B-site disordering in Ba3Ln2MoO9 (Ln=Ho, Er) perovskites: A neutron diffraction study

We describe the preparation, structure determination and magnetic properties of two Ba perovskites containing rare-earth cations at the B-sublattice. Ba3Ln2MoO9 (Ln=Ho3+ and Er3+) were synthesized by ceramic procedures. Joint X-ray (XRPD) and neutron (NPD) powder diffraction refinements were carried out to analyse the crystal structure. At room temperature, both phases are tetragonal, space group I4/mcm, Z=4. Ln and Mo atoms are found to be distributed at random over the octahedral sites of the perovskites. Magnetic measurements at 0.1 T show that both samples are paramagnetic between 3 and 300 K, following a Curie–Weiss law. M vs. H curves show a region of paramagnetic behaviour and above 2.5 T a magnetic saturated system is observed. Finally, the temperature evolution of the NPD patterns of Ba3Ho2MoO9 reveals the absence of long-range magnetic ordering down to 2 K.