Structure of Ce₂Pt₆Ga₁₅: interplanar disorder from the Ce₂Ga₃ layers

Abstract

The structure of the heavy fermion compound CezPt6Gal5 has been determined from neutron powder and X-ray/neutron single-crystal diffraction. Examination of symmetry equivalence among the single-crystal data, as well as the good fit of the powder data to the final structural arrangement, with all the atoms on symmetry sites, suggests that the correct space group is P63/mmc. The structure is unusual in that Ce layers have 1/3 of the Ce atoms replaced by groups of three Ga atoms; distances between atoms in these planes suggest this substitution must occur in a concerted fashion. The refined occupancies lead to a stoichiometry near Ce2Pt6Gals, consistent with such an arrangement. In addition, single-crystal neutron diffraction data show columns of weak diffuse scattering along the <001> axes, suggesting disorder arising from a lack of registration of successive Ce2Ga3 layers (lying half a cell length or 8.27 A apart along z) and a 3 x 3 × 1 supercell. This disorder is very likely responsible for the low resistance ratio of approximately unity measured for single crystal samples.

Magnetic Properties of theRE2Pt6X15(RE= Y, La–Nd, Sm, Gd–Lu;X= Al, Ga) Series

“…The lattice parameters of the RE 2 Pt 6 X 15 ( X = Al, Ga) series were refined from Guinier powder patterns using the hexagonal subcell of the RE 0.67 Pt 2 Al 5 series along with space group P 6 3 / mmc . The lattice parameters, including the ones from the literature, are listed in Table .…”

“…For Gd 0.67 Pt 2 Al 5 (≡ Gd 2 Pt 6 Al 15 ), antiferromagnetic ordering at a Néel temperature of T N = 7.5 K and 8 K was reported, single crystals of Yb 2 Pt 6 Al 15 were found to exhibit a broad maximum at low temperatures, in line with a Kondo lattice system with a large degeneracy of the local moments . For the heavier homologue Ga, also some compounds with the RE 0.67 Pt 2 Ga 5 / RE 2 Pt 6 Ga 15 composition ( RE = La, Ce, Pr, Nd, Sm, Gd, Er,) have been reported to crystallize in the Sc 0.6 Fe 2 Si 4.9 type structure. Of these, Ce 2 Pt 6 Ga 15 was characterized to be a heavy fermion material , .…”

“…Of these, Ce 2 Pt 6 Ga 15 was characterized to be a heavy fermion material , . Neutron diffraction experiments revealed a disordered structure, the modulated superstructure could not be solved and refined. Furthermore, the basic magnetic properties have been reported for Pr 2 Pt 6 Ga 15 ( T m = 16 K), Nd 2 Pt 6 Ga 15 ( T m = 10 K), Sm 2 Pt 6 Ga 15 ( T m = 8 K), Gd 2 Pt 6 Ga 15 ( T m = 9 K) and Er 2 Pt 6 Ga 15 (no T m reported) .…”

Non-Fermi liquid behavior on heavy-fermion system Ce2Pt6Ga15

“…The resultant crystals are in the form of hexagonal prisms, reflecting thier intrinsic crystal structure with typical dimensions of 4 × 4 × 10 mm. The crystallographic characterization is performed by means of the x-ray powder diffraction on crushed pieces of obtained single crystals [5]. No traces of impurity phases are detected.…”

“…It is reported that Ce 2 Pt 6 Ga 15 crystallizes in the hexagonal Ce 4 Pt 12 Ga 30 -type structure with the space group P6 3 /mmc [5]. This structure has an intrinsic two dimensional character with a large ratio c/a ∼ 4.…”