Narrow Results

The dependencies of the melting point and the lattice parameter of supported metal nanoclusters as functions of clusters height are theoretically investigated in the framework of the uniform approach. The vacancy mechanism describing the melting point and the lattice parameter shifts in nanoclusters with decrease in their sizes is proposed. It is shown that under the high vacuum conditions (p < 10^-7torr) the essential role in clusters melting point and lattice parameter shifts is played by van der Waals forces of cluster–substrate interaction. The proposed model satisfactorily accounts for the experimental data.

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃) or BST thin films on quartz substrates have been prepared by using a modified sol-gel processing technique. The starting materials are barium 2-ethylhexanoate Ba[CH₃(CH₂)₃CH(C₂H₅)CO₂]₂, strontium 2-ethylhexanoate Sr[CH₃(CH₂)₃CH(C₂H₅)CO₂]₂ and titanium (IV) isopropoxide Ti[CH₃CH₃CHO]₄. The precursors Ti[CH₃CH₃CHO]₄ except were synthesized in the laboratory. Transparent and crack-free films were fabricated on quartz substrates by spin coating. The as-fired films were found to be amorphous, which crystallized to cubic phase after annealing at 550°C in air for 1 hr. In this paper, we report the structural and optical properties of BST thin films prepared by the modified sol-gel process.

Fe-based alloy of the composition, Fe₇₄Cu_0.8 Nb_2.7Si_15.5B₇ has been studied thoroughly in order to research the evolution of nanograins and soft magnetic properties. The composition has been significantly deviated from FINEMET type composition given by Fe_73.5Cu₁ Nb₃Si_13.5B₉. It is hard to optimize composition to obtain equally good soft magnetic properties as FINEMET significantly deviating from conventional type alloy. Fe-based alloy of the composition, Fe₇₄Cu_0.8Nb_2.7Si_15.5B₇ has been prepared by single roller melt spinning machine. X-ray diffraction studies confirmed that the ribbon is in the amorphous state. Evolution of α-Fe(Si) nanograins from amorphous matrix were carried out by isothermal annealing in the temperature range from 550°C to 650°C for 1, 3, 5, 10, 20, 30, 40, 50 and 60 minutes. Frequency spectrum of real and imaginary part of complex initial permeability has been measured for the samples at different annealing conditions. Short time annealing has been proved to be more efficient than long time annealing for the samples of this composition for most of the annealing temperatures.

Porous silicon layers have been prepared from n-type silicon wafers of (100) orientation. SEM, XRD, FTIR, and PL have been used to characterize the morphological and optical properties of porous silicon. The influence of varying HF concentration in the anodizing solution, on structural and optical properties of porous silicon has been investigated. It is observed that pore size increases with HF:ethanol concentration ratio and attain maximum for 1:2 ratio and then decreases.

The depth profiles of residual stresses and lattice parameters in the surface layers of shot peened duplex stainless steel at elevated temperature were investigated utilizing X-ray diffraction analysis. At each deformation depth, residual stress distributions in both ferrite and austenite were studied by X-ray diffraction stress analysis which is performed on the basis of the sin${}^2\psi$ method and the lattice parameters were explored by Rietveld method. The results reveal that difference changes of depth residual compressive stress profiles between ferrite and austenite under the same annealing condition are resulted from the diverse coefficient of thermal expansion, dislocation density, etc. for different phases in duplex stainless steel. The relaxations of depth residual stresses in austenite are more obvious than those in ferrite. The lattice parameters decrease in the surface layer with the extending of annealing time, however, they increase along the depth after annealing for 16min. The change of the depth lattice parameters can be ascribed to both thermal expansion and the relaxation of residual stress. The different changes of microstructure at elevated temperature between ferrite and austenite are discussed.

Brass has been tested for the modification in its structural, electrical properties as well as hardness using Au-ion implantation. Four ion doses were devised as follows: $6.74\times 10^{13}$, $1.35\times 10^{14}$, $2.01\times 10^{14}$ and $2.71\times 10^{14}$ ions/cm². SRIM/TRIM software helped to predict Au-ion distribution inside the brass. The alloy was then characterized using X-ray diffraction (XRD), microhardness, four-point probe testing and scanning electron microscopy (SEM) analysis. The microstructure parameters from XRD analysis were determined and used for the calculation of lattice parameter, crystallite size, microstrain and dislocation density. The microhardness value was observed to be changed from 106HV to 119HV with the maximum increase as 12.26%. A noticeable decrease occurred in the crystallite size from 44nm to 34nm for the plane (2 2 0) due to increase in dislocation density, and the corresponding change in ($I$/$I_{\mathrm{\text{max}}})$ is also noted. The electrical conductivity is overall found to be decreased, whereas the $d$-spacing values fluctuated with ion dose. SEM analysis helped observing the microstructural changes, which occurred in the form of particulates and defects, namely pores, voids, cavities and craters. The relationships between microstructure and these properties are important for developing new materials for future prospects.

