Elastic Properties Of Pd_3-x Rh_xV Alloys

Palladium alloys are consistedof Palladium (Pd) and other metal elements. Palladium alloys have high melting points, low densities, good corrosive and oxidation resistances, their thermodynamic and chemical stabilities are also excellent, so they have increasing application in the electrical cantact materials (slip-ring, electrical brush, contact, commutating segment, rectifying equipment materials), electric resistance materials (capacitive coupling, stress-strain, temperature measuring and thermoelectric materials), medical appliance, gas purification, vessel materials, accouterment and brazing and soldering materials. At present, the reseach on the Pd based alloys are relatively scarce, especially in structural and mechanical properties of the Pd-V alloys and Pd based ternary alloys.First-principles calculations have been thought as a mature and successful tool for the study of the electronic structures and mechanical properties of alloy materials. So this paper uses first-principles calculations to investigate the structural, elastic and electronic properties of Pd₃-xRhxV alloys. Firstly, we perform a systematic study on the electronic structure, and elastic properties of L1₂ - and D0₂₂ -structure Pd₃V by first-principles calculations. Secondly, we carry out a systematic first-principles investigation of the electronic structure and elastic properties of ternary Pd-based alloys (Pd₂RhV, PdRh₂V). The main contents of our work are as follows.(1) In chapter 1, pure Pd and Pd-based materials and its application were introduced, and the advantages (or disadvantages) and actual states of pure Pd and Pd-based materials were also analyzed according to the application and development of Pd-based materials, the main research work of this dissertation was clarified.(2) In Chapter 2, the Vienna ab-initio simulation package (defined as VASP) that were widely used in density functional calculations, were briefly introduced, including the VASP theoretical foundation, basic structure and computational method.(3) First-principle calculations are carried out to investigate the structural, elastic and electronic properties of L1₂ - and D0₂₂- structured alloys Pd₃V in the chapter 3. The related parameters, such as the total energy, formation heat (ΔH)) and cohesive energy of the two kind of Pd₃V crystals were calculated to evaluate the stability. The calculated results show good accordance with experimental results. And the results aslo indicat that the total energy, formation heat (ΔH)) and cohesive energy of Pd₃V alloy for L1₂ structure were higher than that of D0₂₂ structure, indicating that Pd₃V alloy with L1₂ structure is less stable than D0₂₂ structure, so the D0₂₂ structural ability of Pd₃V alloy is stronger. Moreover, the elastic constants (Cij) of Pd₃V with L1₂ and D0₂₂ structure were also investigated. On the other hand, according to the the elastic constants above, the bulk modulus (B), Young's modulus (Y) , shear modulus (G), and Poisson's ratio (ν) of these alloys were calculated. The elastic properties of Pd₃V alloy with D0₂₂ structure were aslo higher than L1₂ structure.(4) In chapter 4, the structural, elastic and electronic properties of ternary Pd-based alloys (Pd₂RhV, PdRh₂V) were also studied by first-principles calculations. The results indicate that the addition of Rh in Pd₃V alloys leads to decrease in the constants and cell volume(both in L1₂ and D0₂₂), and the size of crystal become lower, so the structure to become more stable. In addition, the formation heat and cohesive energies indicate the L1₂ and D0₂₂ ternary Pd-based alloys have better alloying ability, and structural stabilitis become better because of the additon of Rh component. In addition, the elastic constants Cij and elastic modulus including the bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson's ratio (ν) were also calculated, and the results indicat that the addition of Rh indeed improve the mechanical properties of the alloys, especailly PdRh₂V alloys.(5) In chapter 5, the main conclusions of the present investigations are summarized, and according to the obtained results , the development prospect of Pd-based alloys are also outlined.The calculation results in this dissertation would provide theoretical instruction and valuable evidence for further study, development and application of Pd-based alloys.