Low albite, NaAlSi₃O₈: Neutron diffraction study of crystal structure at 13 K Available to Purchase

The crystal structure of low albite, Amelia, Virginia, was determined at 13 K by neutron diffraction (a = 8.1151(8), b = 12.7621(25), c = 7.1576(6) Å, α = 94.218(12)°, β = 116.803(8)°, γ = 87.707(13)°; C1). Mean T-O distances are T₁O 1.743, T₁m 1.611, T₂O 1.615, T₂m 1.616 Å. Refinement of scattering lengths yields the following populations: T₁O 0.997(4) Al; T₁m 1.001(3) Si; T₂O 1.002(3) Si; T₂m 1.006(4) Si; Na 0.972(1) Na. The displacement of the Na atom is represented by an ellipsoid (root-mean-square amplitudes 0.065, 0.073, and 0.108 Å) whose shorter axes are constrained by the five near oxygen atoms at 2.361, 2.419, 2.438, 2.500, and 2.614 Å. The displacements of all atoms (B_iso: Si 0.19, Al 0.20, O 0.29-0.42, Na 0.56 Ų) are similar to those for natrolite and scolecite at 20 K and are consistent with qualitative expectations for the zero-point energy. Stereochemical interpretation of the T-O distances at low temperature in low albite, natrolite, scolecite, quartz, and cristobalite is incomplete when only first neighbors are considered.