arXiv subjects

John De Poorter

Publications and source records attributed to John De Poorter.

3 recordsLinked to original sources

arXiv2020

An electrodiffusion model for Jaccard's theory in ice

Jaccards' theory describes the movement of both ionic and Bjerrum defects in ice. Standard descriptions of the theory are based on a chain model describing the movement of these defects along well-oriented chains of water molecules. However, this model contains several fundamental contradictions and does not result in the exact equations. We present an alternative model based on the electrodiffusion of the defects. The polarisation of the ice specimen favours these defects orientations that diffuse opposite to the electric drift of the same defect. This straightforward approach not only results in the correct equations, it also provides a better understanding of the defects' kinetics.

cond-mat.soft↗

arXiv2020

An improved interstitial-ice model for pure liquid water

The main idea of the interstitial-ice model is that liquid water consists of an intact hexagonal lattice with both vacant lattice positions and interstitial water molecules. Narten, Danford and Levy derived the model parameters from the X-ray diffraction patterns of liquid water. However, their results were counter-intuitive: their model had almost no vacancies, the interstitial concentration was temperature independent and the ice lattice was deformed resulting in extra anisotropy. To overcome these problems, we refined the model and derived the model parameters from the proton nuclear magnetic resonance frequency of pure water. Without any extra anisotropy, a significant concentration of vacancies was found (3.7% of the lattice positions at 0°C) and the concentration of both the vacancies and interstitials increased quasi linear with temperature (0.05 M/°C). This improved model successfully explains the thermodynamic data of water and is therefore a promising candidate for a coherent and analytical water model.

cond-mat.mtrl-sci↗

arXiv2019

A new and coherent interstitial-ice model for pure water part II: explaining the conflicting Hall data

In part I of this paper the electric behaviour of pure water is described by an interstitial-ice model, the so-called Protonic-Semiconductor Interstitial-Ice or PSII model. Liquid water consists of an intact ice-like lattice with a significant percentage of both vacant lattice positions and water molecules filling the interstitial sites of the open ice-like lattice. It is shown that not the Grotthuss mechanism is dominant in water but a thermally-induced hopping mechanism of the H$^+$ and OH$^-$ ions linked to vacancies. In part II this hopping mechanism is further explored and confronted to the small Hall mobilities of the ions, still unexplained with mainstream models. Two types of complexes are found. The first type is composed of either charged vacancies with the opposite charge of the ion (H$^+$VL and OH$^-$VD) or neutral vacancies (H$^+$V and OH$^-$V). These complexes are responsible for the major part of the mobility of the ions. However, their movement is changing the electric polarisation density of the lattice structure blocking the Hall effect of these complexes. The second type of complexes contains a vacancy charged similar as the ion (H$^+$VD and OH$^-$VL). This second type is responsible for only a small fraction of the electric mobility (10-20%), but their movement is not altering the electric polarisation of the lattice structure. They are responsible for the measured small Hall mobilities of the ions.

cond-mat.mtrl-sci↗