Neutron powder diffraction is a powerful technique to clarify the relationship between the crystal structures and the properties of functional materials. Since neutron atomic scattering factors do not depend on atomic numbers monotonically, neutron diffraction gives more reliable structural information than X-ray to detect light elements among heavy ones. There are more than 60 neutron powder diffractometers (NPD's) in the world. In Japan, the angle dispersive diffractometry is adopted in NPD's at JRR-3 while the time of flight diffractometry is adopted in NPD's at KENS and J-PARC. This article was written to introduce the two diffractometries and their NPD's.
