Phenomenological Study Of EOSs And Anharmonic Properties For Solids At High Temperatures-High Pressures

Equation of state (EOS) is an important branch in the field of basic and applied science. EOS is, narrowly speaking, the relationship P=P(V,T) between the pressure P, the volume V and temperature T of substance system in thermodynamic equilibrium, sometimes including the cohesive energy E(V,T). We call P=P(V,T) as pressure equation and E(V,T) energy equation. Study of Thermodynamic theories pointed out that all the thermodynamic properties will be known if we have these two equation, which is just the place where the study of EOS shows very important meaning. Therefore extensively speaking, the theories of EOS are also the theories on thermodynamic properties of substance system. This paper makes a systematic study of EOS and anharmonic thermodynamic properties for solid substance system at high temperatures-high pressures by using phenomenological method.Preface introduces briefly the origins, purposes and conditional scopes of this work, the history of study of EOS and it's applied subject scopes, the methods and measures used in the paper as well as it's theoretical meanings and practical values.The first chapter gives the summary of basic theories of EOS for solids, including often-used thermodynamic theories and phenomenological expressions during the study progress of EOS along with the finite strain theory. Furthermore, from the view of solid-state theory the general expression of EOS of solids P =Pc+Pn is given, and the microcosmic mechanism of compression for solids, i.e., the interactive potential energy between atomics, is also analyzed, subsequently several different forms of cold energies and pressures are derived.Based on the summarizing of three classes of EOSs (isothermal EOS P=P(V), isobaric EOS V=V(T) and complete EOS P=P(V,T)), chapter two complete the following works: ① A new expression of P=P(V,T), i.e., complete EOS, is derived according to SP EOS using the approximation of , being applied to the experimental data for Au, NaCl and CsCl at different temperatures and pressures, and the calculated results agree well with experiment; ② A farther test of universality of several often-used EOSs (TEOS, BMEOS and Vinet EOS) is given by using experimental data of 19 classes of solids; ③ The study of relation between EOSs gives the conclusion that SPEOS, FIEOS, TEOS and Murnaghan EOS are compatible when compression ratio V/V0>0.8; ④In view of the suggestion of Chen and Vinet, we revise Vinet EOS and obtain a new three-parameter EOS. Comparisons with experimental data of seven classes of solids indicate the new EOS is superior to Vinet EOS in validity and has good practical values.Chapter three pays attention to three anharmonic properties, bulk modulus , Grüneisen parameter and thermal expansion coefficient along with their higher order quantity, which is widely interesting to people. Starting from the analysis of quantities of experimental data, we propose some new computing model and formulas on the volume and pressure dependence of, and , i.e., (V,P), (V,P) and (V,P). Comparisons with experimental data make clear that these new computing formulas are all in agreement with experiment and improve the former works in different degree, so they have good validity and reliability.In brief, surrounding EOSs of solids at high temperatures-high pressures, this paper makes worthy explorations on the expressions of EOSs and anharmonic properties of solids, present some new approaches for theoretical predictions of behaviors for solids at high temperatures-high pressures. Certainly, the applications of our results are constrained because of the using of some approximation. The tag discloses this point and several subjects that are worth, we considering, continuing to be investigated on the EOSs and anharmonic properties of solids.