Pd-Si System Research Articles

Molecular dynamics simulations of glass formation, structural evolution and diffusivity of the Pd-Si alloys during the rapid solidification process

The atomic structure, glass formation process and diffusion mechanism of Pd100-xSix (x = 10, 20, 30, 40 and 50) alloys during rapid solidification have been investigated by molecular dynamics simulations using embedded atom method potentials. The structure factors, total (or Pd90Si10) and partial pair distribution functions calculated for Pd80Si20 bulk metallic glass are in good agreement with the experimental/other data. Bond angle distribution function, Honeycutt-Andersen index and Voronoi tessellation analysis have revealed that the increasing Si amount caused a decrease in the number of icosahedral-like clusters and an increase in the number of crystal-like clusters. The majority of icosahedral-like clusters in the systems are mostly composed of Pd-centered clusters, suggesting that Pd has an effective role in the glass formation process in Pd-Si systems. It has been observed that the mobility of Si atoms decreases in environments with more Pd atoms. The critical temperature and T0 temperature for Pd-Si liquids have been determined from the self-diffusion coefficients using the mode-coupling theory and the Vogel-Fulcher-Tammann law, respectively. The present findings show us that the Pd70Si30 compound has a critical importance in terms of the glass formation process, which is consistent with experimental observations. We hope that the results will contribute to understanding the Si effect on the atomic local structure of Pd-Si systems and will encourage research on many properties of these systems, such as their mechanical properties.

Diffusion bonding of Ti‐coated Cf‐SiCf/SiBCN composites to Nb using Ag–Pd interlayer

AbstractThe Ti‐coated Cf‐SiCf/SiBCN ceramic was diffusion‐bonded to Nb using an Ag–Pd interlayer. At a ceramic/Ag–Pd interface, it is found that Ti first reacted with C and Pd to form a TiCx/Ti(Pd) double‐layer structure, and then Ti(Pd) completely converted into TiCx with the increase of holding time or temperature. Meanwhile, the infiltration of Pd along TiCx grain boundary reacted with Si to form brittle Pd2Si compound. By contrary, only a simple NbPd3 layer was formed at the Nb/Ag–Pd interface during the whole process. A maximum shear strength of 16 ± 3 MPa is obtained for the joint prepared at 900°C for 30 min. The plastic deformation of the Ag–Pd interlayer and pullout of fibers inside ceramic contributed to the superior performance. Nevertheless, as the holding time and temperature reached 90 min and 950°C, the high chemical affinity of the Pd–Si system and enhanced atomic diffusion led to the massive formation of Pd2Si, which increased the joint brittleness and degraded the ceramic performance.

Structural heritage of metallic glasses and relevant crystals understood via the principal cluster

ABSTRACT Structural heritage between bulk metallic glasses (BMGs) and their relevant crystals has already been acknowledged. But how this kind of heritage is represented is still unclear. In the present paper, firstly, two important characters are considered to determine the principal cluster of crystal, i.e. the atomic-packing efficiency which is evaluated by atomic density radial distribution method and cluster isolation degree which is obtained by the cluster-size reduction rate because of overlapping of clusters in crystal. Then according to these two criteria principal clusters of BMGs Cu-Zr, (Pt,Pd)-Zr and Pd-Si systems are analysed. And the results show that the principal cluster dominates the short-range-order structure of its parent phase as well as the relevant BMG. It is exactly the principal cluster that enters the cluster-plus-glue-atoms units to formulate BMG as [principal cluster](glue atom)1,3. It proves that the structural heritage between glassy state and relevant crystal is actually reflected by cluster formula which contains the principal cluster. Furthermore, via study structural similarity of metallic glass and relevant crystal, elaborated steps towards quantitatively composition design for BMGs are established.

