Acta Crystallographica Section B

Structural Science

Volume 62, Part 2 (April 2006)

research papers

Acta Cryst. (2006). B62, 173-189 [ doi:10.1107/S0108768106003314 ]

Structure of Ce₂RhIn₈: an example of complementary use of high-resolution neutron powder diffraction and reciprocal-space mapping to study complex materials

E. G. Moshopoulou, R. M. Ibberson, J. L. Sarrao, J. D. Thompson and Z. Fisk

Abstract: The room-temperature crystal structure of the heavy fermion antiferromagnet Ce₂RhIn₈, dicerium rhodium octaindide, has been studied by a combination of high-resolution synchrotron X-ray reciprocal-space mapping of single crystals and high-resolution time-of-flight neutron powder diffraction. The structure is disordered, exhibiting a complex interplay of non-periodic, partially correlated planar defects, coexistence and segregation of polytypic phases (induced by periodic planar `defects'), mosaicity (i.e. domain misalignment) and non-uniform strain. These effects evolve as a function of temperature in a complicated way, but they remain down to low temperatures. The room-temperature diffraction data are best represented by a complex mixture of two polytypic phases, which are affected by non-periodic, partially correlated planar defects, differ slightly in their tetragonal structures, and exhibit different mosaicities and strain values. Therefore, Ce₂RhIn₈ approaches the paracrystalline state, rather than the classic crystalline state and thus several of the concepts of conventional single-crystal crystallography are inapplicable. The structural results are discussed in the context of the role of disorder in the heavy-fermion state and in the interplay between superconductivity and magnetism.

Keywords: neutron powder diffraction; reciprocal-space mapping; polytypic phases; mosaicity; fermion antiferromagnet.


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