Difference In Atomic Volume Research Articles

Structure peculiarities of binary state diagrams of vanadium with neighboring elements of Mendeleev’s periodic table

Data on search for correlations between a structure of state diagrams of binary systems based on V-Me (Me = Ti, Zr, Hf, Nb, Ta, Cr, Mo, W) and crystal-geometric and crystal-chemical parameters were presented. Manifestation of both positive and negative deviations in experimental concentration dependences of the atomic volume in solid solutions in systems V-Me (Me = Ti, Nb, Ta, Cr, Mo) from Zen’s law was established. It was found that in the systems with unbounded regions of solid solutions, the deviation from Zen’s law is insignificant. A correlation was found between the types of state diagrams and the difference in atomic volumes of alloy-forming elements in systems V-Me (Me = Ti, Nb, Ta, Cr, Mo).

(Invited) Isotopically Programmed Group IV Semiconductors: A Versatile Platform for Quantum Technologies

The introduction of stable isotopes as an additional degree of freedom in the growth of semiconductor films and quantum structures provides a wealth of opportunities to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. In this presentation, I will describe the historical context and outline the recent progress in the area of isotopically engineering group IV semiconductors with focus on nanoscale and quantum structures and devices. This ability to isotopically program semiconductor structures has been a powerful paradigm to investigate and manipulate some of the important physical properties of semiconductors and exploit them in innovative device structures [1-13]. Isotopes of an element differ in the number of neutrons in the nucleus. This creates differences between the isotopes in their lattice dynamics and nuclear properties. For instance, the slight difference in zero-point motion leads to a difference in atomic volume between the isotope atoms, which influences the lattice constant [3]. Also, the difference in electron-phonon coupling between crystals of different isotopic composition was found to affect the electronic band gap [4]. The nuclear spin is another significant difference between stable isotopes. For instance, natural silicon (Si) has three stable isotopes: 28Si, 29Si, and 30Si, with isotopic abundances of 92.23%, 4.67%, and 3.10%, respectively. Among these three isotopes, only 29Si has a nuclear spin of ½, whereas 28Si and 30Si are nuclear spin-free. This property has been crucial in the realization of Si-based quantum information devices [5-8]. One of the most drastic isotope related effect in semiconductors is found in phonon properties [9-13]. Mass fluctuation induced by isotope disorder acts as a substitutional defect in a crystal thus affecting the phonon mean free path and consequently the phononic thermal conductivity. Measurements on isotopically pure Ge [9] and Si [10] crystals showed an enhanced thermal conductivity as compared to their natural counterparts. Also, lower thermal conductivity was recently demonstrated in Si isotope superlattices [11]. All the properties of semiconductor stable isotopes have been investigated and exploited in bulk materials or thin films. Herein, we will describe the new opportunities emerging from the combinations of the isotope effects with size-related effects in nanoscale materials [14-18]. More specifically, we will discuss phonon engineering in metal catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane and german precursors 28SiH4, 29SiH4, 30SiH4, 74GeH4 and 76GeH4, with purity better than 99.9%. Isotopically mixed nanowires 28Six 30Si1-x with a composition close to the highest mass disorder (x ~ 0.5) were used as a playground to elucidate the interplay between nanoscale interface phenomena and heat transport [16]. We will show how isotopically engineered nanowire homo-junctions can be introduced to realize innovative phononic devices such as thermal diodes and thermal transistors. Additionally, we will also discuss the use of nuclear spin-full 29Si to engineer novel quantum devices in nuclear spin-free SiGe nanostructures. Finally, atomistic-level investigations of isotopically programmed nanoscale materials will be presented based on laser-assisted atom probe tomography [15,17].

