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

F. POMIRO; J. LOHR; ELISA V. PANNUNZIO MINER; V. NASSIF; R.D. SÁNCHEZ; R.E. CARBONIO

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2015 vol. 2015 p. 4737 - 4749

1434-1948

RCrMnO 5 (R = Sm, Eu, Gd, Tb, Ho, and Er) were synthesized at high O 2 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 RMn 2 O 5 . 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 dis-order between octahedral and pyramidal sites was found in the three samples analyzed by PND. From the values ob tained 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  temperaturesobtained from the magnetic susceptibility were negative (θϽ 0), indicating antiferromagnetic correlations. For the com-pounds with Eu and Sm, θ close to ?200 K were obtained forthe Cr?Mn sublattice. The semiconducting properties couldbe described by a variable range hopping mechanism associ-ated with antisite disorder of Cr/Mn. No dielectric transitionswere observed in the electric permittivity in the measuredtemperature range.