Thermal Expansion of Compounds of Zircon Structure

The thermal expansion behavior of 13 members of ABO 4 compounds of the zircon family is examined in terms of crystal chemical (size, charge, and mass of cations) and crystallographic ( a and c ) parameters. The systematic trend in the thermal expansion coefficients, α a and α c , with the ionic radii, r A and r B , can be explained in terms of the unique arrangement of M‐O polyhedra along a and c directions of this lattice. In the zircon structure, edge‐sharing ZrO 8 dodecahedra form a chain along the a direction while the chain along the c direction consists of alternate edgesharing SiO 4 tetrahedra and ZrO 8 triangular dodecahedra. Substitution in the A sites affects a and α a more than c and α c and the reverse is true for replacements in the B sites. Unequal valencies on the A and B sites affect thermal expansion coefficients, particularly α c .