Phase nonmetallic

Fig. 16 (a) Phase diagram of K-(hg-ET)2Cu[N(CN)2]Cl determined from conductivity and magnetic measurements [213, 217, 218], N1-N4 nonmetallic phase, M metallic phase, RN reentrant nonmetallic phase, I-SC-I, II incomplete superconducting phase, S-SC complete superconducting phase. N2 shows the low-dimensional AF fluctuation. N3 shows growth of three-dimensional AF ordered phase. N4 weak ferromagnetic phase, (b) Proposed phase diagram [211, 212]... 

General considerations regarding the character of the transition of a substance from a metal to a dielectric state lead to the conclusion that such a transition occurs as a normal phase transition even up to high temperatures. For mercury and other low-boiling metals the critical point of transition from a liquid to a gaseous state probably corresponds to a lower temperature. One should expect the existence in some region of two separate (at different pressures and temperatures) transitions, from a metallic to a nonmetallic state, and from a liquid to a gaseous state, i.e., the existence of a liquid nonmetallic phase which transforms into a metal with increased pressure, and into a gas with decreased pressure. 

It seems that for a great class of metallic and nonmetallic phases the consideration of two spatial correlations (named simply a binding) is sufficient for the assessment of phase stability. It is therefore appropriate to speak of a two-correlations model which gives the first valence concept for alloys since we know chemical compounds in metallic mixtures. 

Figure 4.13 (a) A typical binary metaUnrgical phase diagram (b) a typical ceramic (nonmetallic) phase diagram... 

Four-probe dc conductivity of ES-I, as a function of protonation level, showed [21] a conductivity proportional to exp[-(T/T)i ]. The slope of the conductivity vs T / curves is independent of dopant concentration for x s [C1]/[N] 0.3. Given the behavior of susceptibility vs. protonation level for the ES-I family, the conductivity is best understood in terms of charging-energy-limited tunneling among the small metal islands [43]. For [C1]/[N] > 0.3, it appears that the barriers between the islands remain the same, while the number of pathways increases. Together wiA the electric field dependence of the conductivity, T can be used to estimate [21] the separation among the metallic islands as 100 A, in accord with later x-ray diffraction studies [20]. The temperature-dependent thermoelectric power, as a function of protonation level, shows a clear crossover in behavior, as a function of protonation level [21]. Analysis of the data is consistent with effective medium theory for a metallic phase embedded in a nonmetallic phase [44]. 

Note the peculiarities of the work functions in a nonconducting medium (vacuum, pure solvent) and a conducting medium (electrolyte solution) when two metals contact each other, an electron equilibrium is always established between them, i.e., the condition te(l) = is met. The work function W is defined as the work of electron transfer from a metal to a point in the nonmetallic phase which is in the proximity to the interface at such a distance that the potential variation with distance can be ignored, i.e., beyond the superficial electric double layer, including the region in which the image forces are active ... 

When the nonmetallic phase is nonconductive, the potentials on the surface of both metals are not equal. This potential difference, the Volta potential Ai/r, makes an appropriate contribution to the electrochemical... 

If the nonmetallic phase is highly conductive, the potential in this phase, at any point beyond the double layer, is the same hence, the electrochemical potential, /LCe(Nm), is the same, too. Therefore, the electronic work function in metal-solution systems for two metals which are in direct or indirect contact (i.e., at the same electrode potential) is the same. It stands to reason that this applies equally well to different faces of the same metal. 

Electrocrystallization of a nonmetallic phase can be a secondary effect, arising when saturation of the electrolyte by the product of the electrode reaction is reached. It can, however, also result from direct formation of the product by a solid state reaction. 

The other major difference between fluid metals and semiconductors concerns the phase behavior and the electronic character in various regions of the temperature-density plane. The low-temperature liquid-vapor equilibrium of semiconducting liquids involves two nonmetallic phases whereas the vapors of metallic elements are, by definition, in equilibrium with a liquid metal phase. The metallic state develops in fluid semiconductors when the temperature and pressure are high enough to disrupt the structural order responsible for semiconducting electronic structure. If this occurs near the critical region, there exists the possibility of rapid MNM transitions and strong interplay between the electronic properties and critical density fluctuations. In this respect, fluid metals and semiconductors behave similarly under extreme conditions whereas they are markedly different near their respective triple points. 

Patterson, J.W., Ionic and electronic conduction in nonmetallic phases, in ACS Symposium Series No. 89, Corrosion Chemistry, Brubaker, G.R., Beverley, P., and Phipps, P.P., Eds., American Chemical Society, Washington, D.C., 1979, 96-125. 

---