Structural, magnetic and electronic properties of EuTi0.5W0.5O3-xNx perovskite oxynitrides

EuTi0.5W0.5O3-xNx oxynitrides with nitrogen contents between 0.87 and 1.63 have been synthesized by ammonolysis of EuTi0.5W0.5O4 scheelite at high temperature. They are B-site disordered perovskites that show two different crystal symmetries as a function of the nitrogen content, changing at x near 1.3 from cubic Pm-3m to orthorhombic Pbnm. The nitriding degree is tuned by the ammonia flow rate and synthesis temperature, and determines the oxidation states of the cations and the equilibrium Eu2+ + W6+ <-> Eu3+ +W5+ promoting the decrease of the tolerance factor and the structural transition for large x values and electronic reconstructions. Accompanying the symmetry lowering, the nature of the magnetic order of Eu2+ moments changes from ferromagnetic to antiferromagnetic as a result of a complex interplay of antiferromagnetic/ferromagnetic superexchange interactions balanced by structural effects and the carrier-mediated magnetic exchange between Eu2+ ions.