CoxTi1－xO2－δ体材中氢退火引起的铁磁性及结构相变

利用固相反应法在700℃—1000℃不同的温度下、空气中烧结Co₃O₄ 和TiO₂混合物，制备了(Co₃O₄)_x/3(TiO2)_1-x(03，说明Co₃O₄与TiO₂反应形成了CoT iO₃；同时，在700 ℃低温和900 ℃以上的高温烧结样品中分别观察到了单相的 锐钛矿和金红石相结构.经高低温烧结的样品在500 ℃氢退火后，CoTiO₃相消失 ，锐钛矿相的Co_xTi_1-xO_2-δ形成.X射线光电子能谱(X PS)分析显示，氢退火样品中的Co以+2氧化价态存在，同时没有观察到金属态的Co，这说明 氢退火样品中的室温铁磁性不是源于金属Co颗粒的形成，而是与钙钛矿结构的CoTiO_{3< /sub>相的消失和锐钛矿型的CoxTi1-xO2-δ相的形成 有关.(Co3O4)x/3(TiO2)1-x( 0x}Ti_1-xO_2-δ相的本征铁磁性，伴随着结构相变而产生的Co离子之间的铁磁交换相互作用或 许是样品室温铁磁性产生的根本原因. 关键词： 室温铁磁性 结构相变 锐钛矿 氢退火

Room-temperature ferromagnetism in bulk CoxTi1－xO2－δ induced by the phase transformation in the hydrogenation sintering process

Paramagnetic (Co₃O₄)_x/3(TiO₂)_{1- x}(03O_{4 and TiO2 from 700 ℃ to 1000 ℃ in air. X-ray diffraction (XRD) re sults showed that perovskite CoTiO3 existed in all samples. Anatase p hase was also detected in samples sintered at 700 ℃ and when sintering the mixt ure at above 900 ℃, rutile phase formed with anatase phase disappearing. All sa mples exhibited room-temperature ferromagnetism (RTFM) after being hydrogenated in 10％ H2/Ar mixed atmosphere for 1 hour at 500 ℃. X-ray photoelect ron spectroscopy (XPS) showed that Co existed in the +2 formal oxidation state, and no Co clusters were detected. XRD showed that CoTiO3 disappeared and a new phase CoxTi1-xO2-δ formed after hyd rogenation. It is suggested that hydrogenation causes the phase transformation f rom CoTiO3 to CoxTi1-xO2-δ. RTFM of the sample originates from the intrinsic ferromagnetism of CoxTi1-xO2-δ. The exchange interaction between Co²⁺ occ urring with the phase transformation may be the essential reason for RTFM.}