Papers by Author: Xiu Li Chen

Abstract: Ba0.6Sr0.4TiO3 nanopowders (~ 80 nm in size) were prepared by low temperature hydrothermal process. The process and synthesis mechanism were discussed in detail. Furthermore, the powders were pressed into disc-shaped pellets and sintered at different temperatures. The frequency dependence of the dielectric constant and loss angle tangent of the sintered BST ceramics are measured from room temperature to 500°C and a diffuse dielectric anomaly by the dielectric relaxation was found.

Abstract: Lead magnesium niobate-lead titanate (0.8Pb(Mg1/3Nb2/3)O3-0.2PbTiO3, PMN-PT) thick films in the thickness range about 75 μm have been successfully fabricated on Au-coated Al2O3 substrates by electrophoretic deposition (EPD). Non-aqueous colloidal suspensions suitable for EPD were prepared by mixing ultrasonically PMN-PT particles in ethanol with pH=6.0. The effect of EPD process parameters such as deposition voltage, deposition time and the specific deposition mass of PMN-PT particles were investigated. The EPD parameters were optimized in order to obtain crack-free, high-quality uniform ceramic films. The deposited pyrochlore-free PMN-PT thick films were sintered at 1000oC for 30 min, and the phase evolvement and the microstructure of the film were characterized by X-ray diffraction and scanning electron microscope.

Abstract: A relaxor ferroelectric material, Pb(Mg1/3Nb2/3)O3 (PMN) powder with a pyrochlore-free phase, was prepared by using a one-step calcinations method. The pyrochlore phase was prevented by coating Mg(OH)2 on Nb2O5 particles. Pure-perovskite PMN powder was synthesized by a single calcination of the coating powder mixed with appropriate amounts of PbO at 900 oC for 2 h. The pyrochlore-free perovskite PMN powders were sintered to 96.9% density at 1100 oC. The sintered PMN ceramics exhibited a dielectric constant maximum of ~11 700 at room temperature at a frequency of 1 kHz.

Abstract: Relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) crystals were grown at low temperature by a single-step hydrothermal process, using the mixture of PbO, MgO and Nb2O5 as precursors. The precursors were just heated to 150 oC for 24 h. The effect of the KOH concentration on the morphology and microstructure of PMN crystals was systematically investigated. The optimum KOH concentration was found to be 11M, which led to the stabilization of the perovskite crystals against the pyrochlore phase, and to the growth of high-quality PMN crystals suitable for subsequent characterization. According to morphological evolution during the reaction, two possible growth mechanisms are proposed. When the KOH concentration is 11M, at the early stage of the reaction, the starting materials dissolve, and then promote the formation of spherical intermediate pyrochlore phase followed by the formation of primary cubic PMN crystals. At the same time, a platelet-shaped intermediate pyrochlore phase also forms and then grows into larger platelet-shaped PMN crystals.

Abstract: Barium modified lead zirconate titanate (PBZT) thin films were grown epitaxially on Pt/Ti/SiO2/Si substrates by radio-frequency magnetron sputtering deposition and characterized by X-ray diffraction and scanning electron microscopy. Depending on the growth condition, a wide variation of crystal structure and morphology was evolved in PBZT thin films. The formation of phase structure and pyrochlore phase was strongly dependent on the oxygen partial pressure and re-evaporation of lead from the films during the deposition. Perovskite films were obtained by optimizing the deposition conditions and analyzed by the ferroelectric hysteresis (P~E).

Abstract: Relaxor-based lead-lanthanum-zirconate-titanate (PLZT) thick films were prepared on Ti substrates by a simplified hydrothermal method, in which the precursors were heated to 150 oC with durations from 8 to 32h. The mixture of oxides was used as the staring materials. The smooth PLZT films with a single perovskite structure were obtained through the synthesis route. Structural and morphological studies were carried out on hydrothermally synthesized films. The influences of the mineralizer concentration on the structural, morphological, and physical characteristics of the particles are studied. Phase characterization and crystal orientation of the PLZT thick films were investigated by x-ray diffraction analysis (XRD). The dielectric constant and dielectric loss of the PLZT thick films were measured. In the frequency range from 1000 to 100 MHz, the dielectric constant and the dielectric loss were very steady.