Development of a deep machine learning interatomic potential for metalloid-containing Pd-Si compounds

Interatomic potentials based on neural-network machine learning (ML) approach to address the long-standing challenge of accuracy versus efficiency in molecular-dynamics simulations have recently attracted a great deal of interest. Here, utilizing Pd-Si system as a prototype, we extend the development of neural-network ML potentials to compounds exhibiting various types of bonding characteristics. The ML potential is trained by fitting to the energies and forces of both liquid and crystal structures first-principles calculations based on density-functional theory (DFT). We show that the generated ML potential captures the structural features and motifs in $\mathrm{P}{\mathrm{d}}_{82}\mathrm{S}{\mathrm{i}}_{18}$ and $\mathrm{P}{\mathrm{d}}_{75}\mathrm{S}{\mathrm{i}}_{25}$ liquids more accurately than the existing interatomic potential based on embedded-atom method (EAM). The ML potential also describes the solid-liquid interface of these systems very well. Moreover, while the existing EAM potential fails to describe the relative energies of various crystalline structures and predict wrong ground-state structures at $\mathrm{P}{\mathrm{d}}_{3}\mathrm{Si}$ and $\mathrm{P}{\mathrm{d}}_{9}\mathrm{S}{\mathrm{i}}_{2}$ composition, the developed ML potential predicts correctly the ground-state structures from genetic algorithm search. The efficient ML potential with DFT accuracy from our study will provide a promising scheme for accurate atomistic simulations of structures and dynamics of complex Pd-Si system.

Spherical periodicity as structural homology of crystalline and amorphous states

It has been widely accepted that spherical periodicity generally dominates liquid and amorphous structure formation, where atoms tend to gather near spherically periodic shells according to Friedel oscillation. Here it is revealed that the same order is just hidden in the atomic global packing modes of the crystalline phases relevant to bulk metallic glasses. Among the multiple nearest-neighbor clusters developed from all the non-equivalent atomic sites in a given phase, there always exists a principal cluster, centered by which the spherical periodicity, both topologically and chemically, is the most distinct. Then the principal clusters plus specific glue atoms just constitute the cluster-plus-glue-atom structural units shared by both metallic glasses and the corresponding crystalline phases. It is further pointed out that the spherical periodicity order represents the common structural homology of crystalline and amorphous states in the medium-range through scrutinizing all binary bulk-glass-relevant phases in Cu-(Zr, Hf), Ni-(Nb, Ta), Al-Ca, and Pd-Si systems.

Phase Stability for the Pd-Si System: First-Principles, Experiments, and Solution-Based Modeling

The relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that $${\rm Pd}_{5}{\rm Si}{\text{-}}{\mu }$$ , $${\rm Pd}_{9}{\rm Si}_2{\text{-}}{\alpha }$$ , $${\rm Pd}_3{\rm Si}{\text{-}}{\beta }$$ , $${\rm Pd}_2{\rm Si}{\text{-}}{\gamma }$$ , and $${\rm PdSi}{\text{-}}{\delta }$$ are the stable phases at 0 K (–273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the $${\rm PdSi}{\text{-}}{\delta }$$ phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds $${\rm Pd}_{5}{\rm Si}{\text{-}}{\mu }$$ , $${\rm Pd}_{9}{\rm Si}_{2}{\text{-}}{\alpha }$$ , $${\rm Pd}_{3}{\rm Si}{\text{-}}{\beta }$$ , and $${\rm Pd}_2{\rm Si}{\text{-}}{\gamma }$$ are treated as stable phases down to 0 K (−273 °C), while the $${\rm PdSi}{\text{-}}{\delta }$$ is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. The liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for $${\rm Pd}_{5}{\rm Si}{\text{-}}{\mu }$$ , $${\rm Pd}_{9}{\rm Si}_2{\text{-}}{\alpha }$$ , $${\rm Pd}_3{\rm Si}{\text{-}}{\beta }$$ , $${\rm Pd}_2{\rm Si}{\text{-}}{\gamma }$$ , and $${\rm PdSi}{\text{-}}{\delta }$$ . Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.

