PHASE-DIAGRAM OF LATIOX - FROM 2D LAYERED FERROELECTRIC INSULATOR TO 3D WEAK FERROMAGNETIC SEMICONDUCTOR

LaTiO(x) compounds are structurally related to perovskites and there are two known phases. The first, x = 3.50, is a 2D layered-type ferroelectric. The second, x = 3.00, is a weak ferromagnet with a 3D orthorhombic distorted perovskite structure. 20 samples with varying oxygen stoichiometry between these end members were prepared by floating zone melting, and then characterized by means of X-ray powder diffraction, electron microscopy, thermogravimetric analysis, resistivity and magnetic measurements. A phase diagram is established which displays the following physical and structural properties. A structural phase boundary at x = 3.20 separates a new series of 2D layered structures from the 3D orthorhombic one. The former series represents the first conducting titanium oxides with a 2D layered structure to be reported. At x = 3.10 a phase boundary exists between a metallic and a weak ferromagnetic state where the magnetic transition temperature T(c) can be sensitively tuned by the oxygen stoichiometry x. Samples with T(c) between 100 K and 130 K exhibit a metal-semiconductor transition whereas samples with higher T(c), up to 149 K, are semiconductors between room temperature and 4.2 K.