Review
Version 1
Preserved in Portico This version is not peer-reviewed
Phase Transitions in Boron Carbide
Version 1
: Received: 1 September 2023 / Approved: 4 September 2023 / Online: 5 September 2023 (03:29:18 CEST)
A peer-reviewed article of this Preprint also exists.
Werheit, H. Phase Transitions in Boron Carbide. Materials 2023, 16, 6734. Werheit, H. Phase Transitions in Boron Carbide. Materials 2023, 16, 6734.
Abstract
The idealized rhombohedral unit cell of boron carbide is formed by a 12-atom icosahedron and a 3-atom linear chain. Phase transitions are second order and caused by the exchange of B and C sites or by vacancies in the structure. Nevertheless, the impact of such minimal structural changes on the properties can be significant. As the X-ray scattering cross sections of B and C atoms are very similar, the capability of X-ray fine structure investigation is restricted. Phonon spectroscopy helps closing this gap. Phase transitions known to date have been identified due to significant changes of properties: (1) The phase transition near the chemical composition B8C by clear change of the electronic structure; (2) The endothermic temperature-dependent phase transition at 712 K by the according change of specific heat; (3) The high-pressure phase transition at 33.2 GPa by the drastic change of optical appearance from opacity to transparency. These phase transitions affect IR- and Raman-active phonons and other solid-state properties. The phase transitions at B~8C and 712 K mean that a well-defined distorted structure is converted into another one each. In the high-pressure phase transition, an apparently well-defined distorted structure changes into a highly ordered one. In all these cases, the distribution of polar C atoms in the icosahedra plays a crucial role.
Keywords
boron carbide; phase transition; structural disorder; electronic properties; phonons
Subject
Physical Sciences, Condensed Matter Physics
Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Comments (0)
We encourage comments and feedback from a broad range of readers. See criteria for comments and our Diversity statement.
Leave a public commentSend a private comment to the author(s)
* All users must log in before leaving a comment