Measurement Details
Questions about experimental setup and data applications
What information can be obtained from amorphous samples?
For amorphous samples, we can provide comprehensive structural characterization through total scattering measurements combined with pair distribution function (TS-PDF) analysis. This technique is particularly valuable for materials lacking long-range order. The information you can obtain includes:
- Local atomic structure: Identification of short-range ordering and coordination environments around atoms
- Bond distances: Precise measurements of interatomic distances between nearest neighbors
- Coordination numbers: Determination of how many atoms surround each atom at specific distances. Note that this requires absolute scaling of the data, which requires additional normalization steps.
- Medium-range order: Structural correlations extending beyond nearest neighbors (typically in the range of approximately 10–30 Å)
- Structural domains: Detection of nano-domains or local ordering
- Phase identification: Determination if the sample is truly amorphous or contains nanocrystalline domains
- Structural evolution: When measurement are performed on samples that have undergone different synthesis or processing procedures, insights into relative structural changes can be determined
- Quantitative modeling: The data can be used for real space structure refinement such as small-box modeling, Reverse Monte Carlo modeling or other computational approaches to generate 3D structural models
- Composition-structure relationships: When comparing related compositions, understanding how composition affects local structure
- Density information: Indirect information about atomic density and microporosity
What are the benefits of synchrotron radiation with our setup?
Our high-energy X-ray setup is particularly well-suited for diffraction and scattering measurements due to:
- High Q-range coverage (up to ~30 Å-1), providing excellent real-space resolution
- Low background due to high beam collimation and effective shielding
- High signal-to-noise ratio due to high flux, high detection efficiency, and no dark current noise
- Symmetric instrumental peak shape, e.g., no axial divergence due to use of 2D area detector
- Minimal absorption effects due to high-energy X-rays
- Excellent reproducibility for comparative studies
What is the wavelength used for the measurements?
The measurements are performed using high-energy X-rays with a wavelength of approximately 0.165 Å (corresponding to an energy of about 75.0 keV). This wavelength is well-suited for powder diffraction for several reasons:
- High penetration: The short wavelength allows X-rays to penetrate deeply into samples, reducing surface effects and providing bulk information
- Minimal absorption: Reduced absorption, especially for heavy elements, leading to more accurate measurement intensities
- Large Q-range: Access to a wide range of reciprocal space in a single measurement, capturing both short and long-range structural information
- Reduced fluorescence background: For many elements, the high energy is well above the K edge, reducing fluorescence scattering
This wavelength is particularly advantageous compared to laboratory sources (typically 0.5–1.5 Å), as it can provide high quality data for a broader range of elements measured in transmission mode.
What is the difference between HR-XRPD and TS-PDF analysis?
High-Resolution X-ray powder diffraction (HR-XRPD) and total scattering pair distribution Function (TS-PDF) analysis are complementary techniques that provide different insights into material structure:
HR-XRPD:
- Focuses on long-range, periodic atomic arrangements
- Provides crystal structure information (unit cell, space group, atomic positions)
- Excellent for phase identification and quantification
- Can determine crystallite size and strain
- Best suited for crystalline materials with long-range order
TS-PDF:
- Analyzes both Bragg peaks and diffuse scattering
- Provides local structure information (bond distances, coordination)
- Works for both crystalline AND amorphous materials
- Reveals short and medium-range ordering (typically 1–30 Å)
- Can detect local distortions not visible in average structures
What are the limitations of PDF analysis using 75 keV energy?
At 75 keV, fluorescence scattering can occur for certain elements, affecting the detector's bright field response. This is particularly notable for:
- Lanthanides (especially from the second half of the series)
- Heavy elements like Hf, Ta, W, Re, Os.
While this does not significantly impact the high-resolution XRPD data for our setup, it does significantly reduce the usable Qmax for PDF measurements and decreases the accuracy of data normalization. We are working on implementing protocols to improve these cases.
For samples containing these elements, a lower Qmax-inst and Qmax value need to be used to remove enough of the artifact for the rpoly correction to work reasonably. Data still may only be suitable for qualitative analysis.
What sample environments are available?
We currently offer one standard measurement setup, which utilizes a flat plate transmission geometry using our high-throughput sample changer. See here for more details of the sample holders.
We do not use capillaries and do not currently provide temperature-dependent, in situ, or in operando measurements.
Can air-sensitive samples be measured?
How should air-sensitive samples be handled?
For air-sensitive samples, we have had success with the following approach:
- Loading in a glovebox
- Adding an extra layer of Kapton tape over the edges of the primary window
- Keeping under argon until just before measurement
- Storing the sample stick in a desiccator (or back under argon) between PDF, XRD, and SAXS runs
See here for more details.
This method has been tested with various materials including LiZrCl-type samples that remained stable for both PDF and XRD throughout the shift. Without these precautions, they transformed within 10–15 minutes. We are currently designing a new version of the holder that is formally sealed.
If your samples are air-sensitive, please indicate whether they should be handled in a glove box or if they can be stored and loaded under ambient conditions.
What is the resolution of the XRPD data?
Our HR-XRPD measurements provide high-resolution diffraction data at high energy with:
- Angular resolution (FWHM) approximately 0.005° 2θ
- Q-space resolution (ΔQ) of approximately ~0.004 Å-1 (based on first peak integral breadth)
- Real-space resolution (2π/Qmax) of approximately 0.69 Å
This high resolution allows for:
- Clear separation of closely spaced diffraction peaks
- Precise lattice parameter determination
- Accurate peak shape analysis for microstructure studies
- Detection of subtle phase transitions and symmetry changes
Can you detect trace phases in my sample?
Yes, our high-resolution setup is excellent for detecting minor phases in multiphase samples. Typically, crystalline phases present at levels of < 0.5–1wt% can be detected. Factors that affect detection limits include:
- Crystallinity: Well-crystallized minor phases are easier to detect than poorly crystalline ones
- Peak overlap: Minor phases with distinctive peaks separated from the main phase are easier to identify
- Absorption contrast: Large differences in absorption between phases can affect detection limits
- Sample homogeneity: Well-mixed samples provide more reliable quantification of minor phases
For optimal trace phase analysis, please provide information about suspected minor phases when submitting your samples.
What is the beam size used for the measurements?
The beam size used for our measurements is approximately 0.05–0.075 mm in diameter. The beam is focused on the detector position using transfocators. This minimizes beam divergence and leads to improved instrumental resolution. Despite the relatively small beam size, we are still able to achieve a good powder average for powders with crystallite sizes on the order of < 5 microns by vibrating and shaking the samples during the measurement.
Do you provide grazing incidence measurements?
Currently, we do not have the possibility to perform grazing incidence measurements. We have done transmission on polycrystalline films, although our setup is not really optimal for that either, especially for very thin films. Our setup is primarily designed for powders and bulk polycrystalline solids.
What is the experimental setup and data processing details?