TY - JOUR

T1 - High-Pressure Synthesis, Electronic Properties, and Raman Spectroscopy of Barium Tetraborate BaB4O7Polymorphs

AU - Bekker, Tatyana B.

AU - Sagatov, Nursultan E.

AU - Podborodnikov, Ivan V.

AU - Shatskiy, A. F.

AU - Rashchenko, Sergey

AU - Goryainov, Sergey V.

AU - Davydov, Alexey

AU - Litasov, Konstantin D.

N1 - Funding Information: This work was supported by the Russian Science Foundation, grant No. 21-19-00097. We thank the Information and Computing Center of Novosibirsk State University for providing access to the cluster computational resources. Publisher Copyright: ©

PY - 2022/5/4

Y1 - 2022/5/4

N2 - The synthesis of high-pressure modification of barium tetraborate β-BaB4O7 has been carried out at 3 GPa and 1000 °C in a DIA-type apparatus. Single-crystal X-ray analysis shows that β-BaB4O7 crystallizes in a centrosymmetric group (Pnam (#62), a = 9.0029(3) Å, b = 4.3006(7) Å, c = 10.9795(8) Å, Z = 4). The density of the β-BaB4O7 phase increases by 22% relative to the ambient-pressure α-BaB4O7 phase. The P-T diagrams for the α- and β-BaB4O7 phases have been calculated. The dynamic stability of β-BaB4O7 at ambient pressure was confirmed by the absence of imaginary modes in the phonon spectra. The band gap values obtained using the HSE06 hybrid functional are 6.821 and 8.075 eV for α- and β-BaB4O7 phases, respectively, with indirect transitions. The value of 8.075 eV indicates that β-BaB4O7 can transmit to the deep-UV region. For the first time, the Raman spectra of the α- and β-BaB4O7 phases have been studied by both experimental and numerical methods. The vasp_raman.py code was used to calculate the polarizability tensors for each crystal mode. The assignment of vibrations of cations, interconnected triangle, and/or tetrahedral groups (BO3 and BO4) of both modifications was carried out by comparing the experimental and ab initio calculated spectra and the result is in agreement with the interpretation developed for borates, aluminosilicates, and carbonates.

AB - The synthesis of high-pressure modification of barium tetraborate β-BaB4O7 has been carried out at 3 GPa and 1000 °C in a DIA-type apparatus. Single-crystal X-ray analysis shows that β-BaB4O7 crystallizes in a centrosymmetric group (Pnam (#62), a = 9.0029(3) Å, b = 4.3006(7) Å, c = 10.9795(8) Å, Z = 4). The density of the β-BaB4O7 phase increases by 22% relative to the ambient-pressure α-BaB4O7 phase. The P-T diagrams for the α- and β-BaB4O7 phases have been calculated. The dynamic stability of β-BaB4O7 at ambient pressure was confirmed by the absence of imaginary modes in the phonon spectra. The band gap values obtained using the HSE06 hybrid functional are 6.821 and 8.075 eV for α- and β-BaB4O7 phases, respectively, with indirect transitions. The value of 8.075 eV indicates that β-BaB4O7 can transmit to the deep-UV region. For the first time, the Raman spectra of the α- and β-BaB4O7 phases have been studied by both experimental and numerical methods. The vasp_raman.py code was used to calculate the polarizability tensors for each crystal mode. The assignment of vibrations of cations, interconnected triangle, and/or tetrahedral groups (BO3 and BO4) of both modifications was carried out by comparing the experimental and ab initio calculated spectra and the result is in agreement with the interpretation developed for borates, aluminosilicates, and carbonates.

UR - http://www.scopus.com/inward/record.url?scp=85129003413&partnerID=8YFLogxK

U2 - 10.1021/acs.cgd.2c00211

DO - 10.1021/acs.cgd.2c00211

M3 - Article

AN - SCOPUS:85129003413

VL - 22

SP - 3405

EP - 3412

JO - Crystal Growth and Design

JF - Crystal Growth and Design

SN - 1528-7483

IS - 5

ER -