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

The topotactic reduction of the acentric phase YMnO3 with CaH2 in the temperature range 225 °C < T < 350 °C yields phases of composition YMnO3−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 YMnO2.95 and YMnO2.85 adopt antiferromagnetically ordered magnetic structures with P63 and P63cm symmetries, respectively, consistent with the increased level of structural disorder in the latter phase.