Nanocrystalline ceramics show attractive properties in terms of superior hardness and strength. However, the lack of active energy absorbing mechanisms at low temperature causes those superstrong nanoceramics to show low fracture toughness. Cracks are observed to propagate through the grain boundaries (GBs), that in these systems account for a large fraction of the atomic volume. GBs intrinsically present unsatisfied chemical bonds, resulting in weak resistance for crack propagation. In truth, GB energy finds an inverse relation with interfacial bonding strength, such that a lower energy GB shall reflect stronger local bonds. In this work, we exploit the theory of GB energy reduction by solute excess to lower the excess energies in nanocrystalline zirconia. We demonstrate that the addition of La lowers the energies due to segregation, while minimizing the energy dispersion when comparing the different existing GBs. This causes cracks to be more effectively deflectedm significantly increasing toughness.