Bo Ping Zhang

SPS Sintering of NaNbO3-KNbO3 Piezoelectric Ceramics

Lead-free piezoelectric ceramics have received more attention due to the environmental protection of the earth. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, Spark Plasma Sintering (SPS) was applied to the sintering of Na0.5K0.5NbO3 ceramics, whose powder was synthesized by the conventional oxide mixing method. No loss of sodium and potassium were found in the SPS sintering process, by which the density of the K0.5Na0.5NbO3 solid solution ceramics was raised to 4.21g/cm3 (>93% of the theoretical density) at temperatures as low as 920°C. The crystal phase of the Na0.5K0.5NbO3 is an orthorhombic structure. The piezoelectric parameter (d33) of the K0.5Na0.5NbO3 ceramics reached 49 pC/N.

Chemical Solution Deposition Process and Characterization of Li and Ti Doped NiO Thin Films

Lithium and titanium co-doped NiO ceramics have been found to exhibit a giant low-frequency dielectric constant (ε～105), however, the same system thin films is not yet study. In the present study, Lithium and titanium co-doped NiO thin films were prepared by a chemical solution deposition method using 2-methoxyethanol as a solvent, nickel actate tetrahydrate, lithium acetate dihydrate and titanium isopropoxide as starting materials. The complex oxides such as NiO, Ni0.2O0.8 and NiTiO3 were formed for the Ni0.98Ti0.02O and Ni0.686Li0.294Ti0.02O thin films, and the addition of the lithium lead to the formation of Li2NiO2.888. The dielectric constant of Lithium and titanium co-doped Ni0.686Li0.294Ti0.02O thin films is about 426 at 100 Hz and much higher than that of the titanium-doped Ni0.98Ti0.02O.

Firing and Contact Resistivity of Ag2O-Aided Pb-Free Silver Paste for Crystalline Silicon Solar Cells

The silver pastes containing Ag2O powder, Ag powder, α-terpineol, ethyl-cellulose and Pb-free glass were synthesized for crystalline silicon (c-Si) solar cells. It was found that α-terpineol assisted the decomposition of Ag2O powder and effectively lowered the decomposition temperature of Ag2O. Ag nanoparticles were produced during the decomposition of Ag2O, which helped to reduce the sintering temperature of the silver pastes. The Ag2O-aided silver pastes were fired on polycrystalline silicon solar cells at various temperatures, and large plate-shaped Ag crystallites appeared at the interfaces between the sintered pastes and the emitter, which ensured a good electrical contact. The contact resistivity of Ag2O-aided silver paste with an optimal ratio of Ag2O to Ag was lower than that of the paste with pure Ag powder. The lowest contact resistivity of Ag2O-aided Pb-free silver pastes sintered at 800°C was 0.029 Ω⋅cm2, which was close to that of commercial silver paste that contained Pb-based glass (0.026 Ω⋅cm2). The experimental data demonstrated that the addition of Ag2O reduced the contact resistance and promoted the sintering of Pb-free silver pastes, and Ag2O-aided Pb-free silver paste could be a promising candidate used for front-contact electrode of c-Si solar cells.

Electrical and Physical Properties of Al and Nb Doped PbTiO3 Ceramic Thin Films

A series of Pb(Ti1-xAlx)O3, Pb(Ti1-xNbx)O3 and Pb(Ti1-xAlx/2Nbx/2)O3 thin films were fabricated onto Pt/Ti/SiO2/Si(100) substrates using a chemical solution deposition process. The dielectric constant of the Pb(Ti1-xAlx)O3 thin films increased with increase of aluminum content, while a maximum dielectric constant value was observed for the Pb(Ti1-xNbx)O3 and Pb(Ti1 xAlx/2Nbx/2)O3 thin films when the doping contents were 10 and 20 mol%, respectively. The dielectric constant of the Pb(Ti0.8Al0.1Nb0.1)O3 thin film is about 600, being two times higher than those of Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The Pb(Ti0.8Al0.1Nb0.1)O3 thin film showed less than 10-7 A/cm2 current density at ±150 kV/cm, being superior to the leakage property of the PbTiO3, Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The co-doping of aluminum and niobium is more effective to increase the dielectric and ferroelectric properties as compared with the individual aluminum or niobium doping.

Sb5+ Modified Phase Transition in (Li, Na, K)(Nb1-xSbx)O3 Piezoelectric Ceramics

The modified behavior of the phase transition temperatures (TO-T and/or TC) between orthorhombic (O), tetragonal (T) and cubic (C) that caused by doping Sb5+ in (Li0.052Na0.493K0.455)(Nb1-xSbx)O3 (LNKNSx) ceramics was reported in the present investigation. The results show that differing from the insensitive TO-T to the Sb5+ content, TC splits into two peaks TCI and TCII when doping Sb5+. The decreased TCI by raising x may be ascribed to the Sb-rich grains and the settled TCII round 480 °C resulting from the Sb-lack ones. The enhanced piezoelectric coefficient d33 value of 263 pC/N and planar mode electromechanical coupling coefficient kp value of 42.5% at x=0.052 can be attributed to the polymorphic phase boundary (PPB) behavior with an appropriate ratio between T and O phases without any second phase.

Plasma Sputtering and Optical Properties of Au/SiO2 Nano-Composite Films

Au/SiO2 nano-composite thin films with 3 to 65 vol% Au content were prepared by induction-coil-coupled plasma sputtering. Au particles dispersed in the SiO2 matrix can be prepared by controlling the deposition time of one Au layer and the thickness of the one SiO2 layer. The Au nano-particle dispersed Au/SiO2 multilayer with an uniform nano-layered microstructure showed the absorption peak at the wavelength of 560 nm. The heat-treated Au/SiO2 films containing 3 to 65 vol% Au showed absorption peaks at the wavelength of 540 to 560 nm, while no absorption peak was observed in the as-deposited multilayers containing more than 12 vol% Au.