First principles investigations of the structural, elastic, electronic, vibrational and thermodynamic properties of hexagonal XAl2O4 (X = Cd, Ca and Sr)

Developing functional semiconductors for electronics, catalysis and photo electrochemical cells (PECs) that will take place of conventional semiconductors is very important. Despite intensive studies conducted about semiconductors, it is still a challenging issue to find more stable, functional, nontoxic and cheap materials for future electronic applications. Spinel oxides are among the promising materials that can be used as semiconductors due to their suitable band gap values. Here we study the structural, elastic, electronic, vibrational and thermodynamic properties of hexagonal XAl2O4 (X?=?Cd, Ca and Sr) spinels with space group P63 using first principles methods. The electronic band structure of XAl2O4 (X?=?Cd, Ca and Sr) reveales that the examined materials are direct band gap semiconductors. The calculated elastic constants and the phonon spectrum along high symmetry directions show that these materials are mechanically stable since they satisfy the generalised stability condition. Contrary, due to negative phonons at some high symmetry points XAl2O4 (X?=?Cd, Ca and Sr) spinels are dynamically unstable. Results obtained in this study show that of XAl2O4 (X?=?Cd, Ca and Sr) spinels are very promising for future electronic, catalysis and PECs applications.