The evolution of the structural properties of (Formula presented) was determined as a function of temperature, average (Formula presented)-site radius (Formula presented) and applied pressure for the “optimal” doping range (Formula presented) 0.30, by using high-resolution neutron powder diffraction. The metal-insulator transition, which can be induced both as a function of temperature and of (Formula presented) was found to be accompanied by significant structural changes. Both the paramagnetic charge-localized phase, which exists at high temperatures for all values of (Formula presented) and the spin-canted ferromagnetic charge-ordered phase, which is found at low temperatures for low values of (Formula presented) are characterized by large metric distortions of the (Formula presented) octahedra. These structural distortions are mainly incoherent with respect to the space-group symmetry, with a significant coherent component only at low (Formula presented) These distortions decrease abruptly at the transition into the ferromagnetic metal phase. These observations are consistent with the hypothesis that, in the insulating phases, lattice distortions of the Jahn-Teller type, in addition to spin scattering, provide a charge-localization mechanism. The evolution of the average structural parameters indicates that the variation of the electronic bandwidth is the driving force for the evolution of the insulator-to-metal transition at (Formula presented) as a function of “chemical” and applied pressure. © 1997 The American Physical Society.
Materials by design for sustainable solutions in the energy, medical, transport, and engineering sectors