Underpotential Codeposition of Au-Ni Alloys: The Influence of Applied Potential on Phase Separation and Microstructure

Au-Ni alloys were electrodeposited from sulfate-based, weakly complexing electrolytes with various Ni concentrations. EQCM data show that by co-deposition with Au, Ni electrodeposition is strongly depolarized and deposition rate is greatly enhanced at a given potential. Composition analysis for alloy films confirms that Ni is incorporated into the alloys at potentials more positive than its own redox potential. A continuous shift of the alloy reflections (111) and (200) was observed by X-Ray Diffraction, which is consistent with the formation of a series of solid solutions, in stark contrast with the immiscibility expected by the thermodynamics of the bulk alloys. HR-TEM for alloy films of ∼60% Ni shows a grain size of less than 15 nm of Au rich grains, and smaller (2–3 nm) Ni-rich grain boundaries with poor crystallinity. This unexpected configuration is probably originated by the attractive interaction of Au and Ni at the solid/electrolyte interface during growth, compensated over time by the strain energy originated by the difference in atomic volumes. The resulting nanoscale decomposition suggests the possibility to tailor atomic configuration and therefore properties via tailoring of the deposition parameters.

First-principles calculation of the pressure dependence of phase equilibria in the Al-Li system.

The solid-phase portion of the Al-Li phase diagram has been computed from first principles both at zero pressure and at a hydrostatic compression of 5.4 GPa. Computation of the pressure dependence of the Al-Li phase equilibria answers two questions: (1) how important is the effect of the atomic size difference, and (2) is the stability of the ${\mathrm{Al}}_{3}$Li precipitates influenced by high hydrostatic stress. The zero-pressure first-principles phase diagram exhibits excellent qualitative agreement with experimental data. The presence or absence of solid solutions (SS), of stable and metastable intermetallic phases, and their degree of order are computed correctly. Compression is predicted to affect the phase equilibria in Al-Li as follows: (1) the solubility of Li in fcc Al-rich SS is decreased, (2) the solubility of Al in Li is increased. However, the low melting point of Li limits the range of SS, and (3) the metastable ${\mathrm{Al}}_{3}$Li Al-rich fcc SS phase equilibrium is unaffected and the stability of the precipitates is unchanged, (4) the ordering tendencies at Li-rich compositions are slightly enhanced. Although high pressure eliminates the difference in atomic volume of the pure constituents, it has almost no effect on the solid-solid phase equilibria in this alloy system. A simple method for verifying the accuracy of the cluster expansion for the configurational internal energy is presented and applied. Moreover, it has been shown that with a convenient choice of the occupation numbers, one can define correlation functions which greatly facilitate the determination of new ground state structures. \textcopyright{} 1996 The American Physical Society.

Radiation-induced atom separation in alloys

Abstract A mechanism of non-uniform concentration region formation in the path of collision cascades in alloys is proposed. Analysis of kinetics of recovery of the post-cascade defect distribution in the alloys shows that annealing of such a damage region can lead to redistribution of the alloy component composition: a region rich in one species of alloy components is formed in the place of a depleted zone. The atoms of one of the components preferentially return due to the significant flux of these atoms to the depleted zone. The flux is caused by difference in component atomic volumes and local stress fields produced by vacancies and interstitials in the post-cascade damage zone. The greater the difference in the atomic volumes the more effective is the formation of non-uniform concentration regions. These regions can be considered as nuclei of a new phase. The mechanism is qualitatively proved by experimentally observed regularities of phase transitions in irradiated alloys.

On the spontaneous volume magnetostriction of iron

It is suggested that the difference in atomic volume between the ferromagnetic and paramagnetic states of iron as estimated from the concentration dependence of the lattice constant for V-Fe and Al-Fe alloys is not necessarily inconsistent with the temperature variation of the lattice constant for pure iron, as had been argued by Shiga and Nakamura (ibid., vol.8, p.177, 1978). A reasonable figure for delta V/V would be about 1.9%, which is consistent with our own previous theoretical value obtained on a simple itinerant-electron model. This fact implies that above the Curie temperature the magnetic state of iron atoms is similar to what it is in paramagnetic V-rich V-Fe alloys, which show no sign of there being a local moment.

Forces acting on misfit dislocations during interdiffusion

Abstract The behaviour of misfit dislocations introduced to accommodate differences in lattice parameter at the interface between two epitaxially oriented crystals of different materials is studied as a function of the degree of interdiffusion of the constituents. The forces considered to be acting on the dislocations are the elastic interaction force between misfit dislocations, the homogeneous force arising from the difference in atomic volume of the constituents, and the osmotic force produced by the net vacancy flux accompanying interdiffusion. In the elasticity calculations, image forces and end effects, including buckling terms, are analysed. The results are compared with prior treatments of related problems, all of which have involved different boundary conditions, and none of which has included considerations if the osmotic force together with the other forces.