Extensive progress in brass alloys has been done in surface properties and microstructure. Ti-ion implantation is studied for its effects on electrical resistivity, hardness and microstructure by using scanning electron microscopy, X-ray diffractometer, four-point probe apparatus and Vickers microhardness tester. Ion distribution profile and stopping powers were calculated by Stopping and Range of Ions in Matter (SRIM) code. Nonuniformity in shape, and agglomeration of defects were observed at the surface in SEM micrographs. XRD analysis of (2 0 0) plane for crystallite size, strain, stress and dislocation density is also done. The peak intensity of (2 0 0) is found to be increased by increasing the ion fluence and tensile stresses were also found generated. Increase in the lattice parameter values from 3.681 Å to 3.686 Å appeared as a change in crystallite size, which, in turn, caused an increase in hardness. An increment in electrical resistivity from 7.9$\mu \mathrm{\Omega }$ to 18$\mu \mathrm{\Omega }$ (127.85%) is also observed. For a maximum ion fluence of $2.4\times 10^{14}$ ions/cm², the surface turned out to be amorphous, which helped in making the brass more reliable in its practical usage.

Bright and thick molybdenum (Mo) coatings with good purity and adhesion were electrodeposited on Copper (Cu)-supported Mo/Cu, which is based on aqueous bath containing molybdate ions. All the electrodeposition process was carried out at a fixed duration of 1200s, according to five different current densities 400, 450, 500, 550, and 600mA/cm² at room temperature $25\pm 1^{\circ }$C. Metallic Mo deposits structure may correspond to that of body-centered cubic (bcc) structure. The lattice parameter, residual stress, crystallites size, micro-strain, and dislocation densities were inferred from Mo (110) texture. Synthetized Mo coatings have relatively same rough surface morphology (50–60nm) characterized by some superficial cracks, small uniform grain size having change less than 14%, low residual stress and a good adhesion, a good conductivity, and an appropriate purity that has reached 94 (Mo %wt.). We have deduced that structural and electrical properties of Mo deposits did not obey the existing cracks at surfaces. One important result was that the most cracked and unstressed coating obtained at 450mA/cm² was the same coating having the best purity (Mo %wt.), the best conductivity, and highest free electrons mobility. We suggest that appearance of cracks is closely related to electrochemical facts such as the deposition rate and hydrogen evolution reaction process since cracks decrease beyond 450mA/cm². A good correlation between each investigated property was, also, established and discussed.

Since the lithium-ion conductor Li${}_{10}$GeP₂S${}_{12}$ (LGPS) with a super high room-temperature conductivity of 12mS/cm was first reported in 2011, sulfide-type solid electrolytes have been paid much attention. It was suggested by Kwon et al. [J. Mater. Chem. A3, 438 (2015)] that some excess lithium ions in LGPS, namely, Li${}_{10+\delta }$Ge${}_{1+\delta }$ P${}_{2-\delta }$S${}_{12}$, could further improve their ionic conductivities, and the highest conductivity of 14.2mS/cm was obtained at $\delta =0.35$ though a larger lattice parameter that occurred at $\delta =0.5$. In this study, we focus on these two different chemical compositions of LGPS with $\delta =0.35$ and $\delta =0.5$, respectively. Both samples were prepared using the same experimental process. Their lattice parameter, microstructure and room-temperature ionic conductivity were compared in detail. The results show that the main phase is the tetragonal LGPS phase but with a nearly identical amount of orthorhombic LGPS phase coexisting in both samples. Bigger lattice parameters, larger grain sizes and higher ionic conductivities are simultaneously achieved in Li${}_{10.5}$Ge${}_{1.5}$P${}_{1.5}$S${}_{12}$ ($\delta =0.5$), exhibiting an ultrahigh room-temperature ionic conductivity of 18.8mS/cm.