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Grain Growth Kinetics and Debye Temperature of Nanometer TiO_2 Powders Prepared by a Sol-gel Process

Ju LUO , Xingzhao DING , Benpei CHEN and Jie KONG(Institute of Solid State Physics , Academia Sinica , Hefei , 230031 , China)Yuanda DONG(Dept. of Metallurgy and Materials , Shanghai University of Technology , Shanghai , 200072 , China)

材料科学技术（英）

The development of microstructure of nanometer TiO2 powders prepared by a sol-gel process was systematically studied. Grain growth was mon itored using X-ray diffraction (XRD) and transmission electron microscopy (TEM). and the Debye temperature of anatase crystallites was determined. It was found that the grain size of the powders increased slowly with annealing temperature up to 773 K. but grew rapidly in the temperature range of 773-1273K. The activation energies (Ea) for the growth of anatase crystallites in the two temperature regions were calculated to be 16 and 90 kJ / mol, respectively. The Debye temperatures of nanocrystalline anatase powders were all lower than that of microcrystalline anatase. which implies that the bonding force between Ti and O atoms in nanocrystalline TiO2 shourd be smaller than that in microcrystalline state. However. it was noted that the Debye temperature of nanocrystalline anatase increased with the decrease of grain size. This may be attributed to the enhancement in atomic bonding force due to the existence of high surface tension in nanocrystalline powders

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Mossbauer Spectroscopic Studies on a Supersaturated Solid Solution of Fe-Cu Formed by Mechanical Alloying

Yuanzheng YANG and Xueming MA (Institute of Solid State Physics , Academia Sinica , Hefei , 230031 , China)(To whom correspondence should be addressed)Yuanda DONG(Dept. of Metallurgy arid Materials , Shanghai University of Technology , Shanghai , 200072 , China)

材料科学技术（英）

Mechanical alloying (MA) was employed to produce supersaturated solid solutions of Fe1-xCux,which is virtually immiscible under an equilibrium condition at ambjent temperature. The X-ray diffraction results show that the solutions formed in the concentration ranges of x≤0.1 5 and x≥0.40 are of bcc structure of iron and fcc structure of copper. respectively. For the region in between.however, the alloy obtained is a mixture of bcc plus fcc phases. The Mossbauer spectrum of the solid solution of a single phase could be fitted by two sub-spectra with hyperfine magnetic fields of 200 and 250 kOe. respectively. suggesting that there must exist two forms of coordination in the solution. While to fit the spectrum for the solution with mixed structu re. three Sub-spectra. including a spectrum of α-Fe, should be used. The variation of the Mossbauer spectra of Fe60Cu40 with milling time as well as annealing temperature was systematically studied. This may be ascribed to the changes of the number of nearest neighboring atoms of iron in the processes of formation and decomposition of the solid solution during milling and annealing

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Structural Characteristics of Rapidly Quenched Al-Si Alloys

Lin LIU(Institute of Solid State Physics , Academia Sinica , Hefei , 230031 , China)Yuanda DONG(Dept. of Metallurgy and Materials , Shanghai University of Technology , Shanghai , 200072 , China)

材料科学技术（英）

The structure of rapldly quenched Al-Si alloys (1 and 4 wt-%Si) was systematically studied by optical and transmission electron microscopy (TEM ) as welI as X-ray djffractjon (XRD). ExperimentaIresults show that rapid solidification refines the grain size. extends the solid solubility of Si in Al and Introduces a high density ot defects which exist in the forms of vacancies, dislocations and dislocation loops. etc.. The decomposition process of the alloys was fol lowed by using differential scanning calorimeter (DSC) and the activation energy for precipitation of Si was obtained through Kissinger analysis. The precipitation behaviour of Supersaturated Si in both samples was further examined by TEM. It was found that Si mainly precipitated inside the grains in Al-1 wt-%Si alloy. while in Al-4 wt-%Si alloy. nearly all the Si precipitates distributed along the grain boundaries. This may be due to the structure difference between the alloys in as-quenched state

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Crystal Structure during Film Formation

Guoping DU , Hui SHEN , Lanping YUE , Weiguo YAO , Zongquan LI and Zhenzhong QI (Institute of Solid State Physics , Academia Sinica , Hefei , 230031 , China)(To whom correspondence should be addressed)

材料科学技术（英）

For evaporation-deposited Ti films, face-centred cubic structure was observed at the initial stage of film growth, then transited to the hexagonal close-packed structure during film growing (less than 50 nm thick). While. for ion-beam sputter-deposited films. the structure of films always kept the fcc structure during all stages of film formation. The structure of film at initial growth stages relates with the substrate. It is discussed that different film processes and different growth stages provide different thermodynamic condition of film formation and result in the different crystal structures of films during the film formation

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Investigation on the Initial Stage of Film Growth in Situ

Zhenzhong QI , Guopin DU , Hanqi KE and Weiguo YAO(Institute of Solid State Physics , Chinese Academy of Sciences , Hefei , 230031 , China)

材料科学技术（英）

The initial stage of Ag film growth on Cu(100). Ta(100) and Ta(110) single crystals as well as YBaCuO on Si single crystal covered by Pd was investigated in situ by means of LAS 600 surface analysis system with a sputtering source in sample preparation chamber. The results show that the initial state for Ag / Cu(100) film growth is typical S-K model, for Ag / Ta(100) and Ag / Ta(110)they have the same S-K characteristics, but due to the different surface energies of two crystalline planes. there is some difference for Ag / Ta (100) and Ag / Ta(110). YBCO sputterjng process is rather complex and Cu is the first element appearing in the film.

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