Lei Hou

Beijing University of Technology, Peping, Beijing, China

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Publications (9)12.72 Total impact

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    ABSTRACT: One dimensional ferroelectric nanostructure is noteworthy for their size-dependent dielectric, piezoelectric, and electro-optic properties with corresponding applications in smart devices such as transducers, actuators, and high-k dielectrics at the nanoscale. Due to their extremely small size and anisotropy, the control of nucleation and growth of one dimensional nanostructure materials is still a big challenge. Sol–gel-hydrothermal chemistry combines both the merits of sol–gel and hydrothermal technique, which offers a very useful tool for low-temperature synthesis of the ferroelectric nanowires. In this paper, we will review recent works devoted to the synthesis of Bi-based complex perovskite nanowires, i.e. Na0.5Bi0.5TiO3, K0.5Bi0.5TiO3, (K0.5Bi0.5)0.4Ba0.6TiO3 and (Na0.8 K0.2)0.5Bi0.5TiO3 systems. We will focus on the formation mechanism and morphology evolution of nanowires prepared in sol–gel-hydrothermal process. Moreover, due to the good sinterability of the nanowires, the high-densified single-phase ceramic can be fabricated even by a conventional sintering process. KeywordsPerovskites–Grain growth–Sol–gel processes–Calcination–Hydrothermal
    Journal of Electroceramics 01/2011; 26(1):37-43. · 1.42 Impact Factor
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    ABSTRACT: The sol–gel–hydrothermal processing of (Na0.8K0.2)0.5Bi0.5TiO3 (NKBT) nanowires as well as their densification behavior were investigated. The morphology and structure analyses indicated that the sol–gel–hydrothermal route led to the formation of phase-pure perovskite NKBT nanowires with diameters of 50–80 nm and lengths of 1.5–2 μm, and the processing temperature was as low as 160°C, but the conventional sol–gel route tended to lead to the formation of NKBT agglomerated porous structured nanopowders, and the processing temperature was higher than 650°C. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowires at a low temperature. Owing to the better packing efficiency and therefore a good sinterability of the freestanding nanowhiskers, the pressed pellets made by NKBT nanowires showed >98% theoretical density at 1100°C for 2 h. The sol–gel–hydrothermal-derived ceramics have typical characteristics of relaxor ferroelectrics, and the piezoelectric properties were better than the ceramics prepared by the conventional sol–gel and solid-state reaction.
    Journal of the American Ceramic Society 06/2007; 90(6):1738 - 1743. · 2.43 Impact Factor
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    ABSTRACT: A kind of lead-free ferroelectric nanorods, (K0.5Bi0.5)0.4Ba0.6TiO3, has been prepared by the sol–gel process. The phase formation, structure and morphological analyses of (K0.5Bi0.5)0.4Ba0.6TiO3 were investigated by XRD, FTIR, Raman and TEM. The results revealed that single-crystalline (K0.5Bi0.5)0.4Ba0.6TiO3 nanorods with width around 80 to 120 nm, and length around 200–300 nm were obtained by calcining dried gels at 800 °C for 2 h. Raman analysis of (K0.5Bi0.5)0.4Ba0.6TiO3 nanorods indicated that A1(TO2) and E(TO) mode incorporated into one broad peak at around 285 cm− 1, which can be attributed to the cation disorder (Bi, K, Ba) on the 12-fold coordinated A site of ABO3 structure.
    Materials Letters. 06/2007;
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    ABSTRACT: ( K <sub>0.5</sub> Bi <sub>0.5</sub>)<sub>0.4</sub> Ba <sub>0.6</sub> Ti O <sub>3</sub> nanowires have been fabricated by a sol-gel–hydrothermal method at 200 ° C . X-ray diffraction result shows that the nanowires have a tetragonal perovskite structure. Transmission electron microscopy investigations exhibit that the as-prepared nanowires are single crystalline grains with diameters of about 40 nm and lengths reaching up to 800 nm . The ( K <sub>0.5</sub> Bi <sub>0.5</sub>)<sub>0.4</sub> Ba <sub>0.6</sub> Ti O <sub>3</sub> ceramics with a relative density of 97% can be fabricated from the high quality nanowires even by a conventional sintering process, which showed that typical characteristics of relaxor ferroelectrics, the indicator of degree of diffuseness γ and Curie temperature T<sub>C</sub> (100 kHz ) , were 1.65 and 220 ° C , respectively.
