Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1−x)1−zO6

Perovskite-type cobaltates in the system La2Co1+z(MgxTi1−x)1−zO6 were studied for z=0≤x≤0.6 and 0≤x<0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 °C. The space group symmetry of the structure changes from P21/n via Pbnm to R3¯c with both increasing Mg content and increasing Co content. The La2Co(MgxTi1−x)O6 (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0≤x≤0.5 a linear decrease in the L3/(L3+L2) Co–L2,3 edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co2+ ion content.

Graphical abstractXRPD patterns for perovskite compounds along the lines La2Co(MgxTi1−x)O6 and La2Co1+z(Mg0.5Ti0.5)1−zO6.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights►Tuning of the oxidation state of Co in the perovskite system La2Co1+z(MgxTi1−x)1−zO6, z=0≤x≤0.6 and 0≤x<0.9. ►XANES study of the oxidation state of Co in the perovskite system La2Co1+z(MgxTi1−x)1−zO6, z=0≤x≤0.6 and 0≤x<0.9. ►Phase relations in the perovskite system La2Co1+z(MgxTi1−x)1−zO6, z=0≤x≤0.6 and 0≤x<0.9. ►Magnetic properties in the perovskite system La2Co1+z(MgxTi1−x)1−zO6, z=0≤x≤0.6 and 0≤x<0.9.