Neutron TOF Powder Diffraction

6.3 Neutron time-of-flight (TOF) powder diffraction Andreas Houben1, Yannick Meinerzhagen1 1RWTH Aachen University, Institute of Inorganic Chemistry Neutron time-of-flight (TOF) powder diffraction [1] is a powerful technique for solving crystal structures and investigating structural properties on the atomic/molecular level. It is applied on modern materials across various scientific fields, utilizing the neutrons unique capabilities in numerous aspects. TOF powder diffraction typically utilizes a pulsed neutron beam with a wide angular coverage detector system to simultaneously probe the lattice space distances d via tof/λ and 2θ according to Bragg’s law. Hence, when neutrons interact with a powdered sample, they are detected at different scattering angles depending on the material's crystal structure. By measuring the time from the pulse generation till reaching the detector for each neutron scattered at the sample, one can also reassign the wavelength. In general, powder diffraction is used within many different scientific communities and also materials, such like cements, lithium-ion batteries, fuel cell materials, hydrogen storage materials, magnetic materials, all kinds of oxides, or more advanced, possibly airor moisture sensitive chemical compounds, etc.. The particular strength of (TOF) neutron powder diffraction manifests, when unique information that is not available by complementary methods become accessible to characterize the materials structure or the structural behavior with changing temperature, pressure, electric or magnetic field, etc. and eventual phasetransitions occur. Finally, in situ or operando studies, e.g., of ongoing chemical reactions need to be mentioned. [2] Typical examples are samples with light elements like for example hydrogen or lithium next to heavy atoms, e.g., in batteries or more generally in energy or hydrogen storage materials. Similarly, also neighboring elements or even isotopes, e.g., hydrogen and deuterium can be nicely distinguished within neutron diffraction. Another domain of neutron scattering in general and also neutron TOF powder diffraction is the analysis of magnetic systems, because of the neutron’s magnetic dipole moment. Examples are samples that show cooperative magnetism, such as ferro-, antiferroor ferrimagnetism, or even more complicated quantum phenomes. In the following we present a set of metadata tailored to neutron TOF powder diffraction experiments. As an example, we apply the proposed schema to a hypothetical experiment at the POWTEX [3] instrument located at the FRM-II. Herein, we want to give special emphasis to the entry ‘Instrument: configuration used, installed options’ since this should include all needed parameters for data reduction, e.g., within PowderReduceP2D function of Mantid [4], a reference to the current instrument definition file (at the time of the experiment) and also the set of fundamental instrument description (FID) parameters [5]. [1] Dronskowski, R. et al. "Neutron diffraction: a primer" Zeitschrift für Kristallographie - Crystalline Materials, vol. 239, no. 5-6, 2024, pp. 139-166. https://doi.org/10.1515/zkri2024-0001 [2] Kisi, E. H. and Howard, C. J. “Applications of Neutron Powder Diffraction” Oxford University Press, 2008. ISBN: 9780199657421. [3] Houben, A. et al. “New neutron-guide concepts and simulation results for the POWTEX instrument” Nuclear Instruments and Methods in Physics Research Section A, vol. 680, 2012, pp. 124-133. https://doi.org/10.1016/j.nima.2012.03.015. [4] Arnold, O. et al. “Mantid-Data Analysis and Visualization Package for Neutron Scattering and mu-SR Experiments”. Nuclear Instruments and Methods in Physics Research Section A, vol. 764, 2014, pp. 156-166. https://doi.org/10.1016/j.nima.2014.07.029. [5] Houben, A. et al. “POWTEX visits POWGEN“ Journal of Applied Crystallography, vol 56, part 3, 2023, pp. 633-642. https://doi.org/10.1107/S1600576723002819. Dataset Metadata Field Type Comment Usecase example or possible values for POWTEX Identifier Uuid Identifier / name Data set name Human readable name Start time Date/time Of the measurement/run, applies to file End time Date/time Of the measurement/run, applies