Synthesis, structure, and properties of La_1-xSr_xTiO₃ (0 < x < 1)

The search for a new superconductor in an early transition metal oxide prompted the investigation of the La_1-xSr_xTiO₃ series of compounds. The solid solution La_1-xSr_xTiO₃ (0 ≤ x ≤ 1) has been prepared by arc melting stoichiometric amounts of SrTiO₃ and LaTiO₃. Single-phase samples can be made for the entire stoichiometry range. The polycrystalline samples have been characterized using microprobe, thermogravimetric analysis, powder X-ray and neutron diffraction, temperature-dependent magnetization, and dc resistivity. The compounds crystallize in the orthorhombic space groups Pbnm (x ≤ 0.30) and Ibmm (0.30 < x < 0.80), and the cubic space group Pm3m (x ≥ 0.80). The Pbnm structure exists in two forms, O′-orthorhombic (x < 0.10) and O-orthorhombic (0.10 ≤ x ≤ 0.30), which are a result of Jahn-Teller distortion. The samples x = 0.00, 0.05 are canted antiferromagnets which exhibit a net ferromagnetic moment below 150 K and temperature-independent magnetism from 150 to 300 K. All other compositions show temperature-independent magnetism from 160 to 300 K with some samples (x ≥ 0.50) displaying paramagnetism in the low-temperature range. The temperature dependent resistivity measurements show that the samples are metallic (x ≤ 0.70) and semiconducting (x = 0.90). The x = 0.80 sample undergoes a semiconductor-metal transition. The properties of these materials are discussed in reference to the phenomenological phase diagram for perovskites proposed by Goodenough and high-T_c superconductivity.