Structures and Magnetism of La_1–<i>x</i>Sr_<i>x</i>MnO_{3–(0.5+<i>x</i>)/2} (0.67 ≤ <i>x</i> ≤ 1) Phases

Abstract

Topotactic reduction of La1–xSrxMnO3 (0.67 ≤ x ≤ 1) phases with sodium hydride yields a series of isoelectronic materials of composition La1–xSrxMnO3–(0.5+x)/2. Lanthanum rich members of the series (0.67 ≤ x ≤ 0.83) adopt anion deficient perovskite structures with a 6-layer -OTOOT′O- stacking sequence of sheets of octahedra/square-based pyramids (O) and sheets of tetrahedra (T). The strontium rich members of the series (0.83 ≤ x ≤ 1) incorporate “step defects” into this 6-layer structure in which the OTOOT′O stacking sequence is converted into either OOTOOT′ or TOOT′OO at a defect plane which runs perpendicular to the [201] lattice plane. The step defects appear to provide a mechanism to relieve lattice strain and accommodate additional anion deficiency in phases with x > 0.83. Magnetization and neutron diffraction data indicate La1–xSrxMnO3–(0.5+x)/2 phases adopt antiferromagnetically ordered states at low-temperature in which the ordered arrangement of magnetic spins is incommensurate with the crystallographic lattice.