Détermination structurale de Nd 2Ge 2O 7

The neodymium germanate Nd ₂Ge ₂O ₇ crystallizes in the triclinic P overline1 space group with a = 37.6093(99), b = 6.9222(3), c = 6.9234(12), Å, α = 91.456(13), β = 90.728(17), γ = 95.150(16)°, and Z = 12. The unit cell is built of 6 isolated GeO ₄ tetrahedra, 6 Ge ₃O ₁₀ groups, and 24 NdO ₇ or NdO ₈ polyhedra. The heavy atoms are distributed in plans parallel to (100) and regularly spaced. The structure can be viewed as the stacking of 6- and 12-Å-wide blocks parallel to (100) with the same composition. It can also be described as alternated Nd or Ge atomic slices parallel to ( 31 overline1). Comparisons of these features with the already known lanthanide germanate structures are made, particularly with Gd ₂Ge ₂O ₇. The crystals Nd ₂Ge ₂O ₇ are frequently twinned; a structural interpretation of twinning is proposed.