 is virtually isotropic within the ab plane, where the [B3O9]9– rings are located. The phase transition π- ↔ HT-LuBO3 is reversible and isosymmetric.

KW - Crystal structure

KW - High-temperature X-ray powder diffraction (HTXRD)

KW - Lutetium orthoborate

KW - Rietveld refinement

KW - Thermal expansion

UR - http://www.scopus.com/inward/record.url?scp=85075004339&partnerID=8YFLogxK

U2 - 10.1016/j.solidstatesciences.2019.106061

DO - 10.1016/j.solidstatesciences.2019.106061

M3 - Article

AN - SCOPUS:85075004339

VL - 99

JO - Solid State Sciences

JF - Solid State Sciences

SN - 1293-2558

M1 - 106061

ER -