TY - JOUR

T1 - BaF2–B2O3 Fluorooxoborates: Insights into Electronic Structure, Mechanical Properties, and High-Pressure Stability

AU - Sagatov, Nursultan E.

AU - Bekker, Tatyana B.

N1 - This work was supported by the Russian Science Foundation, grant No 24-19-00252, https://www.rscf.ru/project/24-19-00252/. The calculations were performed using computational resources provided by the state assignment of IGM SB RAS (FWZN-2026-0014).

PY - 2026/7/23

Y1 - 2026/7/23

N2 - Barium fluorooxoborates have recently emerged as promising candidates for deep-ultraviolet optical materials, yet their electronic, vibrational, mechanical properties, and high-pressure behavior remain largely unexplored. In this work, we systematically investigate the thermodynamic stability, vibrational properties, electronic structure, and mechanical response of three intermediate compounds in the BaF2–B2O3 system, BaB2O3F2, BaB4O6F2, and BaB8O12F2, under hydrostatic pressures from 0 to 10 GPa using density functional theory. Convex hull analysis shows that BaB2O3F2 is thermodynamically stable across the entire pressure range, whereas BaB4O6F2 and BaB8O12F2 become metastable above ∼1.5 GPa, decomposing into BaB2O3F2 and B2O3. Phonon calculations confirm dynamic stability at ambient pressure, and the Raman spectra are calculated and described. Electronic structure calculations with the HSE06 hybrid functional yield for BaB2O3F2, BaB4O6F2, and BaB8O12F2 large indirect band gaps of 8.55, 8.18, and 8.36 eV, respectively, which further increase under compression. Mechanical analysis indicates that all compounds satisfy the Born stability criteria. BaB2O3F2 exhibits the highest stiffness and Vickers hardness, surpassing conventional nonlinear optical crystals such as β-BBO and KDP. BaB8O12F2 offers balanced mechanical performance, while BaB4O6F2 is significantly softer. Notably, BaB8O12F2 remains dynamically and mechanically stable up to at least 10 GPa in a metastable state, whereas BaB4O6F2 loses stability above ∼4 GPa. Collectively, these results establish the first pressure–composition phase diagram of the BaF2–B2O3 system and demonstrate that barium fluorooxoborates combine deep-UV transparency with superior mechanical robustness, making them attractive for optical applications under extreme conditions.

AB - Barium fluorooxoborates have recently emerged as promising candidates for deep-ultraviolet optical materials, yet their electronic, vibrational, mechanical properties, and high-pressure behavior remain largely unexplored. In this work, we systematically investigate the thermodynamic stability, vibrational properties, electronic structure, and mechanical response of three intermediate compounds in the BaF2–B2O3 system, BaB2O3F2, BaB4O6F2, and BaB8O12F2, under hydrostatic pressures from 0 to 10 GPa using density functional theory. Convex hull analysis shows that BaB2O3F2 is thermodynamically stable across the entire pressure range, whereas BaB4O6F2 and BaB8O12F2 become metastable above ∼1.5 GPa, decomposing into BaB2O3F2 and B2O3. Phonon calculations confirm dynamic stability at ambient pressure, and the Raman spectra are calculated and described. Electronic structure calculations with the HSE06 hybrid functional yield for BaB2O3F2, BaB4O6F2, and BaB8O12F2 large indirect band gaps of 8.55, 8.18, and 8.36 eV, respectively, which further increase under compression. Mechanical analysis indicates that all compounds satisfy the Born stability criteria. BaB2O3F2 exhibits the highest stiffness and Vickers hardness, surpassing conventional nonlinear optical crystals such as β-BBO and KDP. BaB8O12F2 offers balanced mechanical performance, while BaB4O6F2 is significantly softer. Notably, BaB8O12F2 remains dynamically and mechanically stable up to at least 10 GPa in a metastable state, whereas BaB4O6F2 loses stability above ∼4 GPa. Collectively, these results establish the first pressure–composition phase diagram of the BaF2–B2O3 system and demonstrate that barium fluorooxoborates combine deep-UV transparency with superior mechanical robustness, making them attractive for optical applications under extreme conditions.

UR - https://www.scopus.com/pages/publications/105045575919

UR - https://www.mendeley.com/catalogue/d73784ce-67c9-30f3-9bf2-d9ed495c85b6/

U2 - 10.1021/acs.jpcc.6c03273

DO - 10.1021/acs.jpcc.6c03273

M3 - Article

VL - 130

SP - 10453

EP - 10463

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 29

ER -