High mechanical strength in Zn4B6O13 with an unique sodalite-cage structure

Abstract

Recently, a borate crystal Zn₄B₆O₁₃ (ZBO) has been focused on since it exhibits novel isotropic near-zero thermal expansion behavior in a wide temperature range. In this work, the mechanical properties in ZBO are studied by high-pressure X-ray diffraction and first-principles calculations. It is found that ZBO possesses the highest mechanical hardness in all known borates whose mechanical properties have been measured. The very high mechanical strength in ZBO mainly originates from the resistance of strong Zn–O bonds to the rotation among BO₄ tetrahedra in the unique sodalite-cage structure. Moreover, ZBO shows relatively high mechanical resistance to the axial and shear stress and exhibits high optical transparence in the ultraviolet spectral region under high pressure. Benefitting from these good properties, ZBO may find potential applications in high-precision optical facilities used at extreme conditions under complex environments.