scholarly journals The incommensurately modulated structures of low-temperature labradorite feldspars: a single-crystal X-ray and neutron diffraction study

2020 ◽  
Vol 76 (1) ◽  
pp. 93-107
Author(s):  
Shiyun Jin ◽  
Huifang Xu ◽  
Xiaoping Wang ◽  
Ryan Jacobs ◽  
Dane Morgan
Keyword(s):  
Low Temperature ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Neutron Diffraction Study ◽  
Neutron Diffraction Data ◽  
X Ray Diffraction ◽  
Subsolidus Phase ◽  
X Ray ◽  
Modulated Structures

Labradorite feldspars of the plagioclase solid solution series have been known for their complicated subsolidus phase relations and enigmatic incommensurately modulated structures. Characterized by the irrationally indexed e-reflections in the diffraction pattern, e-labradorite shows the largest variation in the incommensurate ordering states among the e-plagioclase structures. The strongly ordered low-temperature e-labradorite is one of the last missing pieces of the e-plagioclase puzzle. Nine plutonic and metamorphic labradorite feldspar samples from Canada, Ukraine, Minnesota (USA), Tanzania and Greenland with compositions ranging from An52.5 to An68 were studied with single-crystal X-ray diffraction. Two crystals from Labrador, Canada, and Duluth, MN, USA, with wide enough twin lamellae were analyzed with single-crystal neutron diffraction. The incommensurately modulated structures of e-plagioclase are refined for the first time with neutron diffraction data, which confirmed that the T—O distance modulation in the low-temperature e-plagioclase results from the Al–Si ordering in the framework. Detailed configurations of the M site are also observed in the structures refined from neutron diffraction data, which were not possible to see with X-ray diffraction data. The relation between the q-vectors and the mole% An composition is revealed for the entire compositional range of e-plagioclase, from An25 to An75. The previously proposed two-trend relation depending on the cooling rate and phase transition path is confirmed. A new classification of e-plagioclase (e α, e β and e γ) is proposed based on the q-vector of the structure, which makes it an independent character from the presence/absence of density modulation. New parameters are proposed to quantify the ordering states of these complicated aperiodic structures of e-plagioclases, such as the difference between 〈T1o—O〉 and 〈T1m—O〉 at phase t = 0.2 or the normalized intensity of the (071\bar 1) reflection.

scholarly journals Accurate H-atom parameters for the two polymorphs of L-histidine at 5, 105 and 295 K

2021 ◽  
Vol 77 (5) ◽  
pp. 785-800
Author(s):  
Giulia Novelli ◽  
Charles J. McMonagle ◽  
Florian Kleemiss ◽  
Michael Probert ◽  
Horst Puschmann ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Crystal Packing ◽  
Basis Sets ◽  
X Ray Diffraction ◽  
X Ray ◽  
Refinement Method ◽  
Primary Amino ◽  
Precision And Accuracy

The crystal structure of the monoclinic polymorph of the primary amino acid L-histidine has been determined for the first time by single-crystal neutron diffraction, while that of the orthorhombic polymorph has been reinvestigated with an untwinned crystal, improving the experimental precision and accuracy. For each polymorph, neutron diffraction data were collected at 5, 105 and 295 K. Single-crystal X-ray diffraction experiments were also performed at the same temperatures. The two polymorphs, whose crystal packing is interpreted by intermolecular interaction energies calculated using the Pixel method, show differences in the energy and geometry of the hydrogen bond formed along the c direction. Taking advantage of the X-ray diffraction data collected at 5 K, the precision and accuracy of the new Hirshfeld atom refinement method implemented in NoSpherA2 were probed choosing various settings of the functionals and basis sets, together with the use of explicit clusters of molecules and enhanced rigid-body restraints for H atoms. Equivalent atomic coordinates and anisotropic displacement parameters were compared and found to agree well with those obtained from the corresponding neutron structural models.

scholarly journals Glycyl-L-alanine: a multi-temperature neutron study

2014 ◽  
Vol 70 (10) ◽  
pp. 949-952 ◽  
Author(s):  
Silvia C. Capelli ◽  
Hans-Beat Bürgi ◽  
Sax A. Mason ◽  
Dylan Jayatilaka
Keyword(s):  
Hydrogen Bonding ◽  
Neutron Diffraction ◽  
Diffraction Data ◽  
Neutron Diffraction Data ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hydrogen Bonding Interactions ◽  
Anisotropic Displacement Parameters

Neutron diffraction data have been collected at 12, 50, 150 and 295 K for the dipeptide glycyl-L-alanine, C5H10N2O3, in order to obtain accurate positional and anisotropic displacement parameters for the H atoms. The values of these parameters serve as a benchmark for assessing the equivalent parameters obtained from a so-called Hirshfeld-atom refinement of X-ray diffraction data described elsewhere [Capelliet al.(2014).IUCrJ,1, 361–379]. The flexibility of the glycyl-L-alanine molecule in the solid and the hydrogen-bonding interactions as a function of temperature are also considered.

A Re-investigation of the Crystal Structure of the Perovskite PbZrO3 by X-ray and Neutron Diffraction

1997 ◽  
Vol 53 (1) ◽  
pp. 135-142 ◽  
Author(s):  
D. L. Corker ◽  
A. M. Glazer ◽  
J. Dec ◽  
K. Roleder ◽  
R. W. Whatmore
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Lead Zirconate ◽  
Conclusive Evidence ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Investigations

The crystal structure of the perovskite lead zirconate PbZrO3 has been redetermined using single-crystal X-ray diffraction (Mo Kα radiation, λ = 0.71069 Å). Single-crystal data at 100 K: space group. Pbam, a = 5.884 (1), b = 11.787 (3), c = 8.231 (2) Å, V = 570.85 Å3 with Z = 8, μ = 612.6 cm−1, D x = 8.06 Mg m−3, F(000) = 1168, final R = 0.033, wR = 0.061 over 555 reflections with I > 2σ(I). An investigation is made into previous contradicting reports of a possible disorder in the O atoms and their origin by examining the crystal pseudo-symmetry. Information distinguishing an ordered and disordered oxygen substructure is shown to reside in weak l odd reflections. Because of their extremely low intensities these reflections have not contributed sufficiently in previous X-ray structure investigations and hence, to date, conclusive evidence differentiating between ordered and disordered models has not been possible. By collecting single-crystal X-ray data at low temperature and by using exceptionally long scans on selected hkl, l odd, reflections, a new accurate structure determination is presented and discussed, showing the true ordered oxygen positions. Because of the large difference in scattering factors between lead and oxygen when using X-rays, a neutron diffraction Rietveld refinement using polycrystalline samples (D1A instrument, ILL, λ = 1.90788 Å) is also reported as further evidence to support the true ordered oxygen structure revealed by the low-temperature X-ray analysis.

Structure of Ce2Pt6Ga15: interplanar disorder from the Ce2Ga3 layers

1996 ◽  
Vol 52 (4) ◽  
pp. 580-585 ◽  
Author(s):  
G. H. Kwei ◽  
A. C. Lawson ◽  
A. C. Larson ◽  
B. Morosin ◽  
E. M. Larson ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Diffuse Scattering ◽  
Heavy Fermion ◽  
Neutron Diffraction Data ◽  
Crystal Data ◽  
Single Crystal Diffraction ◽  
X Ray ◽  
A Cell

The structure of the heavy fermion compound Ce2Pt6Ga15 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 Ce2Pt6Ga15, 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 Å apart along z) and a 3 × 3 × 1 supercell. This disorder is very likely responsible for the low resistance ratio of approximately unity measured for single-crystal samples.

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