Concentration fluctuations in conformal solutions and partial structure factor in alloys

It is shown that the long wavelength limit of the partial structure factors a11, a12 and a22 contains direct information on the non-ideality of the mixture. In particular, the energy of interchanging an A atom and a B atom in two pure substances A and B is reflected rather directly, as is the difference in atomic volumes between atoms A and B. To illustrate the way the non-ideality is reflected in the partial structure factors, the authors have adopted the model of conformal solutions. They demonstrate that the interchange energy referred to above is directly related to the combination 2a12-a11-a22 of the partial structure factors, which is a simple function of c(1-c) in this theory, c being the concentration. The model is applied to Na-K alloys, recently analysed thermodynamically by McAlister and Turner. It is able to explain the principal features of their results. On the other hand, the model is inappropriate for the other case, K-Hg they considered, presumably because the differences in the forces between different species are too large.

Long-range order and ordering kinetics in CoPt3

The Co-Pt system is well suited for studies of order-disorder by field-ion microscopy. Because of this, and the fact that detailed information on ordering is available for only one Ll2 alloy (Cu3Au), an extensive X-ray study was made of CoPt3. Long-range order falls to lower values (S ≈ 0.64) in this alloy than in Cu3Au. There is a two-phase field nearTc (685°C) extending for about 20°C. The ordered phase has a smaller lattice parameter than the disordered phase close toTc, but at room temperature the reverse is true. Ordering (when the domain size is large) follows Rothstein’s kinetic theory, with an activation energy of 74.0(9) kcal per g-atom. Domain growth is similar to grain growth, with a time exponent of about 0.45 and an average activation energy of about 62 kcal per g-atom. The antiphase domain structure is isotropic, in contrast to Cu3Au. There is little difference in atomic volume of cobalt and platinum in the ordered state as compared to the pure elements.

Isotopic mixtures of solid helium

On the assumption that the energy of solid helium is composed additively of the energies of individual atomic cells, that the latter consists of a zero-point energy, a lattice potential and a pressure term, and that the zero-point energy varies inversely as the mass of the atom, it is possible to obtain expressions for the distortion of the lattice around an isotopic impurity, and for the heat of mixing of isotopes of solid helium, in terms of the difference in atomic volume of the two pure solid components and of their elastic constants. It is estimated that at 30 atm the radial distortion around an isotope is 3%, and the heat of mixing is given by H E = X(1 − X) E M , where X is the concentration of one species and E M / R = 0.75° K. The observed value of E M/ R is 0.76°K. Both the distortion and the heat of mixing should decrease with increasing pressure.

Electrical Resistivity of Liquid Sodium, Liquid Lithium, and Dilute Liquid Sodium Solutions

The three factors of atomic size, ion core potential, and charge, which contribute to the increment in electrical resistivity produced by solutes in metallic solutions, have been separated and experimentally evaluated in liquid sodium. The results may be expressed in a semiempirical relationship defining the increment in resistivity of a monovalent solution, Δρ=0.063 | Δ Atomic Number | +0.53 (ΔV/V)2, μohm cm/at. %, where ΔV/V is the fractional difference in atomic volume of solute and solvent and the first term involves the absolute value of the difference in atomic number of sodium and the solutes lithium, potassium, cesium, rubidium, silver, and gold.

On Simple Binary Solid Solutions

The effect of difference in atomic volume between two components of a simple binary solid solution on the phase equilibrium curves is investigated by calculating the energy of deformation required to replace a smaller atom by a larger atom, and vice versa. The strain energy is introduced to the free-energy function derived by the quasi-chemical technique of Guggenheim and leads to expressions similar to those of Hildebrand for unsymmetrical segregation. In addition, the Mie-Gruneisen equation is used to estimate the effect of vibrational entropy changes. It is found that the effect of such changes has a smaller effect on phase equilibria in general than the energy changes. Finally, the results are used to justify certain empirical thermodynamic expressions.