First-principle study on O–A–O dumbbell of delafossite crystal

• From Cu to Ag, the increase of c parameters is attributed to electrostatic repulsion.
• The difference charge density shows the bonding of Ag–O is more covalent.
• Effective mass of AgAlO2 along the [0 0 1] direction is smaller than that of CuAlO2.

Taking CuAlO2 and AgAlO2 for instance, O–A–O dumbbell-related electronic properties in delafossite lattice were systematically investigated by using the first-principles projector augmented wave method. Compared with CuAlO2, the increase of c parameter comes from the volume effect and electrostatic repulsion due to excess overlap of electron clouds between Ag and O atoms. The difference charge density demonstrates the interaction of A dz2 and O pz orbitals, and suggests the stronger covalent hybridization of Ag–O. The effective masses of these two compounds along [0 0 1] direction are remarkably different. Ag vacancy has lower formation energy relative to Cu one, which could benefit from longer c axis. The differences derived from O–A–O dumbbell could be helpful for thoroughly understanding its role in delafossite lattice.