Search

Lead-free piezoelectric ceramics of Ba0.70Ca0.30Ti1−x Fe x O3 (x=0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x≤0.02 are diphasic composites of tetragonal Ba0.80Ca0.20TiO3:Fe and orthorhombic Ba0.07Ca0.93TiO3:Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x=0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128°C to 58°C. However, the ferroelectricity enhances slightly and reaches the maximum near x=0.005, and then weakens with increasing x. On the other hand, the piezoelectric coefficient (d 33) and the electromechanical coupling coefficient (k p ) decrease simultaneously with increasing x, whereas the mechanical quality factor (Q m ) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO3-based lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Sr2Fe1−0.5x Mo1−0.5x Ir x O6 ceramics (x=0, 0.02, 0.04, 0.06, and 0.08) have been synthesized and the structures, magnetic and transport properties have been investigated. X-ray diffraction reveals a very low solution limit of x=0.06, which however, results in significantly decreased Fe/Mo ordering degree and thus decreased magnetization value. On the other hand, the Curie temperature (T c) rises from 390K (x=0) to 400K (x=0.02) firstly, and then decreases to 360K and 340K for the compositions with x=0.04 and 0.06, respectively. In addition, the resistivity and magnetoresistance drop drastically with increasing x. The composition with x=0 shows semiconductor transport behavior in the temperature range of 10–400K, whereas the other compositions show a minimum resistivity around 120K. These results are discussed in detail by considering the effects of Ir substitution. [Copyright &y& Elsevier]

Abstract: The effects of sintering temperature and poling conditions on the electrical properties of tetragonal and orthorhombic diphasic Ba0.70Ca0.30TiO3 (BCT) lead-free ceramics have been systematically investigated. On the one hand, with increasing sintering temperature from 1270°C to 1400°C, the bulk density increases monotonically and the Curie temperature keeps almost constant with the value of ∼120°C, whereas the grain size, the maximum relative dielectric constant, room temperature polarization reach the maximum values for samples sintered at 1340°C. On the other hand, it is found that the piezoelectric property depends on poling electric field and poling temperature significantly. An enhanced piezoelectric behavior of d 33=126pC/N, k p =0.29, and Q m =588 is obtained for the BCT ceramics poled at 100°C with 30kV/cm field for 20min. The aging behavior of the piezoelectric property is also investigated. [Copyright &y& Elsevier]

Abstract: The microstructure and electric properties of the rhombohedral–tetragonal morphotropic phase boundary (MPB) composition 0.8Bi1/2Na1/2TiO3–0.2Bi1/2K1/2TiO3 have been investigated. X-ray and electron diffraction results substantiate the co-existence of tetragonal and rhombohedral phases. The ferroelectric domains were clearly observed by electron microscopy. The oxygen octahedron tilting of the samples was studied by SAED. Both saturated polarization–electric field and butterfly shaped strain–electric field hysteresis loops prove that the MPB composition shows typical ferroelectric nature. The detailed microstructure–property characterization may shed light on the physical property of further work on BNT–BKT around morphotropic phase boundary. [Copyright &y& Elsevier]

Abstract: Electron-doped Ba1−x La x PbO3 (x≤0.30) ceramics have been prepared; the phase, microstructure, and conductivity have been investigated as functions of x value and sintering temperature. The solution limit is close to x=0.15. Sintering temperature plays an important role in determining phase purity and microstructure (grain size and porosity). All single-phase ceramics show metallic nature, which is related to two main factors. On the one hand, electron-doping increases the resistivity from 10−8 Ωm for the composition with x=0 to 10−5 Ωm for others with x≠0. On the other hand, the effect of grain size and porosity on resistivity is considerable, though not as significant as that of electron-doping. The structure–property relationship is discussed in detail. Our results may be helpful for further work on BaPbO3-based materials. [Copyright &y& Elsevier]

Abstract: Triple perovskite Sr3MFeMoO9 (M=Mn, Co, Ni) ceramics have been prepared under flowing N2 steam. All compositions are single phase and have B-site cation ordering. However, the composition with M=Co shows denser microstructures with smaller grains, the average grain sizes are 700, 500 and 650nm for M=Mn, Co, and Ni, respectively. The chemical states of the surface and interior Mn, Co, Ni, Fe, and Mo cations are analyzed carefully. Both the magnetization-magnetic field curves and magnetization–temperature curves confirm that all compositions show antiferromagnetic behaviors. The Néel temperature of M=Mn and Ni compositions are determined to be 24.4 and 49.5K, respectively. However, M=Co composition shows two magnetic transition temperatures at 70.9 and 180.7K, which is possibly attributed to that the Co cations have intermediate spin-state (3d 6, S=1) and high spin states (3d 6, S=2). Furthermore, the compositions show semiconductor-like behaviors and neglectable magnetoresistance in whole measuring temperature range. Our results may be helpful for designing novel magnetic materials and for understanding magnetic couplings in triple perovskites. [Copyright &y& Elsevier]

Abstract: High quality double perovskite Sr2Fe10/9Mo8/9O6 thin films have been prepared on (111)-SrTiO3 substrates under different N2 partial pressures (0.1–20Pa). The films are (111)-oriented with flat surfaces and sharp film/substrate interfaces. The epitaxy and local Fe/Mo ordering are revealed by high resolution transmission electron microscopy and selected area electron diffraction. It is established that the N2 pressure has significant effects on structures and properties: With increasing N2 pressure, the film thickness decreases and the strain increases, while the magnetization decreases monotonously. Interestingly, all the films show semiconductor-like behavior in the whole measuring temperature range but the resistivity increases with increasing N2 pressure. The observed results are attributed to that N2 pressure can affect the strain and the concentration of Fe–O–Mo, both play important roles in magnetic interaction, and thus affect the magnetic and transport behaviors. [Copyright &y& Elsevier]

Abstract: Double perovskite Sr2CrWO6 films have been prepared on SrTiO3 (111) substrates by pulsed laser deposition in high vacuum (10−5 Pa). X-ray diffraction patterns indicate that the films are (111)-oriented. Both atomic force microscopy (AFM) and cross-section transmission electron microscopy (TEM) images prove that the films have very smooth surfaces. Detailed microstructures given by high resolution transmission electron microscopy (HRTEM) further confirm that the films are epitaxial with sharp and coherent substrate/film interface. Well saturated magnetization–magnetic field hysteresis loop is observed with the saturation magnetization of 1.2μB/formula unit at 10K. The films show metallic transport behavior and large positive magnetoresistance (∼180% at 10K). The structure–property relationship is discussed in detail. [Copyright &y& Elsevier]

Abstract: Lead-free piezoceramics of (1− x)Ba0.8Sr0.2TiO3–xBiAlO3 [(1− x)BST–xBA (0≤ x ≤0.12)] have been synthesized and the structures and properties have been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit is close to x =0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases exists near x =0.02. The ferroelectricity weakens monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain–electric field curves. The temperature dependent properties of the composition with x =0.02 have been typically investigated, showing that with increasing temperature, the ferroelectricity tends to be weakened. Pure electrostrictive effect has been found in the compositions with x =0.02 and 0.03 close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed. [Copyright &y& Elsevier]