to file Sample ID PID of sample PID (external or local ID) Data format Ideally nexus format is used Title / description Free text Short description of the measurement/run Calibration measurement with vanadium Instrument: configuration used, installed options All Keywords needed, see example description of installed options and links to any further information on the used instrument setup, e.g. detector type, detector position, neutron guide type, wavelength band - Instrument description: POWTEX IDF 2025 - Wavelength band: 1 - Pulse-Frequency frequency: 200 Hz (100, 200, 400, 480, 500, 600, 666, 800, 1000, 2000, 2200) Hz - ratio P10 chopper: 1 (1, 11/15, 33/40, 22/25, 55/60) - ratio P11 chopper: 1 (1, 10/11, 5/11, 20/33, 15/22, 21/22) - ratio OC chopper: 1/2 (0, 1/2) - ratio BC chopper: 1/2 (0, 1/2) - neutron guide changer positions: 1,1,1 (1,1,1; 1,1,0; 1,0,0; 2,2,2; 2,2,2,3) [in principle any combination of 1 = default guide; 0 = absorbing; 2 = higher reflectivity) - roof detectors: used (used/not used) - FID parameters: o Type:PN2 o fltPath:60.0 o 2-theta:90.0 o difC:22591.86 o difA:0.0 o difB:0.0 o Zero:0.0 o alpha-0:500.0 o alpha-1:1.05387 o beta-0:500.0 o beta-1:0.0 o beta-q:0.0 o sig-0:0.0 o sig-1:0.0 Metadata Field Type Comment Usecase example or possible values for POWTEX o sig-2:0.0 o sig-q:0.0 o X:0.0 o Y:0.0 o Z:0.0 o Azimuth:0.0 o pfType:8 o L2A:0.81 o L2B:0.0 o div:0.001919862 o W-Pixel:0.0 o Dtt:0.000623 o DL:0.002 o DthF:0.969 o Add:0.00148 o WSample:0.00433 o Eta:0.21 o DthDet:0.00678 o Bank:1 Measurement technique(s) Free text PaNET ontology20 if possible or free text Neutron Time-ofFlight Powder Diffraction Environment conditions / settings Key value pairs; name, value, unit as many key value pairs (or time-log series) as needed, also for automatic data processing and analysis, e.g. temperature, pressure, magnetic field Temperature, 300, K Measurement mode Keyword Identifying the free variable during the run/measurement, e.g. temperature, pressure, magnetic field, time Time Sample environment: installed options Choice of different sample environment options by keyword, free text or sample environment PID - Cryofurnace, JANIS cryostat, mirror oven, uniaxial press, free sample stage - Globular collimator: used (used, not used) Metadata Field Type Comment Usecase example or possible values for POWTEX Purpose of data set Choose between: measurement / calibration / sample / background / alignment / … calibration References Link, Identifier e.g. calibration data ID of vanadium and empty measurement Comments Free Text Add comments after the measurement, e.g. to note mistakes, failures etc. Can also be provided automatically via instrument control software Beam down after 1 h Quality metrics Free text Data quality metrics is a number given by the user to rate the dataset 10/10 Analysis status Choose between: analysis planned / analysis ongoing / analysis finished / intend to publish / published / analysis not possible / open to outside analysis Allow user to give an indication on the analysis status. If dataset cannot or will not be analyzed this can also be highlighted here. Open to outside analysis Sample Metadata Field Type Comment 1 Usecase example POWTEX Name Free text Human readable name Vanadium Local ID Ext PID Link Registration schema If externally registered Agency If externally registered Key words following e.g. PhySH Description Free text Description of sample Vanadium powder Metadata Field Type Comment 1 Usecase example POWTEX Chemical composition e.g. CAS number, SMILE, InCh V Common name Free text If applicable Vanadium State Choose between: liquid / powder / single crystal / solid / thin film / in situ Powder Mass Value, unit pair If applicable 200 mg Crystal structure Structural archetype and/or space group number according to IUCR If applicable Vanadium, I m -3 m Unit cell parameters Multiple value, unit pairs If applicable a = 3.02710 Å Preparation date Date If applicable Supplier / creator Relationships Parent sample ID If applicable Additional fields Any additional information - Sample container shape: sphere (sphere) - Sample container diameter: 10 (5, 8, 10, 12), mm - Sample container material: Vanadium (Vanadium, Glas)