The science
From average structure to local structure
Powder diffraction provides detailed information about the average periodic structure of crystalline materials. Total-scattering measurements contain both Bragg and diffuse-scattering contributions. PDF analysis uses suitably reduced total-scattering data to investigate local and medium-range pair correlations in real space.
Science at a glance
Average structure, local structure
What each level of analysis describes, and where the method emphasis shifts.
Powder X-ray diffraction (PXRD)
Average structure
When X-rays or neutrons interact with a crystalline powder, the periodic arrangement of atoms produces a powder diffraction pattern containing Bragg reflections and, depending on the material and experiment, diffuse-scattering contributions. Peak positions support phase identification, while quantitative phase analysis uses full-pattern intensities and appropriate models to estimate phase fractions. Rietveld refinement can refine lattice parameters and, where the data quality and structural model support it, parameters such as atomic positions, occupancies and displacement parameters. Powder diffraction is widely used for phase identification, quantitative phase analysis and crystallographic refinement of crystalline materials.
Wider applications
What ANALISA can do
Phase identification · Quantitative phase analysis · Rietveld refinement · Full-pattern analysis
Explore Powder Diffraction Analysis →Total scattering & PDF
Local structure
Total-scattering measurements contain both Bragg and diffuse-scattering contributions. Rietveld refinement primarily models the Bragg component to describe the average periodic structure, whereas PDF analysis uses suitably reduced total-scattering data to access real-space pair correlations. After appropriate data reduction and Fourier transformation, the pair distribution function, G(r), provides access to local and medium-range structural information that may not be captured by an average crystallographic model. Interpretation still requires structural modelling and awareness of data-reduction and instrumental effects.
Electrode local structure
PDF analysis can probe local structural changes associated with cation ordering, nano-phase formation, anion-redox-related structural changes and lithium storage in cathode and anode materials, often in combination with complementary measurements, including operando measurements through charge/discharge cycling.
Nanoscale structure
For nanostructured and poorly crystalline materials, conventional average-structure models may become insufficient to describe finite-size effects, local distortions and structural disorder. PDF analysis provides real-space pair-correlation information that can complement conventional crystallography, particularly when combined with complementary methods.
Polymorphs & amorphous content
PDF analysis can support polymorph discrimination and investigations of local order and amorphous components in pharmaceutical formulations prepared via milling, dehydration, compaction or quench cooling.
A common structural framework
Correlated disorder can leave characteristic signatures in diffraction and total-scattering data. PDF analysis provides a useful structural framework for comparing local correlations across glasses, framework materials, complex oxides, relaxor ferroelectrics and other structurally disordered materials.
What ANALISA can do
PDF generation & validation · Local-structure modelling · RMC / big-box modelling · Comparison of structural hypotheses
Explore PDF & Total Scattering →How we choose the method
How the analysis is selected
The scientific question determines the analysis, not the other way round.
Question
What structural information do you actually need?
Data
What was measured, and at what resolution and quality?
Method
PXRD, total scattering, PDF, diffuse scattering or advanced modelling, chosen to fit the scientific question and the available data.
Model
Structural modelling and interpretation — the appropriate model depends on dataset quality, resolution, Q-range and the scientific question.
Interpretation
What structural conclusions are supported by the data, what depends on modelling assumptions, and what remains uncertain?
Evidence vs. assumption
What the data can support
We distinguish between what the data directly constrain, what requires structural modelling assumptions, and what remains uncertain. The aim is not simply to obtain a good fit, but to identify which structural interpretations are supported by the available evidence.
From data to deliverable
Typical outputs
Sound familiar?
What can ANALISA help you find?
Data rescue
Your experiment may already be finished.
The data may still contain structural information that was never extracted.
ANALISA Materials can assess previously collected diffraction and scattering datasets and determine whether additional analysis — including Rietveld refinement, PDF analysis, structural modelling or comparison of structural hypotheses — can answer new scientific questions.
Have a dataset? Tell us what you want to learn.
Request an Analysis →