The topotactic reduction of the acentric phase YMnO3 with CaH2 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 P63 and P63cm symmetries, respectively, consistent with the increased level of structural disorder in the latter phase.
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