melting point of aluminium oxide and magnesium oxide

gaobo9109

1. The problem statement, all variables and given/known data
Why does magnesium oxide have higher melting point than aluminium oxide. If I follow the reasoning of lattice energy, aluminium oxide should have higher melting since its lattice energy is more exothermic. But in actual fact, m.p of magnesium oxide is 2830, much higher than that of aluminium oxide


2. Relevant equations



3. The attempt at a solution