    Applied Physics Letters 01/2007; · 3.52 Impact Factor
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    ABSTRACT: A kind of novel lead-free ferroelectrics, potassium bismuth titanate, K0.5Bi0.5TiO3 (KBT), has been prepared by sol–gel-hydrothermal and sol–gel routes, respectively, and the structural characters of as-synthesized powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicated that sol–gel-hydrothermal route led to the formation of KBT nanowhiskers with diameters of 20nm and lengths of 1μm, and the processing temperature was as low as 160°C, but the normal sol–gel route tended to form KBT cubic particles of about 100–200nm, and the processing temperature was higher than 700°C. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowhiskers at low temperature. Due to the good sinterability of nanowhiskers, the ferroelectric and dielectric properties of KBT ceramics prepared by sol–gel-hydrothermal route were super to that prepared by sol–gel route.
    Solid State Communications 01/2006; 137(12):658-661. · 1.53 Impact Factor
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    ABSTRACT: A lead-free ferroelectric material, (K0.5Bi0.5)TiO3 (KBT), was prepared by a sol–gel process. Thermal analysis and X-ray diffraction showed that perovskite KBT powders with a grain size of 100–200nm were obtained by calcining dried gels above 700°C. When the calcining temperature was lower than 650°C, only the Bi2Ti2O7 phase was found in the X-ray diffraction patterns. Moreover, KBT ferroelectric ceramics was fabricated by traditional sintering of as-prepared KBT powders. The KBT ceramics sintered at 1050°C showed a high density (91.2% of theoretic density) and low dielectric loss, better than that prepared by a solid-state reaction method. The temperature dependence of dielectric permittivity of KBT ceramics showed a Curie temperature at 385°C.
    Materials Chemistry and Physics - MATER CHEM PHYS. 01/2006; 99(2):329-332.
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    ABSTRACT: The sol–gel-hydrothermal processing of K0.5Bi0.5TiO3 (KBT) nanowires as well as their sintering behavior at 1000–1100°C were investigated. The morphological analyses indicated that sol–gel-hydrothermal route led to the formation of KBT nanowires with diameters of 4nm and lengths of 100nm at low processing temperature of 200°C with KOH concentration of 6M. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowires. The KBT ceramics with a relative density of more than 95% can be successfully fabricated from the high quality KBT nanowires even by a conventional sintering process. The KBT ceramics sintered at 1050°C showed typical characteristics of relaxor ferroelectrics, and the dielectric properties were better than that prepared by all other methods reported previously.
    Materials Research Bulletin - MATER RES BULL. 01/2006; 41(7):1330-1336.
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    ABSTRACT: ZnTiO3 powders with pure hexagonal phase were prepared by the sol–gel process with Zn(NO3)2·6H2O and Ti(OC4H9)4 materials. The thermal behavior and phase transformation of the gels were investigated by the differential scanning calorimetry–thermogravimetry (DSC–TG) analysis, X-ray diffraction (XRD) patterns, Fourier-transforming infrared (FT-IR) spectroscopy, and Raman scattering spectroscopy. The results revealed that pure hexagonal phase of ZnTiO3 could be obtained at low temperature of 800 °C. However, in further increased temperature above 900 °C, hexagonal ZnTiO3 would decompose into cubic Zn2TiO4 and rutile TiO2.
    Materials Letters 02/2005; 59(2):197-200. · 2.27 Impact Factor
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    ABSTRACT: A kind of novel lead-free ferroelectrics, potassium bismuth titanate, K0.5Bi0.5TiO3 (KBT), has been prepared by the sol–gel process. The amorphous dried gels were first transformed into Bi2Ti2O7 phase at low heat-treated temperature and as the temperature increased to 700°C, only pure KBT phase can be observed and there was no evidence of second phase. KBT ferroelectric ceramics were fabricated from the natural sintering of 700°C-treated powders, which have a particle size of 100–200nm. The KBT ceramics sintered at 1050°C showed typical characteristics of relaxor ferroelectric, and the dielectric properties were better than that prepared by a solid-state reaction method.
    Journal of Crystal Growth 01/2005; 273(3):500-503. · 1.55 Impact Factor