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Synchrotron X-ray and neutron investigation of the structure and thermal expansion of the monoclinic Al13Cr2 phase

DOI: 10.1016/j.jallcom.2018.12.132 DOI Help

Authors: E. Liotti (University of Oxford) , C. A. Kirk (University of Edinburgh; The Natural History Museum) , I. Todd (Sheffield University) , K. S. Knight (The Natural History Museum; University College London) , S. C. Hogg (Loughborough University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Alloys And Compounds

State: Published (Approved)
Published: December 2018
Diamond Proposal Number(s): 773

Abstract: The crystal structure of the Al13Cr2 intermetallic phase at 298 K was studied by synchrotron X-ray and neutron diffraction through the analysis of data collected on bulk samples, one in the as-cast condition, one after annealing at 773 K for 24 h and one for 168 h. Furthermore the thermal expansion behaviour of the structure was investigated for the first time in-situ up to 773 K. The diffraction patterns were analysed using whole pattern fitting techniques using the Le Bail and Pawley methods as well as the Rietveld method. The structure was found to be monoclinic with space group C2/m and lattice parameters a = 25.3101 Å, b = 7.6081 Å, c = 10.9689 Å and β = 128.704∘ at 298 K in the as-cast condition. From the temperature variation of the unit cell parameters the principal axes of the thermal expansion tensor were calculated. The largest principal axis has a magnitude of 1.66×10−5 K−1 and lies parallel to b, the second largest lies in the a-c plane at an angle of ∼ 37° from c in the direction of -a with a value 1.64×10−5 K−1 whereas the smallest lies at ∼ 53° to c in the direction of +a and has a value of 1.31×10−5 K−1. Analysis of the behaviour of the icosahedra revealed that their expansion is highly anisotropic and the level of anisotropy is related to the point symmetry of the central Cr atoms.

Journal Keywords: Al intermetallics; Structure thermal expansion; Synchrotron X-ray and neutron diffraction

Subject Areas: Materials

Instruments: I11-High Resolution Powder Diffraction