A NiAs/Ni2In-Type Phase Ni1+xSn (0.35<x<0.45) with Incommensurate Occupational Ordering of Ni

✍ Scribed by A. Leineweber; M. Ellner; E.J. Mittemeijer

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 493 KB
• Volume: 159
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9150

✦ Synopsis

The previously reported, ordered low-temperature NiAs/ Ni 2 In-type phase Ni 1؉x Sn comprises in the concentration range 0.35 < x < 0.53 in fact two separate, ordered phases. Both phases are based on a NiAs-type arrangement, 99NiSn,:: with the additional Ni atoms distributed over the trigonal+bipyramidal interstitial sites in an ordered way. Around the ideal composition Ni 3 Sn 2 (0.45 < x < 0.53), the earlier reported commensurate structure occurs, termed the 99LT phase,:: in which the longrange ordering leads to Pbnm symmetry with unit cell parameters a LT +2a HT , b LT +3 1/ 2 a HT , c LT +c HT , where the subscript HT refers to the corresponding, disordered hexagonal high-temperature phase. For lower Ni contents (0.35 < x < 0.45) an incommensurate phase, that is termed 99LT: phase,:: occurs with a crystal structure closely related to the LT phase. According to X-ray powder di4raction and selected area electron di4raction analyses, the average unit cell exhibits orthorhombic Cmcm symmetry, has unit cell parameters a orth +a HT , b orth +3 1/ 2 b HT , c orth +c HT , and a modulation vector ql ‫؍‬ al * orth with +0.493 for x ‫؍‬ 0.44 and +0.428 for x ‫؍‬ 0.35. The LT phase may be regarded as a 99lock-in:: phase of the LT: phase with ‫؍‬ 1 2 . A model for the long-range occupational ordering of Ni on the trigonal+bipyramidal interstitial sites has been suggested.