A.H. Salama
材料科学技术（英文）
Li-doped p-type ZnO ceramics were prepared by conventional methods according to the chemical formula Zn1-x LixO2 where x=0.5, 1.0, 1.5 and 2.0 mole fraction, respectively. The crystal structures of the prepared samples were studied by X-ray diffraction analysis. The dielectric properties (including dielectric constant ε'
and dielectric loss ε") and dc-electrical conductivity [σ(Ω-1·cm-1)] were investigated. The dielectric constant ε' was sharply decreased at the low frequency range and independent on frequency at high frequency range. Otherwise, the dielectric loss "00 varied with frequency and showed absorption peak located from 200 Hz to
4 kHz and moved to higher frequency as the concentration of Li+ doped increased. It was found that dc-electrical conductivity log¾ varied from -9 to-5 and the energy gap width were calculated by using Arrhenius equation. The p-type conductivity of Li-doped ZnO may be attributed to the formation of a LiZn-Lii donor complex, which is limited by reducing the amount of Lii.
关键词:
P-type ZnO ceramics
Xiujian Chou
材料科学技术（英文）
Ba1-xSrxTiO3 ceramics, doped with B2O3-Li2O glasses have been fabricated via a traditional ceramic process at a low sintering temperature of 900 °C using liquid-phase sintering aids. The microstructures and dielectric properties of B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have been investigated systematically. The temperature dependence dielectric constant and loss reveals that B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have diffusion phase transformation characteristics. For 5 wt% B2O3-Li2O glasses doped Ba0:55Sr0:45TiO3 composites, the tunability is 15.4% under a dcpplied electric field of 30 kV/cm at 10 kHz; the dielectric loss can be controlled about 0.0025; and the Q value is 286. These composite ceramics sintered at low temperature with suitable dielectric constant, low dielectric loss, relatively high tunability and high Q value are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential microwave tunable devices applications.
关键词:
Sintering
Wenbo FEI
材料科学技术（英文）
This paper shows that it is easier to form intelligent ceramics than other materials. Self-adaptive factors and relevant function mechanisms, which determine the formation of intelligent ceramics, are studied and data from the design of the PLZT with complex functions are presented.
关键词:
Shengyu JIANG
,
Jiancheng ZHANG
,
Feng GU
,
Yue SHEN
,
Hua WANG
材料科学技术（英文）
Glass-ceramics containing β-quartz as a main crystal phase based on the system of SiO2-Al2O3-Li2O-K2O-MgO-ZnO were investigated for the application to magnetic storage substrate for higher storage capacity. Parent glasses were prepared, then nucleated and crystallized at certain temperatures for 3~4 h. The crystallization kinetics of glass-ceramics was also studied. The grain size was estimated by Scherrer formula and image treatment of transmission electron microscopy (TEM). The results π showed that the Avrami exponent was determined to be 3.88, the activation energy 189±7 kJ/mol and the grain size 30~60 nm. A detailed microstructure of the glass-ceramics, including grain distribution and the morphology of nano-crystalline was characterized by TEM, X-ray diffraction (XRD), differential scanning calorimeter (DSC), differential thermal analysis (DTA). The relationship between microstructure and mechanical properties was also discussed.
关键词:
Glass-ceramics
,
动力学
,
磁盘基片
Zhijun LIN
,
Meishuan LI
,
Yanchun ZHOU
,
null
,
null
材料科学技术（英文）
Layered ternary ceramics represent a new class of solids that combine the merits of both metals and ceramics. These unique properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), convergent beam electron diffraction (CBED) represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Microstructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the ``Processing-Structure-Property" relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.
关键词:
Layered ternary ceramics
,
ternary
,
ceramics
,
MAX
,
phase
,
TEM
,
S
Applied Physics Letters
The effect of high-energy ball milling on the structure of nanometer sized amorphous ceramics, a-Si3N4 and a-Si-N-C, respectively, has been investigated. At high milling intensity, a-Si3N4 may rapidly crystallize into a mixture of alpha-Si3N4 and beta-Si3N4 after the initial 4 s of milling whereas no structural changes were observed at low milling intensity. For a-Si-N-C, mechanical milling does not cause structural changes at both low and high intensity. It was found that extension of mechanical milling of these hard ceramics can introduce large volume fractions of contamination fragments from the milling media. We conclude that the observed structural changes occurring in a-Si3N4 may be due to mechanical effect, rather than local heating and/or impurity effect. (C) 1996 American Institute of Physics.
关键词:
ni-zr;alloys;powders;metals
Materials Science and Technology
In order to meet increasing requirement for the evaluation and design of damage tolerance of brittle materials, a simple expression was proposed to estimate the damage tolerance quantitatively using basic material parameters, based on the features of damage tolerance and fracture mechanics. The calculated results from this equation indicated that the damage tolerance of nanolayer grained ceramics was over 10 times higher than that of some brittle ceramics, while glass has the lowest damage tolerance. Therefore, the damage tolerance of various ceramics can be estimated directly using their basic properties data without the necessity of additional tests. SEM examination and finite element simulation showed that the high damage tolerance of the layer grained ceramics was attributed to delamination in grains, interlocking microstructures and crack deflection.
关键词:
damage tolerance;brittle material;nanolayer grained ceramics;reliability;liquid reaction synthesis;ti3sic2;ti3alc2;microstructure;indentations;glass
