Negative linear compressibility in a crystal of α-BiB3O6.

Negative linear compressibility (NLC), a rare and important mechanical effect with many application potentials, in a crystal of α-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. [ABSTRACT FROM AUTHOR]