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Title: A high-temperature neutron diffraction study of Nb2AlC and TiNbAlC

In this paper, we report on the crystal structures of Nb2AlC and TiNbAlC actual composition (Ti0.45,Nb0.55)2AlC compounds determined from Rietveld analysis of neutron diffraction patterns in the 300-1173 K temperature range. The average linear thermal expansion coefficients of a Nb2AlC sample in the a and c directions are, respectively, 7.9(5)x10-6 K-1 and 7.7(5)x10-6 K-1 on one neutron diffractometer and 7.3(3)x10-6 K-1 and 7.0(2)x10-6 K-1 on a second diffractometer. The respective values for the (Ti0.45,Nb0.55)2AlC composition - only tested on one diffractometer - are 8.5(3)x10-6 K-1 and 7.5(5)x10-6 K-1. These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and 1 more along the basal planes than normal to them. In addition, when the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [1]
  1. Drexel Univ., Philadelphia, PA (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
1286845
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of the American Ceramic Society (Online)
Additional Journal Information:
Journal Name: Journal of the American Ceramic Society (Online); Journal Volume: 98; Journal Issue: 3; Journal ID: ISSN 1551-2916
Publisher:
American Ceramic Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE neutron diffraction; high temperature