Here we present synthetic and structural aspects dealing with the reduction of the hexagonal AMnO3 multiferroics (A= Y, Ho, Er, Tm, Yb) into original oxygen deficient phases. Previously reported topotactic reduction of YMnO3 using CaH2 leads to a series of YMnO3-x (x&lt;0.2) phases with progressive removal of basal oxygen of the initial MnO5 trigonal bipyramids. The reducing power of solid hydrides was such that these deficient phases have been considered as the most reduced forms of AMnO3, so conserving the parent AB stacking between two subsequent Mn-layers. At moderate temperature in ammonia flow, we have been able to stabilize a more reduced AMn2+O2.5 state. XRD, PND and HREM results show that a phase separation occurs into two intergrown layered sublattices with nominal compositions ∞[AMn2+O2+x](1-2x)+ and ∞[AMn2+O3-x](1+2x)- containing versatile Mn2+ coordinations. The former sublattice shows original AA stacking between Mn layers where Mn is mainly tetrahedral with additional interstitial oxygen (Oint) . In the second intergrown sublattice, the observed AB stacking is reminiscent of oxygen removal from the parent YMnO3 crystal structure and Mn conserves a deficient pyramidal coordination. The passage from AB to the original AA lattice is allowed by the conservation in the two structures of CdI2-like [YO2] layers which “hold“ the crystal structures. It is depicted in the figure 1. After a complete study of the reduction of AMnO3 phases using various gas flows and starting reactants we will present the the key-parameters for a fine control of the final phases and Mn valence state.

Long route from hexagonal-AMn3+O3 to AMn2+O2.5

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.