Magnetic And Transport Properties Of Polycrystalline La1-Xbaxmno3 (X=0, 0.11, And 0.33) Annealed In Different Conditions

The hole-doped rare-earth manganite La1-xBaxMnO3 has become the subject of intense interest recently. We compared the magnetic and transport properties of polycrystalline La1-xBaxMnO3 annealed in different conditions. Polycrystalline La1-xBaxMnO3 (x=0, 0.11, 0.33) was annealed in the presence of O-2, N-2, and N-2 with graphite powder nearby (as oxygen getter), or 95% Ar+5% H-2 gas mixture (AH) at 700 degrees C for 3 h. LaMnO3+delta (x=0) was turned into LaMnO3+xi (xi > delta) or LaMnO3 when annealing occurred in the presence of O-2 or reducing agent, respectively. Interestingly, a mixture of oxygen excessive phase La0.89Ba0.11MnO3+delta and oxygen stoichiometric phase La0.89Ba0.11MnO3 (x=0.11) was produced when annealing happened in the presence of O-2, with La0.89Ba0.11MnO3+delta on the surface of the mixture. Similar changes were found when using other gas conditions. For x=0.33, only La0.67Ba0.33MnO3 was produced, in which the number of oxygen atoms could be further reduced by annealing in the presence of AH. We concluded that the undoped and low doped rare-earth manganites La1-xBaxMnO3 easily take more than three oxygen atoms, and the excessive oxygen can be removed by annealing in reducing condition. (C) 2010 Elsevier B.V. All rights reserved.