Key Engineering Materials Vols. 512-515

Abstract: Multiferroic ceramics, based on the ferroelectric and ferrimagnetic phases of the Pb(Zr0.65Ti0.35)O3 (PZT) and BaFe12O19 (BaM) systems, respectively, were obtained from the conventional ceramic method. The electrical properties have been investigated in a wide temperature and frequency range. The influence of the magnetic phase on the ferroelectric and dielectric properties of the ferroelectrics phases have been taken into account. The phase transition characteristics shown to be strongly affected by the amount of the BaM phase, while the dielectric properties revealed to be directly dominated by the presence of conductive effects related to the charge transport mechanisms associated to the magnetic phase.

Abstract: A series of ferroelectric superlattice films on ITO substrates have been artificially fabricated by radio frequency magnetron sputtering, starting from the PbZrO3 (PZO) and PbTiO3 (PTO) matrix targets. The design sequence of the layers has been changed via shifting sputtering target in the preparing processes. Diverse systems have been shaped and discussed by XRD, SEM and UV-Vis. UV-Vis absorption spectra have been paid more attention especially, due to the low-cost and non-destructive method to provide the information about the thicknesses of the films.

Abstract: Alkali-free barium boroaluminosilicate glass-modified PLZST antiferroelectric ceramics with glass contents between 0 and 8 wt.% have been fabricated respectively by a traditional solid phase reaction. The PLZST ceramics doped with alkali-free barium boroaluminosilicate glass showed typical antiferroelectric phase when the glass contents were below 6 wt.% and the refined grains were observed. The addition of glass decreased the dielectric constant of samples. With increasing of the glass additives, both the Curie temperature and the remanent polarization deceased. It may be that Ba₂₊ entered in the perovskite structure, which acts as an important modified ion in the alkali-free barium boroaluminosilicate glass. Larger forward antiferroelectric-ferroelectric phase transition field (E_AFE-FE >50 kV/cm) and higher breakdown strength (E_BDS ≥105 kV/cm) were displayed in glass-modified PLZST ceramics. The improvement properties of samples were benefit for energy storage which is desired for the high power energy storage capacitors and pulsed power applications.

Abstract: We demonstrated the superior electrocaloric effect (ECE) in BaTiO3 multilayer structure. The sample fabricated by tape-casting process has 120 effective ferroelectric layers with average layer thickness of 1.7 μm. The ferroelectric hysteresis loops were measured in the temperature range from 30 to 180 oC, and then the temperature dependences of ECE adiabatic temperature change and heat absorption were obtained according to Maxwell relation. A peak ECE adiabatic temperature change of 0.027 K/V and heat absorption of 0.36 J/g were observed near the ferroelectric phase transition at 125 oC under Vmax=25 V. The BaTiO3 thick film can sustain an external electric field (>500 kV/cm) several times higher than bulk ferroelectric ceramics (~30 kV/cm). Although the EC coefficient of BaTiO3 is much lower than lead-based ferroelectric ceramics, the ultrahigh working electric field endows it a large ECE, higher than that of most reported lead-based ferroelectric ceramics. In addition, the lead-free composition provides it a promising future in solid-state cooling technology.

Abstract: Results of fabrication and study of Ba_1-xLa_xTi_1-x/4O₃ (BLT) ceramics for x within the range 0.001≤x≤0.004 is reported in the present paper. BLT ceramics has a structure based on ABO₃–type perovskite, and its properties strongly depend on the chemical com_{Subscript text}position. The interrelated semiconductor and ferroelectric properties of La-doped BaTiO₃ ceramics were considered for describing its electrical properties. Dielectric properties were studied in frequency domain by impedance spectroscopy with a Quadtech 1920-type precision LCR meter at room temperature T=RT.

Abstract: The electrical properties of Pr₆O₁₁-doped bismuth titanates (Bi_xPr_yTi₃O₁₂, BPT) ceramics prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of Pr-doped samples exhibit negative differential resistance behavior. The conducting filamentary model has been used to explain the negative differential resistance phenomenon in Pr-doped bismuth titanates. The impedance spectrum indicates that Pr-doped sample consists of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi₄Ti₃O₁₂ and the distribution of every element is uniform. Pr-doped samples exhibit randomly oriented and plate-like morphology.

Abstract: We have investigated the structure and ferroelectric properties of the Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films on SiO₂/Si substrate fabricated by sol-gel method. We used the BLT films were annealed at various temperatures of 600, 650, and 700°C for one hour by conventional furnace annealing (CTA). The temperature dependence of leakage currents densities of ferroelectric BLT thin films. The crystalline structure of the prepared BLT thin films was analyzed by X-ray diffraction (XRD). Field emission scanning electron microscopy (FESEM) was used to observe the film thickness and the surface morphology including grain size and porosity. The leakage current density and capacitance of thin film were measured by HP4156C.

Abstract: In this study, the effects of La and V doping on Bi₄Ti₃O₁₂ (BLTV) ferroelectric thin films deposited on ITO/glass substrates using rf magnetron sputtering were produced and investigated. The effect of oxygen concentration and RF power on the physical and electrical characteristics of BLTV thin films was determined. The physical characteristics of BLTV thin films were obtained by the XRD pattern, SEM and AFM. The variations of crystallization, surface roughness and thickness of BLTV thin films were discussed. The electrical properties of BLTV thin films deposited under various parameters were measured by the HP4156C.

Abstract: Tb-doped bismuth titanate (Bi_xTb_yTi₃O₁₂ BTT) thin films were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique, and the microstructures and ferroelectric properties of the films were investigated. Microstructure studies indicate that all of BTT films with well-developed rod-like grains consist of single phase of a bismuth-layered structure without preferred orientation. The experimental results indicate that Tb doping into Bi₄Ti₃O₁₂ results in a remarkable improvement in ferroelectric properties. The remanent polarization ( Pr ) and coercive field ( Ec ) of the BTT film with y=0.6 were 22 μC/cm2 and 85 kV/cm, respectively. After 3 × 10¹⁰ switching cycles, 20% degradation of Pr is observed in the film.

Abstract: The electrical properties of Tb₄O₇-bismuth titanate (Bi_3.3Tb_0.6Ti₃O₁₂) prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of Tb-doped sample exhibits a simple ohmic behavior. The impedance spectrum of Tb-doped sample indicates that consist of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi₄Ti₃O₁₂ and the distribution of every element is uniform. Tb-doped sample exhibit randomly oriented and plate-like morphology.