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Peterson, Peter F.

Publications and source records attributed to Peterson, Peter F..

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Time-of-flight neutron total scattering with applied electric fields: Ex situ and in situ studies of ferroelectric materials

Characterizing the structural response of functional materials (e.g., piezoelectrics and ferroelectrics) to electric fields is key for the creation of structure-property relationships. Here in this paper, we present a new sample environment and data reduction routines which allow the measurement of time-of-flight neutron total scattering during the in situ or ex situ application of high voltage (<10 kV) to a sample. Instead of utilizing the entire detector space of the diffractometer, only selected regions of detector pixels with scattering at the desired angle to the sample electric field are interrogated, which allows the generation of orientation-dependent reciprocal space patterns and real-space pair distribution functions (PDFs). We demonstrate the method using the relaxor ferroelectric Na 1/2 Bi 1/2 TiO 3 and observe lattice expansion parallel and contraction perpendicular to the electric field for both in situ or ex situ experiments, revealing the irreversible nature of the local scale structural changes to this composition. Additionally, changes in the distributions of nearest neighbor metal-oxygen bond lengths are observed, which have been difficult to observe in previously measured analogous orientation-dependent X-ray PDFs. Lastly, considerations related to sample positioning and background subtraction are discussed, and future research directions are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Advances in utilizing event based data structures for neutron scattering experiments

This article strives to expand on existing work to demonstrate advancements in data processing made available using event mode measurements. Most spallation neutron sources in the world have data acquisition systems that provide event recording. The new science that is enabled by utilizing event mode has only begun to be explored. In the past, these studies were difficult to perform because histograms forced dealing with either large chunks of time or a large number of files. With event based data collection, data can be explored and rebinned long after the measurement has completed. This article will review some of the principles of event data and how the method opens up new possibilities for in situ measurements, highlighting techniques that can be used to explore changes in the data. We also demonstrate the statistical basis for determining data quality and address the challenge of determining how long to measure mid-measurement. Lastly, we demonstrate a model independent method of grouping data via hierarchical clustering methods that can be used to improve calibration, reduction, and data exploration.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Event-based processing of neutron scattering data at the Spallation Neutron Source

Here, the Spallation Neutron Source at Oak Ridge National Laboratory, USA, ushered in a new era of neutron scattering experiments through the use of event-based data. Tagging each neutron event allows pump–probe experiments, measurements with a parameter asynchronous to the source, measurements with continuously varying parameters and novel ways of testing instrument components. This contribution will focus on a few examples. A pulsed magnet has been used to study diffraction under extreme fields. Continuous ramping of temperature is becoming standard on the POWGEN diffractometer. Battery degradation and phase transformations under heat and stress are often studied on the VULCAN diffractometer. Supercooled Al 2 O 3 was studied on NOMAD. A study of a metallic glass through its glass transition was performed on the ARCS spectrometer, and the effect of source variation on chopper stability was studied for the SEQUOIA spectrometer. Besides a summary of these examples, an overview is provided of the hardware and software advances to enable these and many other event-based measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Combinatorial appraisal of transition states for in situ pair distribution function analysis

In situ total scattering measurements are increasingly utilized to follow atomic and nanoscale structural details of phase transitions and other transient processes in materials. This contribution presents an automated method and associated tool set to analyze series of diffraction and pair distribution function data with a linear combination of end-member states. It is demonstrated that the combinatorial appraisal of transition states (CATS) software tracks phase changes, relative phase fractions and length scales of interest in experimental data series. Here it is further demonstrated, using a series of local structure data simulations, that the misfit of such a model can reveal details of phase aggregation and growth related to the pair distribution function's sensitivity to interphase correlations. CATS may be applied to quantitative evaluation of many transient processes, including amorphous-to-crystalline phase transitions, the evolution of solid-solution behaviors, the precipitation and growth of aggregates, and other atomic to nanoscale details of crystallization and phase transformation phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Erratum: “A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials” [Rev. Sci. Instrum. 88, 034101 (2017)]

We report that in the original paper,1 the following chemical formula was reported erroneously: Na 78-2x Ca x Al 78 Si 144 O 384 , x ≈ 38. The correct formula for the material studied is Na 86-2x Ca x Al 86 Si 106 O 384 , x ≈ 43. The difference in formula values between this corrected composition and values in Table 1 has no effect on the refinement quality (within the reported error), the subsequent analysis, or overall conclusions of the manuscript. Specifically, the neutron diffraction data and crystallographic refinement are insensitive (within the reported error) to the corresponding change in the Si/Al ratios, and the corrected number of Ca (x ≈ 43) is found to be within the error of the value reported via crystallographic refinement of the Ca occupancy [x = 46(3)].

36 MATERIALS SCIENCE↗
DOE OSTI2017

A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials

Gas-solid interfaces enable a multitude of industrial processes, including heterogeneous catalysis; however, there are few methods available for studying the structure of this interface under operating conditions. Here, we present a new sample environment for interrogating materials under gas-flow conditions using time-of-flight neutron scattering under both constant and pulse probe gas flow. Outlined are descriptions of the gas flow cell and a commissioning example using the adsorption of N 2 by Ca-exchanged zeolite-X (Na 78–2x Ca x Al 78 Si 144 O 384 ,x ≈ 38). We demonstrate sensitivities to lattice contraction and N 2 adsorption sites in the structure, with both static gas loading and gas flow. A steady-state isotope transient kinetic analysis of N 2 adsorption measured simultaneously with mass spectrometry is also demonstrated. In the experiment, the gas flow through a plugged-flow gas-solid contactor is switched between 15 N 2 and 14 N 2 isotopes at a temperature of 300 K and a constant pressure of 1 atm; the gas flow and mass spectrum are correlated with the structure factor determined from event-based neutron total scattering. As a result, available flow conditions, sample considerations, and future applications are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Event-Based Processing of Neutron Scattering Data

Many of the world's time-of-flight spallation neutrons sources are migrating to the recording of individual neutron events. This provides for new opportunities in data processing, the least of which is to filter the events based on correlating them with logs of sample environment and other ancillary equipment. This paper will describe techniques for processing neutron scattering data acquired in event mode that preserve event information all the way to a final spectrum, including any necessary corrections or normalizations. This results in smaller final errors, while significantly reducing processing time and memory requirements in typical experiments. Results with traditional histogramming techniques will be shown for comparison.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The NeXus data format

NeXus is an effort by an international group of scientists to define a common data exchange and archival format for neutron, X-ray and muon experiments. NeXus is built on top of the scientific data format HDF5 and adds domain-specific rules for organizing data within HDF5 files, in addition to a dictionary of well defined domain-specific field names. The NeXus data format has two purposes. First, it defines a format that can serve as a container for all relevant data associated with a beamline. This is a very important use case. Second, it defines standards in the form of application definitions for the exchange of data between applications. NeXus provides structures for raw experimental data as well as for processed data.

97 MATHEMATICS AND COMPUTING↗