A high resolution neutron diffraction study of the perovskite LaTiO3

LaTiO3 shows a transition from temperature-independent paramagnetism to antiferromagnetism at 125 K. The temperature coefficient of the electrical resistivity changes at the same temperature from positive (i.e. metal-like) to negative (i.e. semiconductor-like). The crystal structure of LaTiO3 was investigated at five temperatures from 298 K to 10 K by time-of-flight neutron diffraction to look for any structural origin to the above phenomena. Analysis of the 298 K data confirm and improve on an existing X-ray structure determination in Pbnm. The same orthorhombic cell and space group are consistent with the data at all temperatures studied. The cell constants show anisotropy as b and c decrease with temperature and a increases slightly. There are no significant changes in Ti-O bond lengths or Ti-O-Ti angles with temperature. In the La-O polyhedron the eight nearest-neighbour bond distances decrease with decreasing temperature while the next four increase demonstrating a tendency to eightfold coordination. There is no structural anomaly of any significance near 125 K. This is not inconsistent with an itinerant antiferromagnetic model for the transition.