The presence of superlattice reflections and detailed analysis of the powder neutron and x-ray diffraction data reveals that La rich BLF-PT (BFO0.50–LF0.50)0.50–(PT)0.50 has a ferroelectric rhombohedral crystal structure with space group R3c at ambient condition. Impedance spectroscopy, dielectric spectroscopy is subset of impedance spectroscopy and ac conductivity measurements were performed in the temperature range 483 K ≤ T ≤ 573 K to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near TcFE. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range (1 kHz ≤ f ≤ 10 MHz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneity in the sample and cause broad frequency dependent dielectric transitions. The Maxwell-Wagner model fits very well up to ∼105 Hz. Enhancement in dielectric constant and remnant polarization values are possibly due to space charge polarization caused by piling of charges at the interface of grain and grain boundaries.

The structure and physical properties such as magnetization, heat capacity, and dielectric constant of the polycrystalline Ba3NbFe3Si2O14 have been studied in detail. It is found to be structurally similar to the single crystal and also has a similar antiferromagnetic transition at TN∼26 K. The heat capacity measured in the temperature range 5 K–300 K also shows a single peak at 26 K in agreement with the magnetic behavior. The dielectric constant measured both as a function of temperature and frequency, 10 Hz to 1 MHz however exhibits two clear peaks in the temperature ranges, 20 K–35 K, and 40 K–125 K, which are dispersive in nature. Both the peaks are found to be coupled to the magnetic order with the high temperature peak signaling the onset of magnetic order while the low temperature peak signifies the completion of magnetic order. The dispersion behavior is similar to that observed in relaxor ferroelectrics wherein formation of polar nano-regions affects the relaxation dynamics.

No abstract

No abstract

Combining ferroelectricity and magnetism in the same material remains a challenge because it involves complex crystal chemistry and stringent symmetry requirements. In conventional ferroelectrics, the polarization arises from the second-order Jahn–Teller effect associated with cations of d0 or s2 lone pair electronic configuration. In contrast, the magnetism arises from cations with partially filled d or f electrons. Materials that incorporate these two kinds of cations in different crystallographic sites exhibit multiferroic properties but with weak coupling between magnetism and ferroelectricity. On the other hand, a strong cross-coupling occurs in some materials, where specific spin structures induce weak ferroelectricity below the magnetic ordering temperature. In this article, we discuss a new class of multiferroics where the polar distortion results from chemical ordering. These polar oxides are mainly pyroelectric in the entire temperature range and exhibit magnetoelectric coupling below the magnetic ordering temperatures.