EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Materials with the DyMn2O5 structure type have immense potential for novel physical properties, but they remain largely unexplored. In this research, the isostructural SmFe1-xCrxTiO5 (x = 0-1) compounds were synthesized by the ceramic method. We thoroughly investigated their magnetic properties as well as possible photocatalytic applications. The crystal structure of these materials can be defined within the orthorhombic Pbam space group. There are three distinct crystallographic sites with different geometries: R3+ cations occupy an eight-coordination dodecahedral site, while the transition metals are distributed between octahedral and square-pyramidal sites. For a complete understanding of the structure of these materials, neutron and synchrotron x-ray diffraction experiments were carried out. The samples were also tested for photocatalytic dye degradation, to offer a possible future application.
Magnetization curves reveal that different compositions show different low-temperature transitions. SmFeTiO5 has a transition at around 55 K, which appears to move to lower temperatures with increasing Cr3+ content. This trend was also confirmed by low-temperature Mössbauer measurements. Finally, SmCrTiO5 has a different behavior, displaying a slight increase in magnetization below 175 K, followed by a more marked increase below 45 K. The differences observed in the magnetic behavior are strongly influenced by the distribution of transition-metal cations between two different crystallographic sites. To explore this distribution, Mössbauer spectroscopy measurements were conducted on the Fe-containing samples. Each spectrum was fitted with two doublets, which correspond to Fe3+ cations distributed between square-pyramidal and octahedral coordination. Cr3+ cations show a preference for the octahedral site, forcing more Fe3+ cations to move and share the square-pyramidal position with the Ti4+ cations. Raman spectroscopy measurements also confirm this trend by following the intensity decrease of the TiO5 bending and stretching peaks in samples with higher Fe content.