**6. Neutron diffraction**

Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. The sample is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of the structure of the material. The technique is similar to XRD but due to the different scattering properties of neutrons versus X-rays complementary information can be obtained.

A neutron diffraction measurement requires a neutron source (e.g. a nuclear reactor or spallation source), a sample (the perovskite to be studied or in general any material), and a detector. Sample sizes are large compared to those used in XRD. The technique is therefore mostly performed as powder diffraction. At a research reactor other components such as crystal monochromators or filters may be needed to select the desired neutron wavelength. Some parts of the setup may also be movable. At a spallation source the time of flight technique is used to sort the energies of the incident neutrons (higher energy neutrons are faster), so no monochromator is needed, but rather a series of aperture elements synchronized to filter neutron pulses with the desired wavelength.

Neutron diffraction is closely related to XRD. In fact the single crystal version of the technique is less commonly used because currently available neutron sources require relatively large samples and large single crystals are hard or impossible to come by for most materials. Future developments, however, may well change this picture. Because the data is typically a 1D powder pattern they are usually processed using Rietveld refinement. In fact the latter found its origin in neutron diffraction (at Petten in the Netherlands) and was later extended for use in XRD.

One practical application of elastic neutron scattering/diffraction is that the lattice constant of perovskites and other crystalline materials can be very accurately measured. Together with an accurately aligned micropositioner a map of the lattice parameters through the

Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. The sample is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of the structure of the material. The technique is similar to XRD but due to the different scattering properties of neutrons versus X-rays complementary information can be

A neutron diffraction measurement requires a neutron source (e.g. a nuclear reactor or spallation source), a sample (the perovskite to be studied or in general any material), and a detector. Sample sizes are large compared to those used in XRD. The technique is therefore mostly performed as powder diffraction. At a research reactor other components such as crystal monochromators or filters may be needed to select the desired neutron wavelength. Some parts of the setup may also be movable. At a spallation source the time of flight technique is used to sort the energies of the incident neutrons (higher energy neutrons are faster), so no monochromator is needed, but rather a series of aperture elements

Neutron diffraction is closely related to XRD. In fact the single crystal version of the technique is less commonly used because currently available neutron sources require relatively large samples and large single crystals are hard or impossible to come by for most materials. Future developments, however, may well change this picture. Because the data is typically a 1D powder pattern they are usually processed using Rietveld refinement. In fact the latter found its origin in neutron diffraction (at Petten in the Netherlands) and was later

One practical application of elastic neutron scattering/diffraction is that the lattice constant of perovskites and other crystalline materials can be very accurately measured. Together with an accurately aligned micropositioner a map of the lattice parameters through the

synchronized to filter neutron pulses with the desired wavelength.

Fig. 12. Diamond Light Source (UK).

**6. Neutron diffraction** 

extended for use in XRD.

obtained.

material can be derived. This can easily be converted to the stress field experienced by the compound. This has been used to analyze stresses in aerospace and automotive components to give just two examples. There is a good number of facilities all over the world offering a neutron source. Among them, we could mention, for instance, ISIS in the UK, and ILL in France.

Figure 13 shows a picture of the reactor hall at ILL in Grenoble, France. ILL (Institut Laue-Langevin) is one the most important centres in the world to carry out neutron experiments.

Fig. 13. Inside the reactor hall at ILL in Grenoble (France).
