Crystal Structure, Magnetic and Electrical Properties of Compounds in the RCrMnO5 Family (R = Sm, Eu, Gd, Tb, Ho and Er) Synthesized Under High Oxygen Pressure. Issue 28 (2nd September 2015) - Pomiro, Fernando
Abstract: RCrMnO5 (R = Sm, Eu, Gd, Tb, Ho, and Er) were synthesized at high O2 pressures and 900–950 °C. Crystal structures were refined by using powder X‐ray diffraction (PXRD) and powder neutron diffraction (PND) for Tb, Ho, and Er compounds and PXRD for Sm, Eu and Gd compounds. All compounds were isostructural with RMn2 O5 . By using the bond‐valence model we found that (Cr/Mn) 4+ mainly occupy the octahedral sites and (Cr/Mn) 3+ occupy the pyramidal sites. Antisite disorder between octahedral and pyramidal sites was found in the three samples analyzed by PND. From the values obtained for the occupancies of Cr and Mn in the pyramidal and octahedral sites and from the approximate average oxidation states for each crystallographic site obtained by the bond‐valence calculations, an estimated ionic distribution model was proposed. The μ eff value for RCrMnO5 could be explained by considering the contribution of all the paramagnetic species and by using the ionic distribution model. No magnetic long‐range order was observed by PND in R = Er, Ho, and Tb compounds. All the Curie–Weiss temperatures obtained from the magnetic susceptibility were negative ( θ < 0), indicating antiferromagnetic correlations. For the compounds with Eu and Sm, θ close to –200 K were obtained for the Cr–Mn sublattice. The semiconducting properties could be described by a variable range hopping mechanism associated with antisite disorder of Cr/Mn. No dielectric transitions were observed in the electric permittivity in the measured temperature range. Abstract : RCr x Mn y O5 (R = Sm, Eu, Gd, Tb, Ho, and Er) with "ideal" composition x = y = 1 where synthesized at moderate high O2 pressures. Refinement of powder neutron diffraction (PND) data allow us to obtain the "real" RCr x Mn y O5 compositions with x and y values slightly deviated from 1. The real composition allowed us to calculate the effective magnetic moments, which were in very good agreement with experimental values.