Systematically Study Of Electronic Structures, Physical Properties And Thermodynamic Properties Of Transition Metals In Ⅰ,Ⅳ And ⅥB Group

The theory of pure elements in the framework of systematic scienceof alloys(SSA)has been improved in this paper, the electronic structures, physical properties and thermodynamic properties of fcc, hcp and bcccrystals of transition metals inⅠB,ⅣB andⅣB groups have beenstudied using this theory, and the theoretical analyses system of pureelements, the knowledge database and information database have beenestablished.In this paper, the following researches on metals inⅠB,ⅣB andⅥB groups have been performed: (1) the electronic structures of stableand metastable phases of transition metals have been calculated, physicalproperties including potential curve, cohesive energy, bulk moduli, Debyetemperature, isometric heat capacity, vibrating energies of lattice, atomicvolume, atomic vibrating energies and atomic potential, andthermodynamic properties including isobaric heat capacity, enthalpy, entropy and Gibbs energy from OK to melting points have been calculatedunder the assumption of the temperature independence of electronicstructure; (2)the electronic structures of liquid phases have beencalculated with the assumption that the liquid phase at melting point havethe same structure with that of solid phase, and the Properties from OK tothe boiling point, have been calculated; (3) the comparison of electronicstructures between one-atom(OA)method of chemical bonding theoryand energy band theory in first principles have been performed and therelationship between electronic structure and crystalline structure hasbeen analyzed; (4) the knowledge database of pure elements includingseries of calculation formulas of various properties such as single bondradius, lattice constants, cohesive energies, bulk moduli and thermalexpansion coefficients have been established; (5) the information databaseof pure elements including data tables of electronic structures, cohesiveenergies and lattice constants of basic atom states, triangles ofhybridization of basic atom states and tables and figures of temperaturedependence of physical and thermodynamic properties of fcc, hcp and bcc crystals and liquids of each elements inⅠ,ⅣandⅥB groups have beenestablished and it provides the basis for the establishment of periodictable of electronic structures and property database of fcc, hcp and bcccrystalls of elements.This paper is focused on the research of relationships betweenelectronic structures and crystalline structures during phase transitions ofpure metals and their influences on the physical and chemical properties.The results of this paper show that (1) in the three criterions of valentelectron density T_c,X_c and T_f, the linear density X_c is a more superiorcriterion than the bulk one T_c for the assessments of mechamic propertiesof metals, while the bulk density of free electrons T_f can be used as auniversal criterion for the assessment of transporting properties of metals, and the combination of T_f and X_c in the nearest covalent bond, i.e. X_c.1, can provide the best criterions for composition selection in alloy design; (2) the studies on the elements Cu, Ag and Au inⅠB group show that theelectronic density decides the physical properties of metals, on one hand, the larger the density of covalent electrons, the stronger the cohesion ofatoms, the higher the melting point, and the better the compressionresistivity, but the transporting properties are weakened at the same timedue to the blocking of the covalent electrons, on the other hand, the largerthe density of free electrons, the better the plasticity, elongation, electricaland thermal conductivity, but the cohesive properties are weakened due tothe less number of cohesive electrons; and it is found as well that the freeelectrons in s orbital of atoms are influenced by the scattering of thecovalent electrons in both d orbital and s orbital and the vibrating ofatomic nucleus, and it is the covalent electrons in s orbital that mainlyinfluence the transporting function of free electrons in liquid phase; (3)the axial ratios of c/a of Ti, Zr and Hf inⅣB group deviate from the idealvalue, so the crystalline symmetry is low, and the linear density ofcovalent electrons X_c is defined for its application in the research of therelationship between electronic structures and physical properties of hcpphase with the combination of T_f and other bond parameters, and theresults show that the symmetry of d_c electrons is lower than that of s_celectrons, and not only the direction and selection of atom coordination of d_c electrons is stronger but also the number of d_c electrons is more thanthat of s_c electrons, so the hcp structures of Ti, Zr and Hf with c/a beingrespectively 1.5884, 1.5925 and 1.5821 can be formed at low temperature; at high temperature, the electrons in d orbital are transformed into sorbital, so the s electrons play main role in the lattice stability and the bccstructrue can exist stablely; (4)using the criterions T_c, X_c和T_f to the studyon the elements Cr, Mo and W inⅥB group, it is found that theproperties such as melting points, tensile strength, hardness, bulk moduliand the bonding energy of the strongest bond follow the same rule as thelinear density in the nearest covalent bond X_{c, 1}, i.e., X_{c, 1} (Cr)＜X_{c, 1} (Mo)＜X_{c, 1} (W), and the electrical conductivity, thermalconductivity and the bonding energy of the free electrons follow the samerule as the the bulk density of free electrons T_f, i.e., T_f(Cr)＜T_f(Mo)＜T_f(W); the analyses of electronic structures of elements Cr, Mo and W inⅥB group show that bcc structure is probable to betransformed into hcp or fcc structure and bcc is more preferred to betransformed into hcp due to the more covalent electrons with strongerbonding ability in d orbital and the less covalent electrons with weakerbonding ability in s orbital in hcp than fcc phase, which causes lowerpotential and higher stability of hcp structure, this result agrees well withthat of SGTE database and can explain the difference of lattice stability inSGTE database from the level of electronic structure; (5) when the solidphase of transition metals inⅠ,ⅣandⅥB group is transformed intoliquid phase, both the nonbonding electrons in d orbital and the covalentelectrons in s orbital increase, the covalent electrons in d decrease, andthe free electrons in s orbital have no obvious change or decrease, thischange of electronic structures leads to the decrease of bonding electrons, weakening of bonding direction and cohesion of atoms, increase of singlebond radius and atomic volume, decrease of the density of free electronsand corresponding decrease of electrical conductivity of liquid phase.