Influence of Topotactic Reduction on the Structure and Magnetism of the Multiferroic YMnO₃

The topotactic reduction of the acentric phase YMnO 3 with CaH 2 in the temperature range 225 °C < T < 350 °C yields phases of composition YMnO 3− x ( x = 0 < x < 0.2). Oxide ions are deintercalated from the equatorial anion sites of the material, which induces increasing levels of structural disorder into the resulting phases, ultimately leading to the adoption of a centrosymmetric structure by x = 0.2. Variable-temperature X-ray diffraction measurements indicate a lowering of the “ferroelectric” transition temperature with increasing anion vacancy concentration, consistent with the structural data. Low-temperature neutron diffraction data show YMnO 2.95 and YMnO 2.85 adopt antiferromagnetically ordered magnetic structures with P 63 and P 63 cm symmetries, respectively, consistent with the increased level of structural disorder in the latter phase.