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A High‐Temperature Neutron Diffraction Study of Nb 2 AlC and TiNbAlC
Author(s) -
Bentzel Grady W.,
Lane Nina J.,
Vogel Sven C.,
An Ke,
Barsoum Michel W.,
Caspi El'ad N.
Publication year - 2015
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.13366
Subject(s) - diffractometer , neutron diffraction , materials science , crystallography , rietveld refinement , diffraction , analytical chemistry (journal) , powder diffractometer , crystal structure , chemistry , physics , optics , chromatography
Herein, we report on the crystal structures of Nb 2 AlC and TiNbAlC—actual composition (Ti 0.45 ,Nb 0.55 ) 2 AlC—compounds determined from Rietveld analysis of neutron diffraction patterns in the 300–1173 K temperature range. The average linear thermal expansion coefficients of a Nb 2 AlC sample in the a and c directions are, respectively, 7.9(5) × 10 −6 and 7.7(5) × 10 −6 K −1 on one neutron diffractometer and 7.3(3) × 10 −6 and 7.0(2) × 10 −6 K −1 on a second diffractometer. The respective values for the (Ti 0.45 ,Nb 0.55 ) 2 AlC composition—only tested on one diffractometer—are 8.5(3) × 10 −6 and 7.5(5) × 10 −6 K −1 . These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs 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.