Use Griffith's relation to solve:
(a) Calculate the surface energy of MgO crystal with (110) planes exposed. Assume an appropriate coordination number and take x = 1. The heat of sublimation of MgO is assumed to be 146 kcal/mol. (1 cal = 4.184 J). Assuming that the fracture occurs along the (110) planes, calculate the theoretical fracture strength (cohesive strength) of MgO, if the Young's modulus is 294.7 GPa. How does this value compare when a pre-existing crack of 500 nm is present in the (110) planes using Griffith's relation? Radius of Mg2+: 72 pm; O2-: 140 pm. Lattice parameter of MgO: 0.421 nm.