Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 132, Issue 13, Pages 4822-4829Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja910745b
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Funding
- Ministerio de Ciencia e Innovacion [MAT2008-04587, PR2008-0164]
- Generalitat de Catalunya, Spain
- ERSRC
- Royal Society
- EaStCHEM
- Leverhulme Trust, U.K
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A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides 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 <= x <= 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.
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