Atomic Transport in Nano-Crystalline Silicides Studied by <i>In Situ</i> Auger Electron Spectroscopy: Interfacial Reaction Effect

Silicide growth via reaction between a metallic film and a Si substrate has been well documented. In general, atomic transport kinetic during the growth of silicides is considered to be the same as during equilibrium diffusion, despite the reaction and its possible injection of point-defects in the two phases on each side of the interface. To date, the main studies aiming to investigate atomic transport during silicide growth used immobile markers in order to determine which element diffuses the fastest during growth and in which proportion. The quantitative measurements of effective diffusion coefficients during growth was also performed using Deal-and-Groove-type of models, however, these effective coefficients are in general not in agreement with the interdiffusion coefficients calculated using the equilibrium diffusion coefficients measured during diffusion experiments. In general, atomic transport kinetic measurements during growth and without growth are performed using different types of samples for experimental reasons. In this paper, we discuss the possible use of ultrahigh vacuum in situ Auger electron spectroscopy in order to measure the effective diffusion coefficient during growth, as well as the equilibrium self-diffusion coefficients, in the same samples, in the same experimental conditions. The first results on the Pd-Si system show that atomic transport during Pd2Si growth is several orders of magnitude faster than at equilibrium without interfacial reaction.

The Sr-poor part of the Sr–{Pd,Pt}–{Si,Ge} systems: Phase equilibria and crystal structure of ternary phases

Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of four ternary systems: Sr–{Pd,Pt}–Si at 900°C and Sr–{Pd,Pt}–Ge at 700°C. In the Sr–Pd–Si system the formation of the silicide SrPdSi3 (BaNiSn3-type) was confirmed and a small homogeneity region was found. Furthermore, two novel compounds were detected and their crystal structure was refined from X-ray powder patterns: SrPd0.3Si1.7 (AlB2-type) and SrPd5.9Si6.1 (own-type). In the Sr–Pt–Si ternary system a novel compound with AlB2-type was discovered (SrPt0.3Si1.7), whereas SrPtSi3 with the BaNiSn3-type was confirmed. Two more compounds were detected by EPMA, but their crystal structure remains unknown. In the Sr–{Pd,Pt}–Ge systems no new compounds were observed, but the existence of SrPdGe3 and SrPtGe3 (both adopt the BaNiSn3 structure type), and SrPt4Ge12, crystallizing in the LaFe4Sb12 structure type, was corroborated. For selected ternary silicides the electronic structure was evaluated by DFT calculations.

First-principles study of the Pd–Si system and Pd(0 0 1)/SiC(0 0 1) hetero-structure

First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100K. Various PdSi (Pnma, Fm3¯m, P6¯m2, Pm3¯m), Pd2Si (P6¯2m, P63/mmc, P3¯m1, P3¯1m) and Pd3Si (Pnma, P6322, Pm3¯m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd2Si and D011-Pd3Si fragments, in agreement with experiment.

유성밀 프로세스와 밀링에너지

Milling is a core fabrication process in powder technology. Especially the high-energy milling technology is being frequently used in energy-intensive process like mechanical alloying, mechanical activation and mechanochemistry, etc. Planetary ball mill is a representative highenergy mill together with shaker mill, stirred mill and vibration mill. Since milling condition strongly affects the property of milled powder materials, it should be controlled by changing the milling balls, the milling vial, the geometry of mill, and the rotation speed etc. to obtain an end product with desired characteristics. Milling with large, high density balls and higher rotation speed seems to provide materials with higher impact energy in comparison with small, low density balls and lower rotation speed. It is important to have an understanding the relationship between the milling process variables and the characteristics of final powder products. Many researchers have reported already their results and theories in such aspects. Attempts to modeling the ball mill process have been done in the last decades [1-14]. Burgio et al. [1] has established the fundamentals of mathematic model for determining the impact velocity of the ball and the energy transferred to powder. Padella [6] reported the results from experiments in which the energy transfer was intentionally controlled to form either intermetallic compound or amorphous phase of Pd-Si system. Research works to establish a milling map have pointed out the importance of determining which milling parameters have to be employed in order to obtain a particular final product. This paper reviews the theories of milling energy in planetary ball mill process based on the collision model.

