[en] Highlights: • The composite ceramics have much higher energy storage density than pure anti-ferroelectrics. • SPS process can suppress the diffusion behavior between the tetragonal and orthorhombic phases. • A high recoverable energy storage density of 6.40 J/cm"3 was obtained in the composite ceramics. - Abstract: Anti-ferroelectric composite ceramics of (Pb_0_._8_5_8Ba_0_._1La_0_._0_2Y_0_._0_0_8)(Zr_0_._6_5Sn_0_._3Ti_0_._0_5)O_3-(Pb_0_._9_7La_0_._0_2)(Zr_0_._9Sn_0_._0_5 Ti_0_._0_5)O_3 (PBLYZST-PLZST) have been fabricated by Spark Plasma Sintering (SPS) method. The effect of SPS process on phase structure, anti-ferroelectric and energy storage properties of the composites has been investigated in detail. The X-ray diffraction, field emission scanning electron microscopy and energy-dispersive spectrometry analysis illustrate that the composites are composed of tetragonal perovskite, orthorhombic perovskite and small amount of non-functional pyrochlore phases. Compared with conventional solid-state sintering (CS) process, SPS process is helpful to suppress the diffusion behavior between the tetragonal PBLYZST and orthorhombic PLZST phases, and thereby improve the contribution of PLZST phase to the FE-to-AFE phase transition electric field (E_A) of the composites. As a result, the SPS composite ceramics possess a considerable E_A of 162 kV/cm and a high recoverable energy storage density valued 6.40 J/cm"3 which is 1.75 J/cm"3 higher than that of the CS samples and about 2.3 times as that of the PBLYZST ceramics

[en] The resistance versus time curves of room temperature unload ageing, high temperature unload ageing and high temperature continuous load test ageing of PTC thermistors are measured. At the initial aging stage under both high temperature unload ageing and high temperature continuous load test ageing, the resistance decreases first, and then increases, which are different from that of the room temperature aging. Such abnormal phenomena exist in the initial ageing stage and are attributed to buffering of the unstable mechanical stress and desorption of the absorbed oxygen molecules under the thermal action. R-T characteristic curves of aged sample are different from that of oxidized and reduced samples. A new mechanism is proposed to interpret the aging characteristics of the donor-doped BaTiO₃ PTC thermistor

[en] SiO₂-doped Ba_0.85Sr_0.15TiO₃ (SBST) glass-ceramic (g-c) films with perovskite structure have been prepared on Pt/Ti/SiO₂/Si substrates by sol-gel technique. Differential thermal analysis (DTA), X-ray diffraction (XRD) and atomic force microscopy (AFM) are employed to analyze the synthesize process and microstructure of SBST g-c films. The ferroelectricity and crystallization behavior of SBST films are discussed. It is found that the starting synthesize temperature of SBST15 film is larger than that of pure barium strontium titanate (BST) film for about 60 deg. C. The grain sizes decrease and the ferroelectricity of SBST g-c films is degenerated, but their loss tangent and leakage current density decrease with increasing SiO₂ contents. The temperature coefficient of dielectric (TCD) and the pyroelectric coefficient γ of the films are measured. The results show that TCD and the pyroelectric coefficient γ of SBST5 film at 20-25 deg. C are, respectively, 4.6% deg. C^-1 and 8.1x10^-8 C cm^-2 K^-1, which is about 2/3 value of the pure BST films. BST g-c film with 5 mol% SiO₂ dopant is hopeful to be the advanced candidate material for uncooled infrared focal plane arrays (UFPAs) applied at near room temperature

[en] Highlights: • A combinative method is used to improve the performance of the copper powder. • The method integrates passivation, silver-coating, and coupling agent treatment. • The stability of the copper powder has been improved after the modification. • The sheet resistance of the conductive film is reduced to 15 mΩ. -- Abstract: The specific goal of the present study is to evaluate the surface performance of the copper particles and get excellent copper powder by surface modification. This paper proposes a combinative modification method integrating passivation, silver-coated, and coupling agent. As a result, after 600 h at room temperature the copper powder has the stabilization improved and is well combined with organic matters, and the sheet resistance of the film fabricated by the copper conductive filler is reduced to 15 mΩ. The performance of the copper powder has been greatly enhanced by the combinative modification, and the cost of the copper conductive filler is decreased significantly by this method. The results indicate that the combinative surface modification method can be used for practical electronic application

