Powder neutron diffraction study of the thermal expansion of a K-substituted cordierite

Abstract

A structural study of a potassium-substituted cordierite with K_0.5Mg₂Al_4.5Si_4.5O₁₈ formula was performed between 20 and 825° C using a time-of-flight powder neutron diffraction technique, on sintered samples obtained by glass crystallization. The thermal evolution of this compound is essentially of the same nature as for pure hexagonal cordierite, but is very dependent on the presence of potassium atoms within the channels. The very low value of the thermal expansion coefficient ($\bar \alpha = 0.4 x 10^{ - 6} K^{ - 1}$ between 20 and 825° C) results from an opposite evolution of thea andc lattice parameters which may be explained in terms of a reorganization and a regularization of (Al, Si)O₄ and MgO₆ polyhedra. It strongly depends on the Al/Si ordering degree.