Novel Test Structures for Dedicated Temperature Budget Determination

We present a novel method for determining the temperature budget of the process side of silicon substrates and chips, based on well-known silicide formation reactions of metal-Si systems and (four-point probe) resistance measurements. In this paper, we focus on the Pd-Si system that is most temperature sensitive in the range from 100°C to 200°C. A variety of test structures is introduced to exploit the specific properties of the diffusion-limited reaction between Pd and Si. Among others, this resulted in gap-based layouts that facilitate an extension of the temperature range to 350°C. Designs and measurement results are presented, indicating the practicality and the robustness of the proposed technique.

ChemInform Abstract: Amorphous Magnetic Materials - a History

The discovery of Au-Si and subsequent Pd-Si systems in glassy states had lead to the formation of a number of stable amorphous magnetic materials. A brief history of this development and its scientific and technological significance is given in a somewhat chronological order.

ChemInform Abstract: Alloys of the Pd-Si System, Obtained by Fast Melt Cooling Under Pressure.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Investigation of the Interaction of the Components in the Sm-Pd-Si System.

Abstract A variety of physicochemical analysis techniques was employed in constructing the isothermal section of the phase diagram of the Sm–Pd–Si system at 870 K. Several new ternary compounds Sm 3 Pd 21.7–18.8 Ge 4.3–7.2 , Sm 0.12 Pd 0.63 Si 0.25 , Sm 0.12 Pd 0.58 Si 0.30 , Sm 0.165 Pd 0.72 Si 0.115 , SmPd 2.–1.75 Si 2.0–2.25 , Sm 2 Pd 3 Si 5 , Sm 0.20 Pd 0.25 Si 0.55 , SmPdSi 3 , SmPd 2 Si, SmPd 1.6 Si 0.4 , Sm 0.335 Pd 0.445 Si 0.22 , SmPdSi, SmPd 0.75–0.65 Si 1.25–1.35 , SmPd 0.35–0.20 Si 1.65–1.80 , Sm 3 Pd 2 Si 2 , Sm 0.45 Pd 0.10 Si 45 , Sm 0.50 Pd 0.38–0.30 Si 0 , 12–0.20 were found. The temperature dependences of the specific resistance were investigated for Sm 20 Pd 45 Si 35 , SmPd 2 Si 2 , Sm 20 Pd 38 Si 42 and Sm 20 Pd 35 Si 45. .

A thermodynamic description of the Pd–Si–C system

The Pd–Si–C system was critically assessed by means of the CALPHAD technique. The solution phases (liquid, face-centered cubic, graphite and diamond) were modeled with the Redlich–Kister equation. The compounds Pd 21Si 4, αPd 2Si and βPd 2Si, which have a homogeneity range, were treated as the formulae (Pd, Si) 21Si 4, α(Pd, Si) 2Si and β(Pd, Si) 2Si by a 2-sublattice model with Pd and Si on the first sublattice, Si on the second one, respectively. The intermetallic compounds, Pd 5Si, Pd 3Si, Pd 9Si 2, Pd 14Si 3, PdSi, Pd 39Si 20, Pd 19Si 10, Pd 15Si 4 in the Pd–Si system and SiC in the Si–C system were treated as stoichiometric compounds. A set of self-consistent thermodynamic parameters of the Pd–Si–C system was obtained.

Isothermal cross-section of the Ce–Pd–Si phase diagram at 600°C

The interaction of the components in the Ce–Pd–Si system at 600°C was investigated over the whole concentration range by X-ray powder and single crystal diffraction, DTA, and X-ray microprobe analysis. The formation of the two previously reported phases, CePd 2Si and Ce 2Pd 3Si 5, was not confirmed. There are ten ternary compounds in the Ce–Pd–Si system. The crystal structures of seven of them were determined.

