Yudong Xu

Effect of nano-micro TiN addition on the microstructure and mechanical properties of TiC based cermets

In this paper the titanium carbide based cermets with addition of nano-micro titanium nitride were fabricated by conventional powder metallurgy techniques. The microstructure of TiC based cermets with nano-micro TiN addition has been investigated by transmission electron microscope (TEM) and a scanning electron microscope (SEM). Bending strength, fracture toughness and hardness were also measured. Results reveal that mechanical properties do not change monotonously with increasing nano TiN addition. Results also show that nano titanium nitride addition can prevent the coalescence of TiC grains. It is also found that nano TiN is distributed at the interface of TiC/TiC grains and that the growth of TiC grains is impeded by the presence of nano TiN particles and that the result is an increase in mechanical properties.

Giant electrostrictive effects of NaNbO3-BaTiO3 lead-free relaxor ferroelectrics

A giant electrostrictive effect was observed in (1 − x)NaNbO3-xBaTiO3 relaxor ferroelectric ceramics, which exhibit a high electrostrictive coefficient Q33 of ∼0.046 m4/C2 twice as large as those of Pb- and Bi-based perovskite relaxor ferroelectric ceramics. The theoretical analysis suggests that Q33 should be strongly correlated with chemical species of cations in a perovskite structure in which a strong ionic bond is of great benefit compared with a covalent bond. A hysteresis-free large electrostrictive strain of ∼0.148% up to at least 70 Hz was obtained in the x = 0.25 sample, demonstrating significant advantages over piezoelectric effects in high-precision ceramic actuators.

SYNTHESIS OF STRONTIUM-AND MAGNESIUM-DOPED LANTHANUM GALLATE BY GLYCINE-NITRATE COMBUSTION METHOD

Sr- and Mg-doped lanthanum gallate powders with the composition of La0.85Sr0.15Ga0.85Mg0.15O2.85 were synthesized by a glycine-nitrate combustion method. Powders prepared under different fuel combustion conditions were investigated by XRD and TEM. The results show that, under slightly rich fuel condition, the product powders contain less impurity phases, and powders prepared by the glycine-nitrate combustion contain far less impurity phases and have smaller particle sizes than those prepared by solid-state reaction method or acrylamide polymerization technique.

Red emission enhancement for CaAl12O19:Cr3+ and CaAl12O19:Mn4+ phosphors

In order to enhance the deep red emission intensities of CaAl12O19:Cr3+ and CaAl12O19:Mn4+ phosphors, the authors prepared a series of samples through doping a variety of ions with different valence states at 1500 °C by solid state reaction in air. Their doping effects and possible mechanisms were investigated, respectively. The results indicated that Sm3+ could enhance the emission intensity of CaAl12O19:Cr3+ through an energy transfer process, whereas it has not a similar effect for the CaAl12O19:Mn4+ phosphor. It is also shown that Cl−, Mg2+ and K+ could enhance the emission intensity of CaAl12O19:Mn4+ mainly due to their charge compensation effects. What is more interesting is that the doped Ge4+ ion, as a type of covalent ion of Mn4+, also has the ability to enhance the red emission intensity of CaAl12O19:Mn4+ through decreasing the concentration of Mn4+–Mn4+ pairs in the prepared phosphor.

Magnetostatic Coupling in CoFe2O4/Pb(Zr0.53Ti0.47)O3 Magnetoelectric Composite Thin Films of 2-2 Type Structure

CoFe2O4/Pb(Zr0.53Ti0.47)O3 (CFO/PZT) magnetoelectric composite thin films of 2-2 type structure had been prepared onto Pt/Ti/SiO2/Si substrate by a sol-gel process and spin coating technique. The structure of the prepared thin film is substrate/PZT/CFO/PZT/CFO. Two CFO ferromagnetic layers are separated from each other by a thin PZT layer. The upper CFO layer is magnetostatically coupled with the lower CFO layer. Subsequent scanning electron microscopy (SEM) investigations show that the prepared thin films exhibit good morphologies and compact structure, and cross-sectional micrographs clearly display a multilayered nanostructure of multilayered thin films. The composite thin films exhibit both good magnetic and ferroelectric properties. The spacing between ferromagnetic layers can be varied by adjusting the thickness of intermediate PZT layer. It is found that the strength of magnetostatic coupling has a great impact on magnetoelectric properties of composite thin films, i.e., the magnetoelectric voltage coefficient of composite thin film tends to increase with the decreasing of pacing between two neighboring CFO ferromagnetic layers as a result of magnetostatic coupling effect.