| Multiferroics are a class of materials which possess at least two ferroic properties among ferroelectricity, ferromagnetism (antiferromagnetism), and ferroelasticity. Due to their rich connotation in condense matter physics and attracting potential applications, multiferroic materials have become one of the hottest research topics in material science. In the present work, the microstructure, multiferroic properties, and the low temperature dielectric relaxation in BiFeO3-CaTiO3 solid solutions and Mn-modified CaTiO3 ceramics were systematically investigated, and the physical nature was discussed. The following conclusions were obtained:(Bi1-xCax)(Fe1-xTix)O3 ceramics with x= 0.1,0.15,0.2,0.3,0.4,0.6 and 0.8 were prepared by the solid state process, and the dielectric, ferroelectric and magnetic properties were evaluated together with the crystal structures. The single-phase (Bi1-xCax)(Fe1-xTix)O3 solid solutions are obtained by introducing CaTiO3 because of the increased structural stability, where the symmetry changes from R3c (x≤0.2) to Pbnm (x≥0.3). The improved multiferroic characteristics are achieved in the present ceramics, and reaches best properties at x= 0.2. The present ceramics show more regular P-E hysteresis loop with Pr～0.28μC/cm2 for x= 0.2 under an electric field of 40 kV/cm and frequency of 100 Hz. The M-H hysteresis loop with Mr= 0.26 emu/g and Hc= 6.74 kOe is observed in the sample with x= 0.2 at 5 K, which suggests that the present modified ceramics have weak ferromagnetism due to the replacement of Fe3+ time to time by Ti4+ destroying its previous spiral structure to allow the appearance of a macroscopic magnetization. The present results suggest a new candidate for multiferroic material with the enhanced properties.More compositions were prepared to investigate its low temperature dielectric properties. For (Ca1-yBiy)(Ti1-yFey)O3 (y= 0.2,0.4,0.6,0.7,0.8,0.85,0.9) ceramics, when y≤0.7, a relaxor dielectric peak appeared at the low temperatures and they were well fitted with the Barrett equation. With increasing BiFeO3 content, the peak moves to higher temperature, the dielectric constant and the intensity of the peak improves. Two sets of dielectric relaxations are observed When y≥0.8. The higher temperature relaxor peak may be related with the point defection, and the lower temperature peak obeys Vogel-Fulcher relation well which implies the relaxor ferroelectricity. This implies the transition from incipient ferroelectric to relaxor ferroelectric, which improves the transition temperature and the ferroelectricity of the samples greatly.Meanwhile, the dielectric and multiferroic properties of Ca(Ti1-xMnx)O3 (x= 0.025.0.05) ceramics were also investigated. Single samples have been obtained through a solid state process, which presented in space group of Pbnm. It is not available for getting single phase and evaluating its ferroelectric properties when the content of Mn increases due to the fact that it improves the leakage and loss of the ceramics. Decreasing temperature can suppress the leakage greatly and get more regular P-E loops. The samples are paramagnetic without any ferromagnetism transition. |
PDF Full Text Request