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, αa and αc, with the ionic radii, rA and rB, 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 αa more than c and αc and the reverse is true for replacements in the B sites. Unequal valencies on the A and B sites affect thermal expansion coefficients, particularly αc