Evidence for Jahn-Teller Distortions at the Antiferromagnetic Transition inLaTiO3

${\mathrm{L}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_3$ is known as a Mott insulator which orders antiferromagnetically at $T_{\mathrm{N}}=146\mathrm{K}$. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At $T_{\mathrm{N}}$ significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.