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The equilibrium concentration of vacancies í µí± in Au cluster on graphite at T=300 K relative to the atomic density í µí± 0 calculated as function of cluster height h.
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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 s...
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Context 1
... the equilibrium concentration of vacancies in a cluster í µí± taking into account the cluster-substrate interaction. The theoretical dependence of the relative concentration of vacancies for Au cluster on graphite surface as function of cluster height at room temperature (Т=300 K) calculated from the equations (6), (8) and (9) is plotted in Fig. 1. It is seen that the concentration of vacancies sharply increases for cluster height less than 22 Å, that can result in the modification of the modulus of elasticity of cluster and, as a consequence, to the shifts of the lattice parameter and the melting point ...
Context 2
... (6), (8), (9), (10) and (12) allow to calculate the dependence of the lattice parameter on cluster height. Such dependences for the clusters of Cu, Au and Ag deposited on graphite at room temperature are presented in Fig.3. The parameters used in the calculations of the dependencies plotted in Figs. 1-3 are summarized in Table 1. The energy of vacancy formation in the volume, eV 0.9 [23] 1.11 [15] 1.28 [15] The energy of vacancy formation at the surface, eV 0.25 [23] 0.16 [15] 0.35 [15] Divacancy formation energy [23] , eV 0.1 0.1 ...
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Citations
BiVO4/Bi4V2O11 heterojunction sensing materials for the mixed-potential NH3 sensor were prepared by the hydrothermal method and sequent heat treatment, accompanying self-phase separation. The influence of the Bi³⁺/V⁵⁺ mole ratios on phase composition, microstructure of sensing materials and the performances of the sensor was investigated. The samples with different Bi³⁺/V⁵⁺(1:1-2:1) calcined at 500 °C form non-stoichiometric Bi4V2O11 and Bi2VO5.5 and further calcination at 750 °C, all samples change into BiVO4/Bi4V2O11 heterojunction materials. The mixed potential sensors based on above-mentioned heterojunction materials and Ce0.8Gd0.2O1.9 electrolyte show excellent performance. The sensor based on sensing electrode with Bi³⁺/V⁵⁺=1.75:1 can stably work at 450-600 °C due to good porous structure of sensing electrode, which is conducive to gas diffusion and adsorption. At 500 °C, the sensor has the highest sensitivity and the lowest detection limit. The relationship between ΔV and logarithm of NH3 concentrations is piecewise linear in the range of 1-25 ppm and 25-300 ppm, and the sensitivity is -6.9 and -38.2 mV/decade, respectively. The cross-sensitivity test of the sensor shows that co-existent gas CO2, CH4, H2 or H2S makes the response value change -3.7%, -3.0%, 0.9% and -6.8%, showing good anti-interference performance to these gases. While NO or NO2 causes serious interference, making the response value reduce by -9% and -27%. CuO instead of Pt as the reference electrode nearly eliminates the interference of NO and NO2. In addition, sensor following the mixed potential mechanism was confirmed by experiments.
Carbon supported Pt nanoparticles with diameters ranging from 2 to 28 nm have been studied using X-ray diffraction. The unit cell parameter of synthesized Pt/C nanoparticles is always lower than that of bulk Pt. By decreasing the average particle size D to approximately 2 nm, the unit cell parameter a nonlinearly decreases by about 0.03 Å which corresponds to a variation of 0.7% in comparison to bulk Pt, and the size effect is predominant for sizes ranging from 2 to 10 nm. The dependence a(1/D) is approximated well using a straight line with a slope of −0.0555 ± 0.0067 nm−1 and an intercept of −3.9230 ± 0.0017 Å. For interpreting the obtained experimental dependence of the unit cell parameter of Pt/C nanoparticles, four different theoretical approaches such as the thermal vacancy mechanism, continuous-medium model, Laplace pressure, and bond order–length–strength correlation mechanism, were used. Comparison of the calculated dependencies, based on the above models, with the experimental ones, shows that the continuous-medium model agrees best with the experimentally found unit cell parameter dependence of our carbon supported Pt nanoparticles.
Within the limits of the uniform approach with the assistance of the vacancy mechanism the description of melting and surface roughening of both free nanoparticles and nanoparticles deposited on the surface of solid body under conditions of thermodynamic equilibrium is offered. Surface roughening of a spherical particle is represented as a phase transition in vacancy subsystem, in which supersaturation is formed by reducing the particle size. It is shown that interaction between vacancies result in to the unification of vacancies on a surface in vacancy clusters, that can be regarded as the appearance of a surface roughness of nanoparticles. It is shown that increasing concentration of vacancies caused by the modification of effective vacancy formation energy with decreasing sizes of nanoparticles result into a modification of shear modulus of material. By vanishing the shear modulus (Born criteria of melting) the dependence of temperature of fusion of nanoparticles of different metals on radius was determined.
P-type higher manganese silicide (HMS) has attracted considerable interest due to its remarkable thermoelectric (TE) properties and potential applications at intermediate and high temperature TE devices. In this study, a series of nanostructured bulk p-type HMS materials with different compositions of MnSix (where x=1.73, 1.75 and 1.77) were synthesized via mechanical ball milling and hot-press sintering. The X-ray diffraction analysis of the synthesized materials showed that increasing the Si contents yields to a slight shift to higher diffraction angles. The increase in Si content further resulted in a decrease in electrical conductivity and increase in Seebeck coefficient. The power factor of all three compositions are approximately identical. However, the lowest thermal conductivity was achieved in MnSi1.75 and resulted in the highest figure-of-merit among all the compositions.
