The hunt for LaFeSbO: Synthesis of La2SbO2 and a case of mistaken identity

The phase La2SbO2 has been identified and characterized in the course of our efforts to realize LaFeSbO, a composition of great interest to the superconductor community. The compound La2SbO2 is a tetragonal layered oxypnictide containing La2O2 layers similar to LaMPnO compositions (where M=transition metal, Pn=pnictide) separated by pnictide anion layers. In order to better understand why LaFeSbO has remained elusive, density functional theory calculations have been used to determine the ground state heats of formation for LaFeSbO, La2SbO2, and other competing phases within the La–Fe–Sb–O system, as well as the phonon spectrum for LaFeSbO. These efforts suggest that LaFeSbO is a potentially metastable composition.