Qiu-Xiang Liu

Energy-storage properties and high-temperature dielectric relaxation behaviors of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics

(1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0, 5, and 10 mol%) ceramics were prepared using a conventional mixed oxide solid state reaction method. The low-temperature relaxor behavior of (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics were examined in the temperature range from 120 to 523 K. A broad dielectric maximum that shifted to higher temperatures with increasing frequency, signified the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ = 1.61–1.94 estimated from the linear fit of the modified Curie–Weiss law indicated the relaxor nature. High-temperature dielectric relaxation phenomena were found in the temperature region 600–850 K. Energy-storage properties were also analyzed, and the energy-storage density calculated from hysteresis loops reached about 0.47 J cm−3 at room temperature.

Dielectric relaxation and pinning phenomenon of (Sr,Pb)TiO3 ceramics for dielectric tunable device application.

The behavior of ferroelectric domain under applied electric field is very sensitive to point defects, which can lead to high temperature dielectric relaxation behaviors. In this work, the phases, dielectric properties and ferroelectric switching behavior of strontium lead titanate ceramics were investigated. The structural characterization is confirmed by X-ray diffraction. The high dielectric tunability and high figure of merit of ceramics, especially Sr0.7Pb0.3TiO3 (SPT), imply that SPT ceramics are promising materials for tunable capacitor applications. Oxygen vacancies induced dielectric relaxation phenomenon is observed. Pinched shape hysteresis loops appeared in low temperature, low electric field or high frequency, whereas these pinched hysteresis loops also can become normal by rising temperature, enhancing electric field or lowering frequency. The pinning and depinning effect can be ascribed to the interaction between oxygen vacancies and domain switching. A qualitative model and a quantitative model are used to explain this phenomenon. Besides, polarization and oxygen treated experiment can exert an enormous influence on pinning effect and the machanisms are also discussed in this work.

Preparation of Magnetic Ni0.5Co0.5Fe2O4 Nanoparticles and their Applications In Adsorption of Bovine Serum Albuminn

Ni0.5Co0.5Fe2O4 (NCFO) nanoparticles were prepared by the chemical co-precipitation process using metal chloride, nitrate and acetate as precursor, after the precursors were annealed and then investigated in detail by employing X-ray diffraction (XRD), magnetic measurement and the bovine serum albumin (BSA) adsorption on the nanoparticles was analyzed by UV spectrophotometer at room temperature. XRD analysis indicates that all the as-prepared nanocrystals posses a pure cubic spinel structure. The saturation magnetization initially increases and then decreases with increasing annealing temperature, with a maximum value 67.19 emu/g at 950 °C. The coercivity also firstly increases and then decreases with increasing annealing temperature, with a maximum value of 828 Oe at 650°C. The as-prepared Ni0.5Co0.5Fe2O4 nanoparticles exhibit a good adsorbing ability for BSA and the optimized adsorption is achieved for the Ni0.5Co0.5Fe2O4 nanoparticles annealed at 750°C with grain size about 33.3 nm.

Influence of SrTiO3 Buffer Layer on the Ferroelectric Properties of Bi2NiMnO6 Thin Film

Double perovskite Bi2NiMnO6 (BNMO) thin films with and without SrTiO3 (STO) buffer layer have been prepared on Pt (111)/Ti/SiO2/Si(100) substrates by a chemical solution deposition method. The microscopic surface morphology, ferroelectric, and leakage current have been investigated. It is shown that the STO buffer layer can improve the remnant polarization slightly, and reduce the coercive electric field from 100 to 36 kV/cm. When the positive voltage was applied on top Au electrode of the BNMO/STO/Pt thin film capacitors, the leakage current was controlled by ohmic conduction. When the negative voltage was applied on bottom Pt electron, the leakage current of BNMO/STO thin film was limited by the traps and the density of carriers at high electric field.

