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Low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb(Zr0.49Ti0.51)O3 with LiF and Sm2O3 additives were fabricated by a conventional solid-state reaction. In view of the possible defects caused by LiF doping, the as-sintered specimens were annealed in oxygen to enhance grain size and piezoelectric properties. X-ray diffraction revealed that Sm2O3 and LiF were dissolved in the lattices, forming a pure perovskite structure. Scanning electron microscopy showed that the grain size decreased with increased LiF amount. Hysteresis-loop studies indicated that increased LiF led to ferroelectricity deterioration. Impedance spectroscopy and activation-energy analyses revealed decreased oxygen vacancies after annealing in oxygen. Energy-dispersive spectrometry revealed that fluorine volatilized during annealing in oxygen. Thus, the decreased amounts of FO and VO were presumed responsible for the improved piezoelectric properties. Upon doping 1 mol% LiF, sintering temperature decreased from 1125 to 950 °C. Annealing in oxygen greatly improved the piezoelectric properties from d33 = 252 pC/N and Kp = 0.53 to d33 = 403 pC/N and Kp = 0.56, respectively. [ABSTRACT FROM AUTHOR]

The Ni nanoparticles coated with Pb(Zr,Ti)O (PZT) were synthesized by a sol-gel method and in situ reaction. And their structure, oxidation resistance, and electromagnetic properties were investigated. The X-ray diffraction patterns (XRD) exhibited that a small amount of impure phase characterized to Ni(OH) was detected from the ammonia-treated Ni nanoparticles and the ammonia-treated Ni nanoparticles coated with PZT. After being pre-treated with aqueous ammonia, the PZT coating layer was more uniform and about 10 nm in thickness. The oxidation resistance of the ammonia-treated Ni nanoparticles coated with PZT, compared with that of the non-treated ones, was improved by about 66 °C. The PZT shell layer prepared by in-situ reaction can greatly reduce the dielectric constant and improve the natural resonance loss at high frequency, so as to obtain the optimal impedance matching performance of the electromagnetic wave transmission. [ABSTRACT FROM AUTHOR]

Ba(CeSm)TiAlO (BCSTA, z = 0, 0.25, 0.50, 0.75, 1.00) ceramics sintered in nitrogen atmosphere were prepared by the conventional solid state reaction. The effects of Al substitution for Ti on microstructure and microwave dielectric properties in BCSTA ceramics have been investigated. X-ray diffraction spectra revealed only a single tungsten bronze in all the samples from z = 0 to z = 1.00 and backscatter electronic images confirmed a second BaAlTiO phase at z > 0.50. Besides, XPS results indicated that the incorporation of Al suppressed the reduction of Ti, which leaded to the microwave dielectric properties such as Q × f and τ value improvement in BCSTA ceramics. Typically, the optimum combination of microwave dielectric properties: Q × f ∼ 8401.76 GHz, ε ∼ 71.68, and τ ∼ +4.37 ppm/°C were obtained at z = 0.50 in BCSTA ceramics sintered in nitrogen atmosphere. [ABSTRACT FROM AUTHOR]

The phase structure, ions valence state and microwave dielectric properties of Ba(CeSm)TiO (0 ≤ x ≤ 0.9, BCST) ceramics sintered in air and nitrogen have been investigated. BCST ( x ≤ 0.1) ceramics sintered in air only exhibited peaks associated with tungsten bronze phase structure. A secondary CeO phase appeared for x = 0.5, while CeO and BaTiO phases coexisted for the ceramics with x = 0.9. In contrast, ceramics fired in nitrogen exhibited tungsten bronze phase structure for all compositions from x = 0 to 0.9 within the solid solution. The chemical structure analysis exhibited that, all the sample possessed mixed ion valance states of Ce/Ce and Ti/Ti cations upon oxygen vacancy formations. It is found that incorporation of cerium could significant improve the Q × f values of BCST ceramics sintered in nitrogen with good microwave dielectric properties ( Q × f ∼7536 GHz, ε ∼78, and τ ∼24.61 ppm/°C) at x = 0.5. [ABSTRACT FROM AUTHOR]

