Ordering energies and occupancies in doped TiAl, and dedicated ALCHEMI instrumentation

John Spence, N. Jiang, Uwe Weierstall

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Alloy design has been a lifelong interest of Gareth Thomas, and modern design algorithms include atomistic parameters which are obtainable from new electron microscope techniques such as ALCHEMI. In this paper, we discuss the relevance of ALCHEMI site occupancy measurements to intermetallic alloys, and summarize prior work. The results are found to lie in regions of a site-occupancy diagram (SOC) relating ordering energies to occupancy, as predicted by the Bragg-Williams theory of short-range order. These predictions also explain previous inconsistencies in the ALCHEMI measurements. A diffraction camera and X-ray detector system of novel design is proposed for dedicated ALCHEMI analysis for substitutional and interstitial dopant site-occupancy measurement, and details of the design given. Using this novel hardware design, the data-collection times for two-dimensional ALCHEMI patterns should be reduced by an order of magnitude or more, and the full data collection process automated. The resulting occupancy information can provide essential input parameters for atomistic alloy design algorithms, and can provide entirely new information on interstitial occupancies in minerals, ceramics, semiconductors, and alloys.

Original languageEnglish (US)
Pages (from-to)241-246
Number of pages6
JournalMicroscopy and Microanalysis
Issue number4
StatePublished - Aug 2002


  • Intermetallic alloys
  • Ordering
  • Site-occupancy

ASJC Scopus subject areas

  • Instrumentation


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