[en] Ba_0.6Sr_0.4TiO₃ (BST) thick films were fabricated on Al₂O₃ substrate via the screen printing technology by using B₂O₃-Li₂O additions as liquid-phase sintering aids. The effects of doping of B₂O₃ and Li₂CO₃ on the phase compositions, microstructures, and dielectric tunable properties of the thick films were investigated systematically. The X-ray diffraction patterns showed that BST diffraction peaks shifted toward higher angle with the B₂O₃-Li₂O doping content, which indicated the substitution of B³⁺ and Li⁺ in Ba²⁺ site. It was also found that the grain size and electrical properties of the thick film were strongly affected by the glass content. The grain size and the relative permittivity decreased obviously with the increase of B₂O₃-Li₂O additive. In addition, for the thick film with 4.5 wt% glass content, optimized sintering, and electrical properties were obtained: the sintering temperature of 900 C, relative permittivity of 312 (at 10 kHz), dielectric loss of 0.0039, tunability of 16.2% (at 3 kV/mm). These good sintering and electrical properties indicate that BST thick film with B₂O₃-Li₂O addition is benefit for the development of LTCC technology and tunable devices. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Anti-ferroelectric (AFE) composite ceramics of (Pb_0_._8_5_8Ba_0_._1La_0_._0_2Y_0_._0_0_8)(Zr_0_._6_5Sn_0_._3Ti_0_._0_5)O_3-(Pb_0_._9_7La_0_._0_2)(Zr_0_._9Sn_0_._0_5 Ti_0_._0_5)O_3 (PBLYZST-PLZST) were fabricated by the conventional solid-state sintering process (CS), the glass-aided sintering (GAS), and the spark plasma sintering (SPS), respectively. The influence of the temperature induced phase transition on the phase structure, hysteresis loops, and energy storage properties of the composite ceramics were investigated in detail. The measured results of X-ray diffraction demonstrate that the composite ceramics exhibit the perovskite phases and small amounts of non-functional pyrochlore phases. Compared with the CS process, the GAS and SPS processes are proven more helpful to suppress the diffusion behaviors between the PBLYZST and PLZST phases according to the field emission scanning electron microscopy, thereby being able to improve the contribution of PBLYZST phase to the temperature stability of the orthogonal AFE phase. When the ambient temperature rises from 25 °C to 125 °C, CS and GAS samples have undergone a phase transition from orthorhombic AFE phase to tetragonal AFE phase, which results in a sharp decline in the energy storage density. However, the phase transition temperature of SPS samples is higher than 125 °C, and the energy storage density only slightly decreases due to the disorder of material microstructure caused by the high temperature. As a result, the SPS composite ceramics obtain a recoverable high energy storage density of 6.46 J/cm"3 and the excellent temperature stability of the energy storage density of 1.16 × 10"−"2 J/°C·cm"3, which is 1.29 × 10"−"2 J/°C·cm"3 lower than that of CS samples and about 0.43 times as that of GAS samples

[en] Highlights: • Eliminating doping effect and redistributing electric field results in decreased permittivity and increased tunability. • WIncreasing MgO content, permittivity of composite films decreases and tunability shows a trend of first rise and then fall. • The tunability of composite film with 30 wt% MgO under 32.5 kV/mm can reach to 25.6%, 1.22 times that of pure P(VDF-TrFE). -- Abstract: Ferroelectric-dielectric composite has the potential to combine low dielectric constant of the dielectrics with the high tunability of ferroelectrics. However, one significant drawback of the composites is that the decreased dielectric constant is at the expense of tunability. Here, we eliminate the doping effect through organic-inorganic compositing and redistribute electric field to let the tunability increases while dielectric constant decreases. Poly(vinylidene fluoride-trifluoroethylene) copolymers based ferroelectric-dielectric composite films were prepared through spinning-coating method and the effect of MgO content on the dielectric tunable properties was studied. With increasing MgO content up to 30 wt%, the tunability of composite films increased while the dielectric constant decreased. The tunability of P(VDF-TrFE)-MgO composite films with 30 wt% MgO at 10 kHz under 32.5 kV/mm can reach to 25.6%, 1.22 times that of pure P(VDF-TrFE) (20.9%). This research paves a new pathway to increase the tunability and decrease the dielectric constant of ferroelectric materials simultaneously.

