Pierre Damay

Asymmetry of the coexistence curve in binary systems. Size effect

The asymmetry of the coexistence curve in binary systems is either due to a difference of size between the components or to mixed fields as seen in the liquid–vapor case. The size effect may be corrected if the proper order parameter is used. Taking advantage of the many formal possibilities of choosing the order parameter in these systems, we show that the size effect may be exactly corrected for asymmetric mean field models. Making the same type of calculation on real systems with critical indices, we found that the same type of correction is possible. In these cases, there were no mixed field effects detected (t1−α divergence of the diameter), at least in a reduced temperature range t<0.02. The details of the calculation are reported only for acetonitrile–cyclohexane system which is one of the best sets of data found in literature. A new computing method to determine the parameters of the coexistence curve is also presented. The shape of the coexistence curve, including extended scaling correction, as ...

Dielectric anomaly at the metal-insulator transition as seen by electron spin resonance 1. Analysis of the ESR line shape for poor conductors

Abstract The shape of the electron spin resonance (ESR) line for itinerant electrons is asymmetric. The asymmetry is due to a microwave phase shift inside the sample. A complete equation for the power absorbed in conducting media is derived in this paper; it includes spin diffusion, sample size and displacement-current effects. This new formalism is appropriate to study the ESR of heavily doped semiconductors. It is shown that ESR may be a powerful technique to measure the dielectric constant in these media. An application to the study of the dielectric anomaly in lithium-ammonia solutions is given in Part 2 of this paper.

Dielectric anomaly at the metal-insulator transition as seen by electron spin resonance 2. Application to lithium-ammonia solutions

Abstract A formalism appropriate to the analysis of the electron spin resonance (ESR) lineshape in poor conducting media has been derived by us previously. It has been shown in particular that it should be possible to measure the dielectric constant from ESR in doped semiconducting media. This formalism is applied to the study of the non-metal to metal transition in lithium-ammonia solutions. Agreement between actual and theoretical lineshapes has been found. From the results given in the present paper, solutions of lithium in ammonia at 240 K may be separated into three concentration ranges. Firstly, an ‘insulating’ range below 1.5 mole per cent of metal (MPM) with evidence of a dielectric anomaly. Secondly, a metallic range above 3 MPM; even when the conductivity is relatively low, the screening is of Thomas-Fermi type and the dielectric effect rapidly becomes negligible. Finally, in the intermediate range, a dramatic decrease of the dielectric constant towards large negative values is observed; this re...