  Thermal expansion is a problem in many technological applications and its
control represents a challenge in materials design. In this Letter, after
studying the correlation between thermal expansion, cubic-to-rhombohedral
transition and lattice parameter of ReO3-type structures, I show how in the
different methods for controlling thermal expansion the key element is actually
the lattice parameter. By varying the lattice parameter through external
pressure, chemical modifications or other methods, the single-well potential
energy of the octahedral rotation, responsible for Negative Thermal Expansion
(NTE), can be turned into a quartic anharmonic potential or into a double-well
potential, thus enhancing or suppressing the NTE, respectively. This result can
be extended to other framework-structures and should be taken into account to
overcome the challenge of controlling thermal expansion.
