Negative linear compressibility in a crystal of alpha-BiB3O6

Negative linear compressibility (NLC), a rare and important mechanical effect with many application potentials, in a crystal of alpha-BiB3O6 (BIBO) is comprehensively investigated using first-principles calculations and high-pressure synchrotron X-ray diffraction experiments. The results indicate that the BIBO crystal exhibits the second largest NLC among all known inorganic materials over a broad pressure range. This unusual NLC behaviour is due to the rotation and displacement of the rigid [BO3] and [BO4] building units that result in hinge motion in an umbrella-like topology. More importantly, the parallel-polar lone-pair electrons on the Bi3+ cations act as "umbrella stands" to withstand the B-O hinges, thus significantly enhancing the NLC effect. BIBO presents a unique example of a "collapsible umbrella" mechanism for achieving NLC, which could be applied to other framework materials with lone-pair electrons.National Scientific Foundations of China [11474292]; China "863" project [2015AA034203]; "973" Project [2014CB921301]; Special Foundation of the Director of Technical Institute of Physics and Chemistry (TIPC); Opening Project of the Key Laboratory of Cryogenics in TIPC; Chinese Academy of SciencesSCI(E)PubMedARTICLEwl276@hust.edu.cn; zslin@mail.ipc.ac.cn13432