Reduction of the Jahn-Teller distortion at the insulator-to-metal transition in mixed valence manganites

The insulator-to-metal transition in the manganite La0.52Y0.15Ca0.33MnO3 (T-IM approximate to 115 K) has been studied by high-resolution neutron powder diffraction. The cell volume contraction at the Curie point is accompanied by a remarkable decrease of the Jahn-Teller distortion in MnO6 octahedra. The change of the Mn-O bond lengths at T-IM is anisotropic and brings about a drop out of the basal-plane collective distortion mode Q(2), proposed to be the deformation responsible for the band split of e(<g(i)over bar>) orbitals. This is consistent with the double-exchange picture, and precludes simple ferromagnetic exchange.