Thermal Expansion of Compounds of Zircon Structure

The thermal expansion behavior of 13 members of ABO₄ 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 ZrO₈ dodecahedra form a chain along the a direction while the chain along the c direction consists of alternate edgesharing SiO₄ tetrahedra and ZrO₈ 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.