The introduction of anion vacancies into complex metal oxides is a powerful method of controlling structure and properties by tailoring metal coordination environment and oxidation state. The hydride anion can effect reductive transformations of oxides inaccessible to conventional metal getters or gaseous reducing agents.[1] The A 2 B 2 O 7 pyrochlore structure [2] is important for properties as diverse as anion and mixed conduction, [3] superconductivity, [4] and colossal magnetoresistance, [5] but, in contrast to ABO 3 perovskite, there is little chemistry established for the low-temperature introduction of anion vacancies and generation of associated defect structures. Pyrochlore is well known for stabilizing high oxidation states on the octahedral B site; A ). Here we report the systematic low-temperature synthesis of pyrochlore systems with up to 90 % titanium(iii) on the octahedral sites.

The introduction of anion vacancies into complex metal oxides is a powerful method of controlling structure and properties by tailoring metal coordination environment and oxidation state. The hydride anion can effect reductive transformations of oxides inaccessible to conventional metal getters or gaseous reducing agents.[1] The A 2 B 2 O 7 pyrochlore structure [2] is important for properties as diverse as anion and mixed conduction, [3] superconductivity, [4] and colossal magnetoresistance, [5] but, in contrast to ABO 3 perovskite, there is little chemistry established for the low-temperature introduction of anion vacancies and generation of associated defect structures. Pyrochlore is well known for stabilizing high oxidation states on the octahedral B site; A ). Here we report the systematic low-temperature synthesis of pyrochlore systems with up to 90 % titanium(iii) on the octahedral sites.

Titanium Titanium I 4300 New Oxidation States and Defect Chemistry in the Pyrochlore Structure. -Pyrochlore systems with up to 90% Ti(III) on the octahedral sites are synthesized by reaction of Ln2Ti2O7 (Ln: Sm, Eu, Lu, Yb) and CaH2 below 700°C. The samples are characterized by powder XRD and neutron powder diffraction. Magnetization measurements indicate that the localized spins at the Ti centers are strongly coupled antiferromagnetically. -(BLUNDRED, G. D.; BRIDGES, C. A.; ROSSEINSKY*, M. J.; Angew.