a. Boron nitride, BN, has a graphite-like layered structure in which the layers have eclipsed alignment where the B and N atoms in alternative layers in the direction perpendicular to the layers. Rationalize the difference between this structure and the structure of graphite.
b. It has been found that a second form of BN can be obtained by subjecting BN to a pressure of 85,000 atm at 1800C. This form of BN is the second hardest substance known. Suggest a structure for the second form, and explain your reasoning.