γ-BaB2O4: High-Pressure High-Temperature Polymorph of Barium Borate with Edge-Sharing BO4 Tetrahedra

Tatyana B Bekker; Ivan V Podborodnikov; Nursultan E Sagatov; Anton Shatskiy; Sergey Rashchenko; Dinara N Sagatova; Alexey Davydov; Konstantin D Litasov

doi:10.1021/acs.inorgchem.1c03760

γ-BaB₂O₄: High-Pressure High-Temperature Polymorph of Barium Borate with Edge-Sharing BO₄ Tetrahedra

Inorg Chem. 2022 Jan 31;61(4):2340-2350. doi: 10.1021/acs.inorgchem.1c03760. Epub 2022 Jan 18.

Authors

Tatyana B Bekker^{1

2

3}, Ivan V Podborodnikov^{1

2}, Nursultan E Sagatov^{1

2}, Anton Shatskiy^{1

2}, Sergey Rashchenko^{1

2}, Dinara N Sagatova^{1

2}, Alexey Davydov^{1

2}, Konstantin D Litasov^{4

5}

Affiliations

¹ Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk, Russia.
² Novosibirsk State University, 630090 Novosibirsk, Russia.
³ Novosibirsk State University of Architecture, Design and Arts (NSUADA), 630099 Novosibirsk, Russia.
⁴ Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, 108840 Troitsk Moscow, Russia.
⁵ Fersman Mineralogical Museum, Russian Academy of Sciences, 119071 Moscow, Russia.

PMID: 35040639
DOI: 10.1021/acs.inorgchem.1c03760

Abstract

The α- and β-modifications of barium metaborate are important functional materials used in optoelectronic devices. A new theoretically predicted modification of BaB₂O₄ has been synthesized under conditions of 3 GPa and 900 °C, using the DIA-type apparatus. The new high-pressure modification, γ-BaB₂O₄, crystallizes in a centrosymmetrical group of monoclinic syngony (P2₁/n (#14), a = 4.6392(4) Å, b = 10.2532(14) Å, c = 7.066(1) Å, β = 91.363(10)°, Z = 4). A distinctive feature of the γ-BaB₂O₄ structure is the presence of edge-sharing tetrahedra [B₂O₆] which form infinite double chains _∞[B₄O₄O_8/2] stretching along the a axis. The number of known structural types with the [B₂O₆] group is limited. Phase γ-BaB₂O₄ has the shortest distance between boron atoms of shared tetrahedra among all currently known compounds. The [B₂O₆] group angles are 95.5° and 105.5°. Thermodynamic stability and electronic properties of the γ-BaB₂O₄ modification were studied. The width of the band gap, calculated using the HSE06 functional, is 7.045 eV which implies transparency in the deep-UV region. Experimental and numerical methods which demonstrate a good match were used to the study the Raman spectra of γ-BaB₂O₄ and β-BaB₂O₄ modifications. In the Raman spectra of γ-BaB₂O₄, the most intense band at a frequency of 853 cm^-1 was found to correspond to the symmetric bending mode of the B-O-B-O ring in edge-sharing tetrahedra.