The Nanoscale Ordered MAterials Diffractometer NOMAD at the Spallation Neutron Source SNS

Neuefeind, J.; Feygenson, Mikhail; Carruth, John William; Hoffmann, Ron; Chipley, K.K.

doi:10.1016/j.nimb.2012.05.037

Cited by 347 publications

(285 citation statements)

References 20 publications

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“…Neutron total scattering experiments were performed on an N-deuterated sample using the NOMAD instrument (BL-1B) 88 at the Spallation Neutron Source at Oak Ridge National Laboratory. The as-prepared dried powders were transferred into a mortar and pestle and thoroughly ground to a fine powder.…”

Section: Resultsmentioning

confidence: 99%

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

et al. 2017

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The role of organic molecular cations in the high-performance perovskite photovoltaic absorbers, methylammonium lead iodide (MAPbI 3 ) and formamidinium lead iodide (FAPbI 3 ), has been an enigmatic subject of great interest. Beyond aiding in the ease of processing of thin films for photovoltaic devices, there have been suggestions that many of the remarkable properties of the halide perovskites can be attributed to the dipolar nature and the dynamic behavior of these cations. Here, we establish the dynamics of the molecular cations in FAPbI 3 between 4 K and 340 K and the nature of their interaction with the surrounding inorganic cage using a combination of solid state nuclear magnetic resonance and dielectric spectroscopies, neutron scattering, calorimetry, and ab initio calculations. Detailed comparisons of the reported temperature dependence of the dynamics of MAPbI 3 are then carried out which reveal the molecular ions in the two different compounds to exhibit very similar rotation rates (≈8 ps) at room temperature, despite differences in other temperature regimes.For FA, rotation about the N···N axis, which reorients the molecular dipole, is the dominant motion in all phases, with an activation barrier of ≈21 meV in the ambient phase, compared to ≈110 meV for the analogous dipole reorientation of MA. Geometrical frustration of the molecule-cage interaction in FAPbI 3 produces a disordered γ-phase and subsequent glassy freezing at yet lower temperatures. Hydrogen bonds suggested by atom-atom distances from neutron total scattering experiments imply a substantial role for the molecules in directing structure and dictating properties. The temperature dependence of reorientation of the dipolar molecular cations systematically described here can clarify various hypotheses including large-polaron charge transport and fugitive electron spin polarization that have been invoked in the context of these unusual materials.2

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Section: Resultsmentioning

confidence: 99%

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

et al. 2017

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“…2. The fitting of the diffraction pattern with the model calculated using The NOMAD is a medium-range resolution instrument ( ∆d d ∼0.8%) [19] and within this resolution, no Bragg peak broadening is observed unlike the case of high pressure annealed LaO 1−x F x BiS 2 in which (00l) peaks were severely compromised. [20,21] The diffraction pattern can be fit well with the P4/nmm symmetry for both superconducting and nonsuperconducting compositions.…”

Section: Resultsmentioning

confidence: 99%

Charge Fluctuations in the NdO₁₋_xF_xBiS₂ Superconductors

et al. 2017

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The local atomic structure of superconducting NdO 1−x F x BiS 2 (x =0.2 and 0.4) is investigated using neutron diffraction and the pair density function analysis technique. In the nonsuperconducting x=0.2 composition, ferrodistortive displacements of the pyramidal sulfur ions break the tetragonal symmetry and a superlattice structure emerges with peaks appearing at h + k odd reflections superimposed on the even reflections of the P 4/nmm symmetry. In the superconducting x=0.4 composition, similar ferrodistortive displacements are observed but with different magnitudes coupled with in-plane Bi distortions. The distortions are indicative of charge fluctuations that may lead to charge localization and suppression of superconductivity.

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“…Neutron diffraction experiments were performed at the ORNL Spallation Neutron Source (SNS) 65 using instruments optimized for studies of local structures (NOMAD, Nanoscale-ordered Materials Diffractometer) 40 and long-range crystal ordering (POWGEN) 66 . The use of both NOMAD and POWGEN was motivated by the expectation that the present HEAs have distinct local features (for example, lattice distortions and local ordering), as well as long-range crystal order.…”

Section: Methodsmentioning

confidence: 99%

“…To understand the local-ordering behaviour, pair distribution function (PDF) analyses of the neutron diffraction data were carried out [40][41][42] . At room temperature (Fig.…”

Section: Room Temperature Microstructuresmentioning

confidence: 99%

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

et al. 2015

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The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as 'high-entropy alloys'. Understanding the elemental distribution, and, thus, the evolution of the configurational entropy during solidification, is undertaken in the present study using the Al 1.3 CoCrCuFeNi model alloy. Here we show that, even when the material undergoes elemental segregation, precipitation, chemical ordering and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. The results suggest that the high-entropy alloy-design strategy may be applied to a wide range of complex materials, and should not be limited to the goal of creating single-phase solid solutions.

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The Nanoscale Ordered MAterials Diffractometer NOMAD at the Spallation Neutron Source SNS

Cited by 347 publications

References 20 publications

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

Charge Fluctuations in the NdO₁₋_xF_xBiS₂ Superconductors

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

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The Nanoscale Ordered MAterials Diffractometer NOMAD at the Spallation Neutron Source SNS

Cited by 347 publications

References 20 publications

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

Universal Dynamics of Molecular Reorientation in Hybrid Lead Iodide Perovskites

Charge Fluctuations in the NdO1−xFxBiS2 Superconductors

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

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Charge Fluctuations in the NdO₁₋_xF_xBiS₂ Superconductors