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

Research output


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
Early online date2 Nov 2019
Publication statusPublished - Jan 2020


Scopus subject areas

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

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