The fracture toughness of zb-BAs evaluated within the Mazhnik-Oganov model , K Ic = 1.4 MPa•m ½ , agrees well with the experimental value of 1.2 MPa•m ½ , indicating that cubic boron arsenide (as well as qtz polymorph) is more brittle than cubic BN (2.8 MPa•m ½ ) and cubic BP (1.8 MPa•m ½ ). Hypothetical boron antimonide and boron bismuthate (both zinc-blende and qtz polymorphs) were found to be even more brittle (see Table ).