TY - JOUR

T1 - Thermal, Structural, and Transport Properties of Solid Solutions Based on Organic Ionic Plastic Crystals (C 3 H 7 ) 4 NBF 4 and (C 4 H 9 ) 4 NBF 4

AU - Stebnitskii, Ivan

AU - Mateyshina, Yulia

AU - Polovyanenko, Dmitriy

AU - Uvarov, Nikolai

N1 - Thermal, Structural, and Transport Properties of Solid Solutions Based on Organic Ionic Plastic Crystals (C3H7) 4NBF4 and (C4H9) 4NBF4 // Journal of Physical Chemistry C. - 2025. - Т. 129 - № 48. - С. 21477-21485. DOI: 10.1021/acs.jpcc.5c06036. This research was funded by the Ministry of Science and Higher Education of the Russian Federation (project numbers 121032500065-5). Authors would like to acknowledge the Multi-Access Chemical Research Center SB RAS for spectral and analytical measurements.

PY - 2025/11/21

Y1 - 2025/11/21

N2 - Organic ionic plastic crystals (OIPCs) are promising candidates for solid electrolytes due to their favorable properties, including incombustibility, plasticity, and high electrochemical stability. However, the ionic conductivity of many OIPCs remains insufficient for practical applications. Isovalent substitution represents a potential strategy for enhancing the transport properties. This study examines the effects of isovalent substitution with larger cations on the thermal, structural, and transport properties of a binary system based on tetrapropylammonium tetrafluoroborate (Pr4NBF4) and tetrabutylammonium tetrafluoroborate (Bu4NBF4). In the Pr4NBF4 – Bu4NBF4 system, the temperature of the polymorphic phase transition (II → I) decreased with an increasing dopant concentration. The melting temperature also decreased monotonically, from 247 to 163 °C, as the fraction of Bu4NBF4 increased. Above the II → I transition temperature, all compositions adopted a cubic phase (space group P4̅3n), isomorphic to the high-temperature phase of the pure salts, with a linear expansion of the cell parameter as the Bu4NBF4 content increased. Thermal and X–ray diffraction analyses confirmed the formation of a continuous solid solution across the entire composition range. Replacement of Pr4N+ with the large Bu4N+ cation increased ionic conductivity from 1.5 × 10–9 S × cm–1 (pure Pr4NBF4) to 6.3 × 10–7 S × cm–1 (pure Bu4NBF4) at 140 °C, which is explained by a decrease in the enthalpy of defect formation. Notably, two conductivity maxima were observed near 10 and 95 mol % Bu4NBF4, deviating from the overall trend. These enhancements are likely due to uncompensated microdeformations around impurity ions, which reduce the migration enthalpy. The study demonstrates the possibility of controlling both the thermal and transport properties of organic ionic plastic crystals through isovalent doping.

AB - Organic ionic plastic crystals (OIPCs) are promising candidates for solid electrolytes due to their favorable properties, including incombustibility, plasticity, and high electrochemical stability. However, the ionic conductivity of many OIPCs remains insufficient for practical applications. Isovalent substitution represents a potential strategy for enhancing the transport properties. This study examines the effects of isovalent substitution with larger cations on the thermal, structural, and transport properties of a binary system based on tetrapropylammonium tetrafluoroborate (Pr4NBF4) and tetrabutylammonium tetrafluoroborate (Bu4NBF4). In the Pr4NBF4 – Bu4NBF4 system, the temperature of the polymorphic phase transition (II → I) decreased with an increasing dopant concentration. The melting temperature also decreased monotonically, from 247 to 163 °C, as the fraction of Bu4NBF4 increased. Above the II → I transition temperature, all compositions adopted a cubic phase (space group P4̅3n), isomorphic to the high-temperature phase of the pure salts, with a linear expansion of the cell parameter as the Bu4NBF4 content increased. Thermal and X–ray diffraction analyses confirmed the formation of a continuous solid solution across the entire composition range. Replacement of Pr4N+ with the large Bu4N+ cation increased ionic conductivity from 1.5 × 10–9 S × cm–1 (pure Pr4NBF4) to 6.3 × 10–7 S × cm–1 (pure Bu4NBF4) at 140 °C, which is explained by a decrease in the enthalpy of defect formation. Notably, two conductivity maxima were observed near 10 and 95 mol % Bu4NBF4, deviating from the overall trend. These enhancements are likely due to uncompensated microdeformations around impurity ions, which reduce the migration enthalpy. The study demonstrates the possibility of controlling both the thermal and transport properties of organic ionic plastic crystals through isovalent doping.

UR - https://www.scopus.com/pages/publications/105023951039

UR - https://www.mendeley.com/catalogue/112301de-3faf-3a72-b824-015a996a246e/

U2 - 10.1021/acs.jpcc.5c06036

DO - 10.1021/acs.jpcc.5c06036

M3 - Article

VL - 129

SP - 21477

EP - 21485

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 48

ER -