Interfacial Properties of Composites Based on h-BN and c-BN in Function of Temperature–A Molecular Dynamics Study

Boron Nitride (BN) is a material with potential for use in various technological applications and this is due to its unprecedented structural, chemical, thermal, mechanical, optical and electrical properties [1]. Among its various polymorphs, those that have a two-dimensional hexagonal (h-BN) and three-dimensional cubic (c-BN) crystal structure have been the most studied [1-3]. Under normal pressure and temperature conditions, h-BN is more stable than c-BN, however it is possible to cause a c-BN→h-BN phase transition over a wide temperature range, depending on the degree of impurity, grain size and defects in c-BN [4,5]. Recent research has demonstrated that mixing c-BN and h-BN could produce new composites with desirable properties for optoelectronics and thermal energy management applications [6,7]. However, there is still a need for a better understanding of the interfacial interaction between the cubic and hexagonal phases, which can influence the mechanical, thermal and electrical properties of the resulting composite [7]. In this work, using molecular dynamics simulations and the ReaxFF force field, we study the c-BN/h-BN composites under different temperatures in order to evaluate the interfacial interaction between the composite constituents and the possibility of c-BN→h-BN phase transition. Our results demonstrate that the surface termination of the c-BN (whether B or N terminated) is a crucial factor for a phase transition in function of the subjected temperature. The B terminated c-BN surface presents lower energy than the N-terminated one. However, in comparison with h-BN energy, the B terminated c-BN surface presents a lower and N-terminated c-BN surface presents a higher energy than the h-BN. Then, increasing the temperature, the energy of the B terminated c-BN surface becomes closer and closer to the h-BN ones which results in a detachment of it between 500-700K, becoming a h-BN layer. Keeping increasing the temperature, more h-BN layers will be detached from the newly formed B terminated c-BN surface. Then, temperature variations that the c-BN/h-BN composite can suffer in certain applications can impact the proportion between the different phases in relation to the initial one, changing the properties of the composite.<br/><br/>[1] ROY, S. <i>et al.</i>, Adv. Mater. 2021, 33, 2101589.<br/>[2] ZHANG, K.; FENG, Y.; WANG, F.; Yang, Z.; WANG, J, J. Mater. Chem. C 2017, 5, 11992-12022.<br/>[3] VEL, L.; DEMAZEAU, G.; ETOURNEAU, J., Mater. Sci. Eng. B. 1991, 10, 149.<br/>[4] MOSUANG, T. E.; LOWTHER, J. E., J. Phys. Chem. Solids 2002, 63, 363-368.<br/>[5] CAZORLA, C.; GOULD, T., Sci. Adv. 2019, 5:eaau5832.<br/>[6] GUERINI, S.; MIWA, R. H.; SCHMIDT, T. M.; PIQUINI, P., Diam. Relat. Mater. 2008, 17, 1963.<br/>[7] BISWAS, A. <i>et al.</i>, J. Mater. Chem. C, 2024,12, 3053-3062.