Low-temperature sintered LiTiO-based ceramics for low temperature co-fired ceramic resonators were synthesized by a solid state reaction method. Their microwave dielectric properties were further improved by CeO addition. When the amount of CeO increased, the relative permittivity ( ε) of the samples increased a little and then decreased. The quality factor ( Q × f) of the samples was improved obviously for a higher standard reduction potential of cerium than that of titanium. The temperature coefficient of resonant frequency ( τ) of the samples decreased with the increase of CeO addition. CeO mainly existed as a secondary phase and it facilitated the sintering of the LiTiO-based ceramics. Typical microwave dielectric properties of ε = 22.97, Q × f = 34,881 GHz, and τ = 33.12 ppm/°C were obtained for LiTiO + 2 wt% ZnO-BO frit + 0.9 wt% CeO ceramics sintered at 920 °C for 4 h. The addition of oxidizers was proved a promising route to improve the microwave dielectric properties of titanate ceramics sintered at low temperatures. [ABSTRACT FROM AUTHOR]

The aqueous gelcasting-assisted solid-state method (AGAS) and traditional solid-state reaction method (TSSR) were used to prepare Ba[(CoZn)Nb]O (BCZN)-based ceramics. The effects of different powder-preparation methods on the microstructures and dielectric properties of the BCZN-based ceramics were investigated. X-ray diffraction analysis showed completely the same phase compositions regardless of the preparation method adopted. The relative permittivity ( ε) did not significantly vary between the two methods. However, BCZN with CeO-added ceramics prepared by AGAS had higher and more uniform density (6.374 g/cm) and high quality factor of resonant frequency ( Q × f) value (75,843 GHz) than those prepared by TSSR because of the more uniform microstructures, as shown by scanning electron microscopy images. The temperature coefficients of resonant frequency ( τ = 7.4 ppm/°C) of the ceramics prepared by AGAS were also closer to zero than those prepared by TSSR. [ABSTRACT FROM AUTHOR]

The microstructures and electrical properties of Bi0.5(Na1− x− yK xLi y)0.5TiO3 lead-free piezoelectric ceramics were studied. These ceramics were prepared by conventional ceramic technique. XRD analysis reveals that the ceramics possess almost pure perovskite phase when y⩽0.2. The SEM results show that, with more amounts of Li+, the crystalline grain growing speed is accelerated, and the sintering temperature can effectively be decreased. The measurements of piezoelectric properties indicate that the ceramics with relatively low amount of Li+ and high amount of K+ have comparatively large piezoelectricity. The dielectric measurements show that the ceramics have properties like relaxor ferroelectrics and diffuse phase transition (DPT) at Td and Tc, respectively. The results of ferroelectric measurements reveal the system has relatively higher remanent polarization Pr (27.6 μC/cm2) and lower coercive field Ec (37.5 kV/cm). [ABSTRACT FROM AUTHOR]

We describe a new method of fabricating a brush-like polystyrene layer anchored on the surface of the silicon substrate, which involves three steps, namely (i) the attachment of 3-methacryloxypropyltrimethoxysilane onto the silicon surface; (ii) the reaction of vinyl moiety at another extremity of the anchored 3-methacryloxypropyltrimethoxysilane to 4-Hydroxyl-2, 2, 6, 6-tetramethyl-1-piperidinyloxy (HTEMPO·) catalyzed by azobisisobutyronitrile (AIBN); (iii) living free radical grafting polymerization of styrene in the presence of HTEMPO·. The controllable living free radical polymerization permits accurate control of both the molecular weight and the polydispersity. X-photoelectron spectroscopy measurement proved that the alkoxyamine initiator layer forms on the silicon surface. XPS and Ellipsometry measurements showed that the polystyrene chains were covalently anchored onto the silicon surface. The thickness of the grafted polymer layer can be accurately manipulated by altering the polymerization time. The new method allows synthesizing random copolymer and block copolymers by the sequential growth of monomers from the substrate surface. [ABSTRACT FROM AUTHOR]

The influences of pre-firing process and sintering temperature on the microstructure and electrical properties of ZnO-Bi2O3-TiO2-Sb2O3-MnO2-CoO low-voltage varistor ceramics were studied. Especially, twin boundaries and exaggerated grain growth (EGG) were observed here, and the mechanism of EGG was discussed. It seems that the formation of twin boundaries has a correlation with Sb2O3 content and sintering temperature, and that twin boundaries have a great influence in grain growth of ZnO. [ABSTRACT FROM AUTHOR]