Structure de SnPb2O4 à quatre températures: relation entre dilatation et agitation thermiques

The structural study of SnPb₂O₄ oxide, an isomorphic compound belonging to the general family “MeX₂O₄” like Pb₃O₄, is made from accurate X-ray and neutron diffraction techniques on powdered samples. The structural evolution of SnPb₂O₄ is analyzed from 300 to 5 K: no phase transition is observed, contrary to Pb₃O₄, which exhibits a tetragonal → orthorhombic transition at 170 K. The thermal expansion tensor is practically isotropic in this temperature range: the α_a, α_c and α_V coefficients are neighboring those observed in the Pb₃O₄ tetragonal phase at the same temperature. On the other hand, the thermal vibrations are strongly anisotropic, with large amplitudes in the (a, b) plane. In this study the thermal vibrations are connected to the thermal expansion. $\text{B}\text{ab}$ and $\text{B}\text{c}$ temperature factors are considered as functions of the a and c cell parameters. The relation established by Grüneisen between the mean-square amplitudes of vibrations and the thermal volume expansion is discussed. The interatomic distances found show that the bindings are similar to that of Pb₃O₄: only the Sn⁴⁺O₆] octahedrons are smaller than Pb⁴⁺O₆] octahedrons.