Neutron-diffraction study of the temperature factors of LaSn3

Neutron-diffraction techniques have been used to study in detail the intensities of the superlattice reflections in La${\mathrm{Sn}}_3$. We find that the thermal motion of the Sn atoms is highly anisotropic, in agreement with lattice-dynamical calculations. Analysis of the experimental results by the introduction of fourth-order anharmonic terms suggests that such higher-order terms may be of importance in determining the temperature factors of the Sn atoms in La${\mathrm{Sn}}_3$.