Crystal and magnetic structure of LaTiO3 : evidence for non-degenerate $t_{2g}$-orbitals

The crystal and magnetic structures of LaTiO 3 have been studied by x-ray and neutron-diffraction techniques using nearly stoichiometric samples. We find a strong structural anomaly near the antiferromagnetic ordering T N = 146 K. In addition, the octahedra in LaTiO 3 exhibit an intrinsic distortion, which implies a splitting of the t 2 g levels. Our results indicate that LaTiO 3 should be considered as a Jahn-Teller system where the structural distortion and the resulting level splitting are enhanced by the magnetic ordering.