Enhanced electrocaloric analysis and energy-storage performance of lanthanum modified lead titanate ceramics for potential solid-state refrigeration applications

The unique properties and great variety of relaxer ferroelectrics make them highly attractive in energy-storage and solid-state refrigeration technologies. In this work, lanthanum modified lead titanate ceramics are prepared and studied. The giant electrocaloric effect in lanthanum modified lead titanate ceramics is revealed for the first time. Large refrigeration efficiency (27.4) and high adiabatic temperature change (1.67 K) are achieved by indirect analysis. Direct measurements of electrocaloric effect show that reversible adiabatic temperature change is also about 1.67 K, which exceeds many electrocaloric effect values in current direct measured electrocaloric studies. Both theoretical calculated and direct measured electrocaloric effects are in good agreements in high temperatures. Temperature and electric field related energy storage properties are also analyzed, maximum energy-storage density and energy-storage efficiency are about 0.31 J/cm3 and 91.2%, respectively.

Giant negative electrocaloric effect in B-site non-stoichiometric (Pb0.97La0.02)(Zr0.95Ti0.05)1+yO3 anti-ferroelectric ceramics

ABSTRACT A negative electrocaloric effect (ECE) in B-site non-stoichiometric (Pb0.97La0.02)(Zr0.95Ti0.05)O3 antiferroelectric ceramics synthesized by the conventional solid-state reaction method is investigated via indirect and direct measurements. Temperature-dependent P-E hysteresis loops were measured. A giant negative electrocaloric temperature change of about 12.45 K was achieved. The results indicate that the antiferroelectric ceramics with non-stoichiometry modification could be a promising candidate for the applications in cooling devices. IMPACT STATEMENT Giant negative electrocaloric effect (NECE) was achieved in B-site non-stoichiometric PLZT2/95/5 ceramics, the NECE parameters are comparable or even larger than most of the reported bulk materials, making it attractive for cooling devices application. GRAPHICAL ABSTRACT

Influence of LaNiO 3 and LaNi 0.5 Mn 0.5 O 3 Buffer Layers on the Structural and Electrical Properties of BiNi 0.5 Mn 0.5 O 3 Thin Films

The structural and electrical properties of BiNi0.5Mn0.5O3/LaNi0.5Mn0.5O3 (BNM/LNM) and BiNi0.5Mn0.5O3/LaNiO3 (BNM/LNO) heterostructure thin films fabricated on Pt/Ti/SiO2/Si(100) substrates by a chemical solution deposition method were studied. The x-ray diffraction results indicated that polycrystalline hexagonal perovskite structures were formed. It was found that the electrical properties of the heterostructure thin films were obviously different from each other. For the Au/BNM/LNM/Pt structure, slightly distorted ferroelectric hysteresis loops were observed and the leakage current density versus applied electric voltage curves at positive and negative biases were asymmetrical. The conduction mechanism was dominated by an ohmic conduction mechanism at positive bias, whereas at negative bias, the conduction mechanism was dominated by the ohmic conduction mechanism, trap-filled-limit (TFL) conduction, and grain-boundary-limited behavior. However, for the Au/BNM/LNO/Pt structure, slim hysteresis loops with no distortion were observed and the leakage current was approximately four orders of magnitude lower than that of Au/BNM/LNM/Pt. The conduction mechanisms were controlled mainly by an ohmic conduction mechanism, TFL conduction, and grain-boundary-limited behavior at positive and negative biases.

Dielectric Property of 0.45NiFe2O4+0.55BaTiO3 Ceramic Composites

The standard double sintering ceramic method was used to prepare the 0.45NiFe2O4 +0.55BaTiO3 composites. Complex impedance analysis enables us to separate the contributions from grain and grain boundary in the samples. Impedance spectroscopy measurements were conducted in a frequency range from 20 Hz to 2 MHz and in a temperature range from 75 to 200°C. The impedance measurements have also shown the evidence of grain boundary conduction and lowering of barrier to the motion of charge carriers with rise in temperature. We also found that the relaxation frequency shift to high side with increase in temperature.