[en] (Pb_0.87La_0.02Ba_0.1)(Zr_0.7Sn_0.3-x Ti_x)O₃ (PLBZST, 0.06 ≤x ≤0.09) antiferroelectric ceramics were fabricated by conventional solid state reaction process, and their ferroelectric, dielectric, and pyroelectric properties were systemically investigated. PLBZST with different Ti content were all confirmed to be in an antiferroelectric phase at T=50 C, which is close to the lowest phase transition temperature. Compared with conventional FE ceramics, PLBZST antiferroelectric ceramics exhibited higher electric field induced pyroelectric coefficient (p). As the content of Ti increased from 0.06 to 0.09, the pyroelectric coefficient increased from 1000 to 6500 μC/m ²K under a 500 V/mm DC bias field. The maximum pyroelectric coefficient of 8400 μC/m ²K was obtained at x=0.09 when an 850 V/mm DC bias field was applied, which is far larger than that of conventional phase transition pyroelectric materials. Large pyroelectric response is beneficial for the development of infrared detectors and thermal imaging sensors. (orig.)

[en] (Pb_0.87La_0.02Ba_0.1) (Zr_0.7Sn_0.24Ti_0.06)O₃ (PLBZST) antiferroelectric ceramics with the addition of 0-9 wt. % excess PbO were fabricated by the conventional solid-state reaction process, and their microstructure, dielectric, and pyroelectric properties were systemically investigated. When excess PbO content was less than 9 wt. %, two pyrochlore phases were formed along with the perovskite phase. Compared with common specimens, PLBZST antiferroelectric ceramics with excess PbO exhibited a higher pyroelectric coefficient and a lower dielectric loss, which are beneficial for the development of pyroelectric devices. Around the Curie temperature, as the excess PbO increased from 0 wt. % to 9 wt. %, PLBZST ceramics' pyroelectric coefficient increased from 1600 μC/m²K to 4000 μC/m²K, and the figure of merit increased from 40 x 10^-5 Pa^-0.5 to 140 x 10^-5 Pa^-0.5 under a 400 V/mm dc field. The largest figure of merit of 200 x 10^-5 Pa^-0.5, which is about 8 times higher than that of conventional phase transition materials barium strontium titanate (BST), was obtained in PLBZST ceramics with 6 wt. % excess PbO when a 600 V/mm dc bias field was applied. Therefore, improvement of pyroelectric property is beneficial for the development of infrared detectors.

[en] Ba_0.7Sr_0.3TiO₃ (BST) ceramics with different dopants and various grain sizes were fabricated by the solid-state reaction process, and the doping and grain size effects on dielectric and dc bias field-induced pyroelectric properties were systemically investigated. When acceptors were added, the dielectric loss of the BST was decreased effectively, whereas the pyroelectric coefficient was decreased for the broadening of dielectric constant peaks. With the increase of the content of acceptors and the adding of donors simultaneously, the decrease of pyroelectric coefficient caused by the doping effect could be weakened. The dielectric and dc bias field-induced pyroelectric properties were also affected by the grain size effects dramatically. In this paper, the best pyroelectric coefficient of 105 x 10^-8 C/cm² C and figure-of-merit of 22 x 10^-5 Pa^-0.5 could be obtained when the grain size was 1 μm. The systemic investigation of doping and grain size effects would contribute to the development of high pyroelectric properties of BST for uncooled infrared detector. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)