TY - JOUR

T1 - Unexpected dielectric response and relaxation dynamics of NaBa12(BO3)7F4 crystals

AU - Molokov, Anton Yu

AU - Koroleva, Ekaterina Yu

AU - Vakhrushev, Sergey B.

AU - Vakulenko, Alexander F.

AU - Bekker, Tatyana B.

AU - Davydov, Alexey V.

AU - Rashchenko, Sergey V.

AU - Vishnevskiy, Andrey V.

N1 - This work was supported by the Russian Science Foundation, grant № 24-19-00252, https://www.rscf.ru/project/24-19-00252/. Dielectric studies were carried out on the equipment of the Scientific and Educational Center "Physics of Nanocomposite Materials" of Peter the Great St. Petersburg Polytechnic University. Equipment used for cryogenic X-ray diffraction measurements is supported by the state assignment of Sobolev Institute of Geology and Mineralogy SB RAS of the Ministry of Science and Higher Education of the Russian Federation (State record number: FWZN-2026-0014).

PY - 2026/6

Y1 - 2026/6

N2 - The dielectric properties of two deep-purple "antizeolite" borate crystals, NaBa12(BO3)7F4 (NBBF-1 and NBBF-2), synthesized from slightly different high-temperature solution compositions, were investigated. Both crystals possess Ba12(BO3)66+ framework with channels extending along the z-axis. They exhibit a sodium deficiency of approximately 10 % and display a deep purple color, despite the absence of any chromophore ions. The dielectric responses were measured both parallel (||) and perpendicular (⟂) to the z-axis. In NBBF-1 || z, the maximum permittivity (ε′) appears near 290 K, reaching ε′ ≈ 370 at 0.1 Hz, whereas NBBF-2 || z exhibits a similar but lower temperature permittivity peak. No dielectric anomalies are detected in the NBBF ⟂ z samples, where ε′ remains below 20 and is in accordance with the typical borate behavior. Relaxation dynamics in NBBF || z is attributed to the dynamics of polar defects, and the corresponding relaxation process is identified. In NBBF-1, ferroelectric hysteresis loops are observed at 270 K, which suggests that the polar defect system induces weak ferroelectricity in the crystal. These results establish NaBa12(BO3)7F4 as the first high-permittivity ferroelectric borate, offering insights into defect-driven dielectric phenomena.

AB - The dielectric properties of two deep-purple "antizeolite" borate crystals, NaBa12(BO3)7F4 (NBBF-1 and NBBF-2), synthesized from slightly different high-temperature solution compositions, were investigated. Both crystals possess Ba12(BO3)66+ framework with channels extending along the z-axis. They exhibit a sodium deficiency of approximately 10 % and display a deep purple color, despite the absence of any chromophore ions. The dielectric responses were measured both parallel (||) and perpendicular (⟂) to the z-axis. In NBBF-1 || z, the maximum permittivity (ε′) appears near 290 K, reaching ε′ ≈ 370 at 0.1 Hz, whereas NBBF-2 || z exhibits a similar but lower temperature permittivity peak. No dielectric anomalies are detected in the NBBF ⟂ z samples, where ε′ remains below 20 and is in accordance with the typical borate behavior. Relaxation dynamics in NBBF || z is attributed to the dynamics of polar defects, and the corresponding relaxation process is identified. In NBBF-1, ferroelectric hysteresis loops are observed at 270 K, which suggests that the polar defect system induces weak ferroelectricity in the crystal. These results establish NaBa12(BO3)7F4 as the first high-permittivity ferroelectric borate, offering insights into defect-driven dielectric phenomena.

KW - Borate crystals

KW - Dielectric spectroscopy

KW - Dipole defects

KW - Relaxation processes

UR - https://www.scopus.com/pages/publications/105031006336

UR - https://www.mendeley.com/catalogue/f6685c1e-e09c-3a77-aea2-d30e0c310bae/

U2 - 10.1016/j.cjph.2026.01.027

DO - 10.1016/j.cjph.2026.01.027

M3 - Article

VL - 101

SP - 196

EP - 204

JO - Chinese Journal of Physics

JF - Chinese Journal of Physics

SN - 0577-9073

ER -