Powder Instrument For Transition In Structure Investigations (PITSI)
The Powder Instrument for Transition in Structure Investigations (PITSI)—meaning “zebra” in Sesotho—is a medium-resolution neutron powder diffractometer located at Necsa’s SAFARI-1 research reactor.
PITSI is used to investigate crystallographic structures, chemical phases and magnetic phenomena in solid and powdered polycrystalline materials. Its specialised sample environments enable in-situ studies across a wide temperature range.
Capabilities
Neutron powder diffraction complements conventional X-ray diffraction by offering:
- Sensitivity to atomic nuclei rather than electron density
- Sensitivity to light elements in the presence of heavier elements
- The ability to distinguish between certain neighbouring elements in the periodic table
- Strong diffraction data at large scattering angles, without the form-factor reduction associated with X-rays
- Sensitivity to unpaired electrons, enabling the investigation of magnetic structures and phase transitions
- High penetration depth for non-destructive bulk analysis
- In-situ studies under changing temperature, pressure, magnetic-field or chemical conditions
- Investigation of energy-storage materials, including lithium-ion batteries
Applications
PITSI supports research involving, but not restricted to, the following:
- Identification and quantification of crystallographic phases
- Determination of crystal structures and lattice parameters
- Investigation of structural phase transformations
- Characterisation of magnetic ordering
- Determination of magnetic and crystallographic transition temperatures
- Rietveld analysis of multiphase materials
- Quantification of retained austenite in heat-treated steels
- In-situ temperature-dependent studies of materials
Technical Specifications
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Instrument parameters |
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Si Monochromator |
(331) |
(551) |
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λ at 2θM = 90° |
1.76 Å |
1.07 Å |
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Beam size [mm] |
Variable slits: Hor: 5 – 15 Ver: 5 – 48 |
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Temperature sample environments [K] |
Vacuum furnace: 400 < T < 1800 Bottom-loader cryostat: 4.5 < T < 320 Top-loader cryofurnace: 1.5 ≤ T ≤ 800 |
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Sample mounting |
4-Position sample changer |
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Detector |
614 mm (hor. ) × 375 mm (ver.) Oscillating radial collimator Range: 10° ≤ 2θ ≤ 115° |
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Flux at sample position |
~ 106 neutrons cm-2s-1 |
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Resolution |
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Example Investigations
- Structural phase transformations: PITSI has been used to study phase transformations in pure iron during heating. The measurements identified the transition from alpha ferrite to austenite, determined the transition temperature and measured associated changes in lattice parameters.
- Magnetic phase transitions: In-situ measurements of a chromium-rhenium alloy were used to characterise its magnetic ordering and determine its Néel temperature. The reduction in the intensity of the chromium magnetic reflection during heating indicated the suppression of antiferromagnetic behaviour. (Neutron diffraction study of the Cr84.7Re15.3 allo;BS Jacobs, ARE Prinsloo, AM Venter, ZN Sentsho, AJ Studer and CJ Sheppard)
- Multiphase materials: Rietveld analysis of neutron diffraction data has enabled the identification and quantification of multiple phases in complex oxide materials. Neutron measurements provide valuable information at large diffraction angles that may be less prominent in equivalent X-ray diffraction data as shown in the inset.
- Retained austenite: PITSI has been used to quantify retained austenite in heat-treated ferritic steel where conventional X-ray diffraction (inset) predominantly detected the ferrite phase.
Data Processing and Analysis
Initial data reduction is performed with Scan Manipulator, custom-developed software available at: https://github.com/Deon-Marais/ScanManipulator
Further analysis may be conducted using software such as TOPAS, GSAS-II or FullProf. Instrument scientists assist users with experimental planning, data reduction, structural refinement and interpretation.
Referencing PITSI
Users publishing results obtained with PITSI should reference:
A.M. Venter, P.R. van Heerden, D. Marais, J.C. Raaths and Z.N. Sentsho, “PITSI: The neutron powder diffractometer for transition in structure investigations at the SAFARI-1 research reactor,” Physica B: Physics of Condensed Matter, 551 (2018), 422–425. https://doi.org/10.1016/j.physb.2017.12.017
Instrument Scientists
Dr Zeldah Sentsho
PhD Metallurgical Engineering
Email: Zeldah.Sentsho@necsa.co.za
Telephone: +27 (0)12 305 5918
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Prof. Andrew Michael Venter
PhD Physics
Email: Andrew.Venter@necsa.co.za
Telephone: +27 (0)12 305 5038
Apply for Beam Time
Prospective users should contact an instrument scientist to discuss project feasibility, sample requirements and instrument availability. The completed Beam Time Request Form must be submitted to the instrument scientist and the BLC User Office at UserOffice@necsa.co.za.