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Dopants Adsorbed as Single Atoms Prevent Degradation of Catalysts

Shibata N1, Pennycook SJ1, Gosnell TR2, Painter GS3, Shelton WA4, Becher PF3

Nature 428 (6984): 730-733 APR 15 2004

Full Article (PDF 420 KB)

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, key to the design of high-performance Si3N4 ceramics, has been sought for many years. Here, we show direct images of dopant atoms (La) within the nano-meter scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La to the crystalline surfaces which is essential for forming elongated grains and a toughened microstructure. While there has been a basis for the micro-scale design of ceramics to improve mechanical properties, this work addresses the atomic-level structural engineering required for the next generation of ceramics.

 
 
 
  1. Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,
  2. USAPixon LLC, 100 North Country Road, Setauket, New York 11733,
  3. USAMetals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,
  4. USA Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

 Oak Ridge National Laboratory