Crystal structure of Al_2.95Cr_0.59, a phase closely related to the η-phase in the binary Al-Cr system

The monoclinic η-phase in the binary Al-Cr system was initially named by Bradley & Lu [Bradley & Lu (1937 ▸). J. Inst. Met. 60, 319-337] as having the composition Al₁₁Cr₂ (Al:Cr ratio = 5.5:1). Its crystal structure was later refined [Cao & Kuo (2008). J. Alloys Compd. 458, 30, 319-337] to have a slightly lower Al content (Al:Cr ratio = 5.16:1). In the present work, a monoclinic phase with composition Al_2.95Cr_0.59 (Al:Cr ratio = 5.04:1) was obtained by high-pressure sinter-ing (HPS) of a stoichiometric Al₁₁Cr₂ mixture. Structure analysis of this phase, hereafter named η', revealed a close relationship to the previously reported η-Al₁₁Cr₂ structure, but with different mixed-occupied sites. Five fully occupied sites exhibit refined site occupation factors of 0.899 (5), 0.984 (4), 0.977 (5), 0.946 (4) and 0.945 (4) for the corresponding Al atoms. Moreover, there are no split Al sites in the η'-structure as reported for the η-structure. The refined chemical composition of the η'-phase revealed that it comprises two Al atoms fewer and two Cr atoms more than the previously reported η-Al₁₁Cr₂ phase.