Effects of Nd and Co co-doping on phase,microstructure and ferromagnetic properties of bismuth ferrite ceramics

In this work, the samples of Bi_0.95Nd_0.05Co_xFe_1?xO₃ (BNFCO) with x=0, 0.03, 0.05 and 0.07 mol fraction, were prepared by a solid state reaction. The effect of Nd and Co co-doping concentration on phase, densification, microstructure and ferromagnetic properties were examined. The BNFCO powders were prepared using a mixed-oxide method and calcined at 800 °C for 2 h before being pressed and sintered at various temperatures in the range of 825–900 °C for 2 h. An increase in Co co-doping content increased density of the ceramics. Phase analysis by X-ray diffraction indicated the existence of rhombohedral phase for all BNFCO powders and ceramics. Microstructural investigation using the scanning electron microscope showed a reduction of grain size with increasing Co content. Magnetic hysteresis loops showed that remanent magnetization and coercive magnetic field of the Co-doped samples were improved.     

Dielectric properties,electric-field-induced polarization and strain behavior of Lead Zirconate Titanate-Strontium bismuth Niobate ceramics

The dielectric properties and electric-field-induced polarization and strain behavior of (1-x)PZT-xSBN (x ranged from 0 to 1.0 weight fraction) ceramics prepared by a conventional mixed-oxide method were investigated. The dielectric properties indicated that the dielectric constant of PZT could be enhanced with small addition of SBN (x = 0.1). From the polarization hysteresis loop measurements, it was found that the ferroelectric properties of nominal PZT-SBN ceramics changed strongly from the normal ferroelectric in PZT-rich ceramics to the paraelectric character in SBN-rich compositions. The strain hysteresis loops of nominal PZT-SBN under bipolar electric field loading suggested that the butterfly curve was observed in some compositions (0 ≤ x ≤ 0.3 and pure SBN ceramic). This research clearly showed the significance of SBN in controlling the electrical properties of nominal PZT-SBN ceramics.     

Effects of dysprosium oxide addition in bismuth sodium titanate ceramics

This research focuses on the preparation and characterization of dysprosium-doped bismuth sodium titanate (BNT) ceramics. The compounds were prepared using the conventional mixed-oxide method. The amount of dysprosium oxide used was varied from 0 to 2 at.%. The mixed powders were calcined at 800 °C and checked for phase purity using X-ray diffraction technique. The powders were then cold-pressed into small pellets which were subsequently sintered at 1050 °C for 2 h. The results from density measurement and SEM micrographs showed that highly dense and high-purity ceramics were obtained. The grain size of Dy-doped samples was found to decrease with increasing Dy content. Compared to pure BNT, the addition of Dy₂O₃ in BNT ceramics slightly increased the dielectric constant values near room temperature. In addition, the Dy doping resulted in a more diffused transition temperature, less frequency dependence of the dielectric constant and very low values of the dielectric loss.     

The effect of morphotropic phase boundary on dielectric properties of Bi0.5Na0.5Ti1−xZrxO3 solid solutions

Lead-free bismuth sodium titanate zirconate (Bi_0.5Na_0.5Ti_1?xZr_xO₃ or BNTZ) solid solutions with varied composition of x=0.50, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, 0.73, 0.75 and 0.78 mol fraction were obtained using a conventional mixed-oxide method. XRD analysis indicated that the increase in concentration of Zr led to compositions across morphotropic phase boundary region. A quantitative structural investigation was carried out using the X-ray powder diffraction data. The rhombohedral phase was found to dominate for x<0.68 with space group R3c. In the morphotropic phase boundary (MPB) region i.e. 0.68≤x≤0.75, it was demonstrated that coexistence of rhombohedral and orthorhombic phase was observed. For x=0.78, the phase was completely orthorhombic with space group Pmna. Furthermore, the dielectric properties showed some enhanced activity of dipole movement at MPB boundaries which supported the presence of MPB region in this material system.     

Structure–property relations of ferroelectric BaTiO3 ceramics containing nano-sized Si3N4 particulates

Barium titanate/silicon nitride (BaTiO₃/xSi₃N₄) powder (when x = 0, 0.1, 0.5, 1 and 3 wt%) were prepared by solid-state mixed-oxide method and sintered at 1400 °C for 2 h. X-ray diffraction result suggested that tetragonality (c/a) of the BaTiO₃/xSi₃N₄ ceramics increased with increasing content of Si₃N₄. Density and grain size of BaTiO₃/xSi₃N₄ ceramic were found to increase for small addition (i.e. 0.1 and 0.5 wt%) of Si₃N₄ mainly due to the presence of liquid phase during sintering. BaTiO₃ ceramics containing such amount of Si₃N₄ also showed improved dielectric and ferroelectric properties.     

Effects of Mn-dopant on phase,microstructure and electrical properties in Bi3.25La0.75Ti3O12 ceramics

Lanthanum-doped bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂ or BLT) is important ferroelectric materials for FeRAMS, which need further improved by substituting isovalent cations to assist the elimination of defects such as oxygen vacancy. In this work, fabrication and investigation of substituting Mn⁴⁺ for Ti⁴⁺ ion on B-site of Bi_3.25La_0.75Ti₃O₁₂ ceramics were carried out. X-ray diffraction patterns of BLTMn ceramics indicated orthorhombic structure with lattice distortion, especially for samples with higher concentration of MnO₂ dopant. Microstructural investigation showed that all ceramics composed mainly of plate-like grains. An increase in MnO₂ doping content increased diameter and thickness of grains but reduced density of the ceramics. Electrical conductivity was found to decrease while dielectric constant increased with Mn⁴⁺ doping concentration.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.