Incommensurately modulated LT''-Ni{sub 1+{delta}}Sn (delta=0.60, 0.63): Rietveld refinement, line-broadening analysis and structural relation with LT- and LT'-Ni{sub 1+{delta}}Sn

Journal Article · Wed Jul 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.04.019· OSTI ID:21370492

Leineweber, A ^[1]

---

1. Max Planck Institute for Metals Research, Heisenbergstrasse 3, 70569 Stuttgart (Germany)

X-ray powder diffraction data of NiAs/Ni{sub 2}In-type Ni{sub 1.60}Sn and Ni{sub 1.63}Sn alloys annealed at or below about 573 K reveal the development of an incommensurately ordered phase called LT''. In this phase Ni(2) atoms occupy partially the trigonal-bipyramidal interstices formed by five Sn within an NiAs-type arrangement Ni(1)Sn. The modulated occupational ordering of Ni(2) in the LT'' phase can be described in the superspace group Cmcm(alpha00)0 s 0, and the parameters describing this occupational modulation were refined together with atomic displacement modulations using the Rietveld method. The structure parameters revealed close structural analogies of the LT'' phase with the previously reported commensurate LT-Ni{sub 1+{delta}}Sn and incommensurate LT'-Ni{sub 1+{delta}}Sn phases (A. Leineweber, J. Solid State Chem. 177 (2004) 1197-1212), which both occur for lower Ni contents than the LT'' phase. The 1st-order satellite reflections visible in the powder-diffraction patterns exhibit, with respect to the fundamental reflections, a considerable diffraction-line broadening, caused by a small size of the particularly ordered domains. This small-domain-size broadening was successfully described by a recently developed reflection-index (hklm) dependent (anisotropic) line-broadening model (A. Leineweber, V. Petricek, J. Appl. Crystallogr. 40 (2007) 1027-1034) designed to consider the effect of fluctuations of the lattice metrics on the peak widths in powder diffraction patterns of incommensurately modulated crystal structures. The small domain sizes encountered for the LT'' phase indicate that domain coarsening is much more difficult than for the LT and LT' phases. This special feature of the LT'' phase goes along with a compared to the LT and LT' phases absent orthorhombic distortion and the low ordering temperature, which are discussed as a consequence of the ordering patterns due to the Ni(2) atoms. - Graphical abstract: Approximant structure of incommensurately modulated LT''-Ni{sub 1.60}Sn, forming below 573 K from the disordered phase. The phase has a close structural relationship to the LT and LT' phases occurring at lower Ni contents.

• OSTI ID: 21370492
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 7; Other Information: DOI: 10.1016/j.jssc.2009.04.019; PII: S0022-4596(09)00180-7; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANISOTROPY
ANNEALING
ARSENIC ALLOYS
ATOMIC DISPLACEMENTS
LINE BROADENING
NICKEL ALLOYS
ORDER-DISORDER TRANSFORMATIONS
ORTHORHOMBIC LATTICES
TEMPERATURE RANGE 0400-1000 K
TIN ALLOYS
X-RAY DIFFRACTION
ALLOYS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
HEAT TREATMENTS
PHASE TRANSFORMATIONS
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
SCATTERING
TEMPERATURE RANGE
TRANSITION ELEMENT ALLOYS