Influence of synthesis temperatures on the crystalline grain growth and morphology of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaaluminate（LaMgAl（11）O（19）, LMA） was prepared at different temperatures by solid-state reaction. Phase compositions and crystal morphologies of specimens synthesized at different temperatures were investigated using X-ray diffraction（XRD）, scanning electron microscopy（SEM）. It was observed that the crystalline grain size of LMA was not only dependent on the preparation temperature but also on its powder morphology. In the temperature range of 1300 e1550℃, LMA showed platelet grain and the average crystalline grain size increases with the increase in temperature. At1600℃, if the powder was sintered for two times, the equiaxed grain could be found with the decrease in grain space, resulting in the reduction of the crystalline grain size. Styles of specimens（powder or disk） might have no obvious influence on morphologies and sizes of LMA crystalline grains which were synthesized with the well-dispersed raw material mixtures. The synthesis temperature played a key role in influencing the free space for the formation and growth of crystalline grains.

Correlation between the Low-Temperature Photoluminescence Spectra and Photovoltaic Properties of Thin Polycrystalline CdTe Films

A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-temperature photoluminescence spectra of fine-grained obliquely deposited films. Doping film with In impurity leads to quenching of the doublet band, while further thermal treatment causes activation of the intrinsic band, the half-width and the blue shift of the red edge of which correlates with the maximum value of anomalously high photovoltage generated by the film.

Effect of Temperature Schedule on the Morphology of SiC Made From Graphite and Silicon Powder

SiC whiskers were synthesized in a coke bed using a two-step heat treatment process.The temperature was held for 3 h at 1 200 ℃ before heating to 1 430 ℃ and holding for 3 h.The morphologies of SiC synthesized by the two-step heat treatment method were much more different from those produced by direct heating to 1 430 ℃.SiC whiskers formed at 1 200 ℃ firstly and grew at1 430 ℃ to obtain a mean diameter about 326 nm,while the SiC grains with a size range from 0.70 to2.30 μm were obtained by direct heating to the target temperature of 1 430 ℃.This was explained by the different formation mechanisms.The result proposes a promising alternative technical process for whisker-reinforced ceramic/refractory composites in-situ during sintering.

Control of growth and structure of Ag films by the driving frequency of magnetron sputtering

The growth and structural properties of Ag films prepared by radio-frequency（2, 13.56 and27.12 MHz） and very-high-frequency（40.68 and 60 MHz） magnetron sputtering were investigated. Using 2 MHz sputtering, the Ag film has a high deposition rate, a uniform and smooth surface and a good fcc structure. Using 13.56 and 27.12 MHz sputtering, the Ag films still have a high deposition rate and a good fcc structure, but a non-uniform and coarse surface.Using 40.68 MHz sputtering, the Ag film has a moderate deposition rate and a good fcc structure, but a less smooth surface. Using 60 MHz sputtering, the Ag film has a uniform and smooth surface, but a low deposition rate and a poor fcc structure. The growth and structural properties of Ag films are related to the ions＇ energy and flux density. Therefore, changing the driving frequency is a good way to control the growth and structure of the Ag films.