Effect of BF-based content on phase formation, microstructure, electric and magnetic properties of BNKLT, KNLNTS and BCTZ ferroelectric ceramics

Abstract

In this study, the effect of Bi2FeCrO6 and Bi0.8Ba0.2FeO3 on phase formation, microstructure, electric and magnetic properties of BNKLT, KNLNTS and BCTZ ferroelectric ceramics synthesized by the solid-state combustion technique using glycine as fuel has been investigated.

Firstly, lead free solid solution Bi0.5(Na0.68K0.22Li0.10)0.5TiO3-xmol%Bi2FeCrO6 (BNKLT-xBFCO), with x=0, 0.004, 0.007, 0.013 and 0.019, ceramics were calcined at 750oC and sintered at 1150oC for 2 h using the solid state combustion technique. The effect of the x content on the phase formation, microstructure, electric and magnetic properties of the produced ceramics were investgated. All samples exhibited a pure perovskite phase with the co-existence of rhombohedral and tetragonal phases. The doping of BFCO enhanced the density and dielectric properties of the BNKLT ceramics. The BNKLT-0.013BFCO ceramics showed the highest density (5.87 g/cm3), excellent dielectric properties (εR~1390, tan δR~0.039, εm ~4986 and tan δm~0.075) and the highest piezoelectric constant (d33~194 pC/N). The sample with x=0 showed diamagnetic behavior, while the samples with 0.004-0.019 content exhibited paramagnetic behavior with higher magnetization at higher x content.

Secondly, (1-x)Bi0.5(Na0.77K0.20Li0.03)0.5TiO3-xBi0.8Ba0.2FeO3 ((1-x)BNKLT-xBBF) ceramics with x=0-0.4 were synthesized by the solid state combustion technique. The X-ray diffraction pattern of the ceramics showed a pure perovskite structure with the co-existence between the rhombohedral and tetragonal phases. From the Rietveld refinement, we observed that the unit cell volume increased as x increased due to the replacement of Bi3+ and Ti4+ ions by Ba2+ and Fe3+ ions at A-site and B-sites, respectively. The average grain size and measured density increased with increasing x. The resistivity of (1-x)BNKLT-xBBF ceramics decreased with increasing x. At room temperature, the (1-x)BNKLT-xBBF ceramics with x=0.2-0.4 exhibited multiferroic behavior characterized by ferroelectric and ferromagnetic hysteresis loops. The highest relative density (95.48%), the highest dielectric constant and low dielectric loss at room temperature (εR=1746 and tan δR=0.0296), good ferroelectric properties (Pr=6.46 μC/cm2 and Ec=11.84 kV/cm) and good ferromagnetic properties (Mr=0.002 emu/g and Hc=110 Oe) were obtained from the 0.8BNKLT-0.2BBF ceramic, indicating that this sample has potential for applications in lead free, room temperature multiferroic systems.

Thirdly, (1-x)[(K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3]-xBi0.8Ba0.2FeO3 [(1-x)KNLNTS-xBBF] lead-free ceramics, with different x content, were prepared by the solid-state combustion technique. The effect of Bi0.8Ba0.2FeO3 content on the phase formation, microstructure, electric and magnetic properties of KNLNTS ceramics were investigated. The KNLNTS ceramic exhibited co-existing orthorhombic and tetragonal phases. When x increased, the samples demonstrated an increased tetragonal phase and unit cell volume. The average grain size, density and relative density deceased when x increased up to 0.06 and then continuously increased. For x=0, a well saturated P-E loop was found which the Pr and Ec values were about 21.27 μC/cm2 and 12.38 kV/cm, respectively. While, x=0.02-0.2 exhibited round P-E loop because the leakage current were performed. For higher x, the leakage current of the samples decreased, suggesting that the samples exhibiting slim P-E loops. The KNLNTS ceramic exhibited diamagnetic behavior while the x=0.02-0.4 samples showed ferromagnetic behavior. At room temperature, multiferroic behavior, which exhibited fair ferroelectric and ferromagnetic hysteresis loops, were obtained from the samples with x=0.3-0.4 which means these ceramics can be applied in multifunctional devices.

Finally, lead free (1-x)Ba0.85Ca0.15Ti0.90Zr0.10O3-xBi0.80Ba0.20FeO3 [(1-x)BCTZ-xBBF] ceramics, with BBF content (x) between 0-0.4 [0, 0.02, 0.06, 0.1, 0.2, 0.3, 0.4], were prepared via the solid-state combustion technique. The effect of BBF content on the phase formation, microstructure, electric and magnetic properties of BCTZ was studied. From the Rietveld refinement analysis, the BCTZ ceramic showed co-existing orthorhombic and tetragonal phases, with a ratio of 35.4:64.6 and the percentage of the tetragonal phase continuously increased when x increased from 0.02 to 0.1, and became purely tetragonal at x≥0.2. When x increased, the average grain size, density and relative density continuously decreased while the unit cell volume enlarged. The dielectric constant at room temperature (εR) tended to decrease while the dielectric loss at room temperature (tan δR) increased with increased BBF content. For x=0, a pure BCTZ ceramic, a well saturated P-E loop was observed with a polarization (Pr) and coercive field (Ec) of 8.94 μC/cm2 and 4.06 kV/cm, respectively. The ferroelectricity drastically decreased with x=0.02. For x≥0.06, the leakage current increased, which suppressed the ferroelectricity. With no BBF content (x=0) the ceramic had diamagnetic properties, that changed to paramagnetic properties with x=0.02-0.06 and finally to ferromagnetic properties when the BBF increased between 0.10-0.40. For x=0.10-0.40, the remnant magnetization (Mr) continuously increased.

In summary, the factor of chemical composition, phase formation, microstructure, and electrical property of each system are important to the induce magnetic property. The optimum composition of BNKLT-0.013BFCO, BNKLT-0.2BBF, KNLNTS-0.3BBF and BCTZ-0.1BBF ceramics were observed which is effective way to improve the properties of these ceramics for various applications such as reading/writing with magnetization, spintronic, energy harvesting or sensors.

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