Crystal Chemistry and Magnetic Properties of Gd-Substituted Aurivillius-Type Bi5FeTi3O15 Ceramics

Aurivillius-phase ferroelectrics can be turned into multiferroic materials by incorporating magnetic ions. The four-layer Aurivillius-type system Bi5FeTi3O15 is well-known to show a strong magnetoelectric effect; however, much controversy exists on its magnetic state and the possible multiferroicity at room temperature. In this paper, we report a detailed investigation on the interconnections between crystal chemistry and magnetic properties of Bi5FeTi3O15 ceramics chemically modified by the A-site gadolinium substitution. The structural studies showed that all Bi5-xGdxFeTi3O15 (0 <= x <= 1) samples adopt the polar orthorhombic space group symmetry A2(1)am at room temperature. The unit cell volume and the orthorhombic distortion decrease alongside the reduction of octahedral tilts by increasing the amount of Gd added. The decrease in tilting distortion of the [Ti/Fe]O-6 octahedra was further evidenced by the suppression of the Raman A(1)[111] tilt mode at 233 cm(-1). By using superconducting quantum interference and vibrating sample magnetometry, it was demonstrated that all the ceramics are paramagnetic from 5 K up to 700 K. It was thus concluded that the A-site substitution of Bi5FeTi3O15 with magnetic Gd ions brings about a slight structural relaxation of the parental orthorhombic lattice, but it is not an effective way to induce multiferroic properties in the Aurivillius compound. We suggest that the room-temperature (ferri/ferro/antiferro-) magnetism in Bi5FeTi3O15 previously reported in the literature might be due to the presence of magnetic impurities or local short-range magnetic ordering formed during material processing under different conditions.