Investigation of the interaction of the components in the Sm–Pd–Si system

A variety of physicochemical analysis techniques was employed in constructing the isothermal section of the phase diagram of the Sm–Pd–Si system at 870 K. Several new ternary compounds Sm3Pd21.7–18.8Ge4.3–7.2, Sm0.12Pd0.63Si0.25, Sm0.12Pd0.58Si0.30, Sm0.165Pd0.72Si0.115, SmPd2.–1.75Si2.0–2.25, Sm2Pd3Si5, Sm0.20Pd0.25Si0.55, SmPdSi3, SmPd2Si, SmPd1.6Si0.4, Sm0.335Pd0.445Si0.22, SmPdSi, SmPd0.75–0.65Si1.25–1.35, SmPd0.35–0.20Si1.65–1.80, Sm3Pd2Si2, Sm0.45Pd0.10Si45, Sm0.50Pd0.38–0.30Si0,12–0.20 were found. The temperature dependences of the specific resistance were investigated for Sm20Pd45Si35, SmPd2Si2, Sm20Pd38Si42 and Sm20Pd35Si45..

Molecular dynamics simulation of local atomic structure in amorphous Pd-Si alloys

The molecular dynamics simulation was applied to a Pd-Si system with constant temperature and pressure. An abrupt volume decrease in the quenching was observed only in the pure Pd system which was due to the crystallization. The atomic radial distribution functions were calculated for these alloys in the quenched states. The local atomic structure was investigated based on analyses of the Voronoi polyhedra. Observation frequency of the Voronoi polyhedra typical of the crystalline Pd increased with the decrease of Si composition and quenching rate. The medium range order (MRO) structures were then recognized as structures with fixed Voronoi polyhedra extending over several atomic distances. As Si composition decreases, the MRO domain increases rapidly. The critical quenching rate for growth of the MRO domain seems to exist between 2.0 × 10 12 K/s and 5.0 × 10 12 K/s in our systems. The nucleation of the MRO structures were influenced by the composition fluctuation of Si atoms. After that, the MRO domain grows by the rejection of Si atoms from the clusters during the quenching process.

In Situ Tem Study of Reactions in Iron/amorphous Carbon Layered Thin Films

ABSTRACTReactions between Fe and amorphous carbon (a-C) below 600ºC have been investigated. In situ annealing in a transmission electron microscopy (TEM) was performed on a-C/Fe/a-C trilayer films deposited by DC sputtering. As-deposited films showed a well defined tri-layered structure and an average Fe grain size of about 50Å. Cementite (Fe3C) grains appeared in the Fe layer by annealing around 300ºC. As the annealing temperature was raised, the number and size of the cementite grains increased. When the annealing temperature reached 500ºC, the Fe layer completely turned into cementite with an average grain size of 1000Å. At this point the film still kept a well defined tri-layered structure even though some parts of the cementitelayer agglomerated. Above 500ºC, the cementite layer started to “move” into the a-C leaving graphite behind. Graphite formed in this process is strongly textured with the (0002) graphite basal planes parallel to the surface of the moving cementite. This process is concluded to be carbide mediated crystallization of a-C, similar to silicide mediated crystallization of silicon in Ni-Si and Pd-Si systems.

Defect profiling in elemental and multilayer systems: correlations of fitted defect concentrations with positron implantation profiles

The results of several positron annihilation (Doppler broadening) experiments have been analyzed using the BNL Monte Carlo implantation profiles and the program VEPFIT. The program VEPFIT has been modified so that scaled, parameterized multilayer profiles can also be used as the initial condition for the diffusion equation solution. We have looked at both elemental (e.g. amorphous silicon) and multilayer (e.g. Pd Si ) systems. Strong correlations between the input implantation profile parameters and the fitted values obtained for the diffusion lengths and overlayer thicknesses for the multilayer systems have been found. The effect of uncertainties in the mean depth on the value of the diffusion length and hence the defect concentrations will be discussed. The impact of reimplanting backscattered positrons on both the implantation profiles and the fitted diffusion lengths will also be presented.