(Georgia Institute of Technology, 1998)
Wang, Z. L. (Zhong Lin); Yin, Jinsong; Berta, Yolande; Zhang, Jiming
Magnetic oxides of (La,A)MnO₃ and (La,A)CoO₃ have two typical structural characteristics:
cations with mixed valences and oxygen vacancies, which are required to balance the charge
introduced by cation doping. The consequences introduced by each can be different, resulting in
different properties. It is important to quantitatively determine the percentage of charges balanced
by each, but this analysis is rather difficult particularly for thin films. This paper has demonstrated
that electron energy-loss spectroscopy (EELS) can be an effective technique for analyzing Mn and
Co magnetic oxides with the use of intensity ratio of white lines, leading to a new technique for
quantifying oxygen vacancies in functional and smart materials.
(Georgia Institute of Technology, 1997-09-29)
Yin, Jinsong; Wang, Z. L. (Zhong Lin)
Self-assembling of size, shape, and phase controlled nanocrystals into superlattices with translational and even orientational ordering is a new approach for engineering nanocrystal materials and devices. High purity tetrahedral nanocrystals of CoO, with edge lengths of 4.4±0.2 nm, were synthesized and separated from Co nanocrystals, using a novel magnetic field phase-selection technique. Self-assembling of the faceted CoO nanocrystals forms ordered superlattices, the structures of which are determined.
(Georgia Institute of Technology, 1997-06-23)
Wang, Z. L. (Zhong Lin); Yin, Jinsong; Jiang, Yongdong; Zhang, Jiming
Using the white line intensities, electron energy-loss spectroscopy in a transmission electron microscope has been employed to characterize the valence conversion and oxygen vacancies in La₁₋ₓCaₓMnO₃₋[subscript y]. For a nominal doping composition x = 0.33, the ratio of Mn³⁺ to Mn⁴ ⁺ is determined to be more than 0.25 but less than 0.5, and the content of oxygen vacancy y is no more than 0.065 (equivalent to 2.2 at. % of the oxygen content). At y[subscript max] = 0.065, 60% of the residual charge introduced by Ca doping is balanced by the conversion of Mn³⁺ to Mn⁴ ⁺and 40% by oxygen vacancy.