Minghui Yang, Judith Oró-Solé, Anna Kusmartseva, Amparo Fuertes*, and J. Paul Attfield,    
J. AM. CHEM. SOC. 9 VOL. 132, NO. 13, 2010

Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King’s Buildings, Mayfield Road, Edinburgh, EH9 3JZ, United Kingdom, and Institut de Ciència de Materials de Barcelona (CSIC), Campus U.A.B., 08193 Bellaterra, Spain

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y ) 0.04) and then EuWO1+xN2-x perovskites that show a wide range of compositions -0.16 e x e 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x < 0 regime corresponds to oxidation of Eu (hole doping of the Eu:4f band), whereas x > 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x)-0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified.