Dielectric and magnetic properties of (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 ceramics prepared by high energy mechanochemical technique

Abstract

Multiferroic (Bi 1-x La x FeO 3 ) 0.5 (PbTiO 3 ) 0.5 ceramics with x = 0, 0.1, 0.2, 0.3 and 0.5 was prepared from mechanochemically synthesized nanopowders. The XRD studies revealed the tetragonal structure for x≤0.2 and rhombohedral for x=0.5 with mean grain sizes from 15 to 28 nm. Dielectric response of the compounds in the temperature range 125-525 K was found to contain two anomalies: at~400 K attributed to the presence of oxygen vacancies and that below 300 K characteristic of ferroelectric relaxors; the Curie point anomaly was apparent at 500 K only for samples with x=0.5. Analysis of the low-temperature response enabled us to characterize the relaxor state of the solid solution and to yield information on the decrease in the activation energy of dipole moment flipping in polar nanoregions. Magnetic studies revealed two contributions to the magnetization of the nanoceramics pointing to a coexistence of weak ferromagnetic and antiferromagnetic orderings in the range 4÷300 K. Low temperature variation of the magnetization in field-cooling and zero-field-cooling conditions revealed spin glass behavior which in (Bi 1-x La x FeO 3 ) 0.5 (PbTiO 3 ) 0.5 is dependent on x. Moreover, a sharp step in magnetization at~250 K was found to be dependent on the La content and related to the A-site distortion leading to a modification of Fe-O-Fe angles and antiferromagnetic coupling between magnetic Fe 3+ moments.

Structural modification and evaluation of Dielectric, Magnetic and Ferroelectric Properties o f Nd- modified BiFeO3– PbTiO3 Multiferroic Ceramics

“…The values of magnetization of ZFC plots at low temperature are found to be 0.00841emu/g, 0.01292emu/g, 0.031.29emu/g and 0.089.41emu/g for(BNFPT) x compound with x = 0.05, 0.10, 0.15 and 0.20 respectively. We found the better result of magnetization with Nd doping as compared to other reports on rare earth doped or undoped BF-PT compounds [39,40]. The enhancement in magnetization demonstrates that Nd doped bismuth ferrite, of course, affects the Fe-O-Fe angles and thus has a major effect on its magnetic ordering.…”

“…Furthermore, silver electrodes were applied to the sintered and polished pellets in order to conduct polarization hysteresis loop and leakage current versus voltage characterization (Radiant Technologies). [20,39]. Impurities and secondary phases were not observed in the diffraction pro les, which indicates in corporation of Nd +3 in (BNFPT) x crystal framework and con rms crystallinity of the compositions.…”

Electric Conductivity of (Bi1-xLaxFeO3)0.5(PbTiO3)0.5Ceramics Obtained from Mechanosynthesized Nanopowders

“…As the compounds of BFO with PbTiO 3 exhibit structural change from rhombohedral to tetragonal structure [8] and La 3+ doping may turn the structure again to the rhombohedral symmetry [1,11], we prepared The results of the Raman spectroscopy studies of the obtained nanopowders pointed to a change in the crystallographic structure of the BLFOPT solutions with Lacontent between x = 0.16 and x = 0.20 [23]. Our dielectric response studies revealed also relaxor-like behavior below 300 K in ceramics prepared from the mechanosynthesized nanopowders due to structural disorder, an anomaly at ≈ 400 K related to oxygen vacancies and only for solution with x = 0.50 the Curie point anomaly at ≈ 500 K was observed [24]. Moreover, a coexistence Figure 3 shows frequency dependences of the conductivity and dielectric permittivity for samples in the La-content range where the changes in the Raman spectra have been observed [23].…”