  This work reports on the pressure dependence of the octahedra tilts and mean
Fe-O bond lengths in RFeO3 (R=Nd, Sm, Eu, Gd, Tb and Dy), determined through
synchrotron X-ray diffraction and Raman scattering, and their role on the
pressure induced phase transition displayed by all of these compounds. For
larger rare-earth cations (Nd-Sm), both anti- and in-phase octahedra tilting
decrease as pressure increases, whereas the reverse behavior is observed for
smaller ones (Gd-Dy). EuFeO3 stands at the borderline, as the tilts are
pressure independent. For the compounds where the tilts increase with pressure,
the FeO6 octahedra are compressed at lower rates than for those ones exhibiting
opposite pressure tilt dependence. The crossover between the two opposite
pressure behaviors is discussed and faced with the rules grounded on the
current theoretical approaches. The similarity of the pressure-induced
isostructural insulator-to-metal phase transition, observed in the whole
series, point out that the tilts play a minor role in its driving mechanisms. A
clear relationship between octahedra compressibility and critical pressure is
ascertained.
