Thermal behavior of polymorphic modifications of LuBO3

Y. P. Biryukov, R. S. Bubnova, M. G. Krzhizhanovskaya, S. K. Filatov, A. V. Povolotskiy, V. L. Ugolkov

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Abstract

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.

Original languageEnglish
Article number106061
JournalSolid State Sciences
Volume99
Early online date2 Nov 2019
DOIs
Publication statusPublished - Jan 2020

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Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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