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Electrical Conductivity Measurements of Lithium-Ammonia Solutions Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 8-2003 Electrical Conductivity Measurements of Lithium-Ammonia Solutions Mariana Constantin Barbu Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Physics Commons Recommended Citation Barbu, Mariana Constantin, "Electrical Conductivity Measurements of Lithium-Ammonia Solutions" (2003). Master's Theses. 4260. https://scholarworks.wmich.edu/masters_theses/4260 This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. ELECTRICAL CONDUCTIVITY MEASUREMENTS OF LITHIUM-AMMONIA SOLUTIONS by Mariana Constantin Barbu A Thesis Submitted to the Faculty of The Graduate College In partial fulfillment of the requirements for the Degree of Master of Arts Department of Physics Western Michigan University Kalamazoo, Michigan August 2003 Copyright by Mariana Constantin Barbu 2003 For my Dad ACKNOWLEDGMENTS I would like to give thanks to my advisor, Dr. Clement Bums, for his help and support while working on the project, and forwriting the thesis. I would also like to thank Dr. Lisa Paulius for reviewing my thesis, and providing valuable input. Her help and support were important in my work. I want to express my thanks to Dr. Dean Balderson in my own way. If I could go back in time, I would do things differently. I consider myself lucky having a friendlike Valentina Tobos. Thank you, Valentina for everything. A special thanks goes to Allan Kem, who was always helpfuland nice. I would like to thank David Hoogerheide and Lucian Undreiu. Thanks, you guys. Dave, it was a pleasure to work with you. And most of all, I would like to thank my husband Paul, forputting up with me, and my tantrums, while working on this thesis. ii ELECTRICAL CONDUCTIVITY MEASUREMENTS OF LITHIUM-AMMONIA SOLUTIONS Mariana Constantin Barbu, M.A. WesternMichigan University, 2003 The topic covered in this thesis is the study of electronic interactions forliquid metal-ammonia solutions, lithium-ammonia solutions in particular. To obtain a theoretical understanding of so-called correlated electron systems. The work focuseson sample creation and measurement of electrical conductivity of lithium-ammonia solutions varying with temperature fordifferent concentrations. We have taken measurements in liquid lithium-ammonia mixtures using four-wire method to minimize the contact resistance. We have shown how it is possible to carry out accurate measurements of the electrical conductivity in these systems with the four wire measurements. CONTENTS ACKNOWLEDGMENTS ................................................................................................. ii LIST OF FIGURES .......................................................................................................... iv LIST OF TABLES ............................................................................................................. V CHAPTER I. INTRODUCTION ............................................................................................ 1 Background and History of Metal-Ammonia Solutions ................................... .1 Study of Metal-Ammonia Solutions .................................................................. 3 II. PROPERTIES OF Li-NH3 ................................................................................ 9 Metal-Ammonia Solutions as Electrolytes ........................................................9 Solvated Electron Model.................................................................................. 10 Scattering Model .............................................................................................. 14 Metal-Nonmetal Transition Models ................................................................. 16 Properties of Metal-Ammonia Solutions ........................................................ .17 III. EXPERIMENT AL PROCEDURES ............................................................... 22 Electrical Transport Measurements ................................................................ .22 Temperature Control and Measurement .......................................................... 26 Sample Preparation Details .............................................................................. 29 AlternativeSample Preparation and Preliminary Work ..................................39 IV. EXPERIMENTAL RESULTS ........................................................................ 43 V. CONCLUSION ............................................................................................... 58 VI. BIBLIOGRAPHY .......................................................................................... 59 Ill LIST OF FIGURES 1. 1 Picture ofphase separation in sample with concentration of5 MPM ......................... 6 1.2 Phase diagram forlithium-ammonia solutions ............................................................ 6 2.1 Steps in the salvation of an electron in liquid ammonia ........................................... 10 2.2 Schematic ofthe solvated lithium cation and so.lvatedelectron .............................. 13 3.1 Two-lead versus four lead configuration................................................................... 22 3.2 Block diagram ofresistivity set-up ........................................................................... 24 3.3 Simplified electrical circuit ....................................................................................... 25 3.4 Temperature control and measurement system ......................................................... 27 3.5 Diagram ofpressure control system principle ........................................................... 31 3.6 Purification system .................................................................................................... 32 3.7 Design ofthe conductivity cell .................................................................................. 33 3.8 Picture ofthe ammonia condensation system with sample cell attached .................. 34 3. 9 Block diagram of ammonia condensation system ..................................................... 3 5 4.1 Temperature-dependence ofconductivity for Li-NH3 ofconcentration 20 MPM ... 44 4.2 Temperature-dependence ofconductivity for Li-NH3 ofconcentration 10 MPM .... 45 4.3 Temperature-dependence ofconductivity for Li-NH3 ofconcentration 5 MPM ...... 46 4.4 Dependence ofrslao upon Li concentration ............................................................... 50 IV LIST OF TABLES 4.1 Free electron densities for lithium-ammonia solutions .......................................... 49 4.2 Dependence of freemean path upon concentration of solution at 21 OK .............. 53 V I. INTRODUCTION Background and History of Metal-Ammonia Solutions Because of their low electronic density, metal-ammonia solutions represent good systems to test theories of electron interaction in metals. The concentration of solution can be changed at will by changing the amount of metal added which makes possible the study of electrical conductivity and properties of electron transport under different conditions. In the past electron transport were done to provide insight into phase transition and possible superconducting behavior. Metal-ammonia solutions were discovered by Sir Humphrey Davy around 1808, when he made his first observation on bronze potassium ammonia [1]. In the same year, Seebeck prepared solutions ofNH4 in mercury, which he called "ammonium amalgams" and it was established that the dissolved species was N� [2]. In 1864, Weyl reported experiments in which it was observed that certain metals (sodium and potassium) dissolved in ammonia and he concluded that "metal­ ammoniums" (N�) were formed [3]. He suggested the existence of these components in which one or more hydrogen atoms was replaced with metal atoms. Weyl claimed in his paper [4] that it would be possible to prepare metal-ammonium MNH4 solutions by direct combination of ammonia and a highly electropositive metal. Around 1870, Seely repeated the work of Weyl and extended it to lithium and rubidium. He was the firstto consider the metal-ammonia solutions to be true solutions of metals in a solvent rather than compounds of metal and ammonia. Seely stated that alkali metals dissolve in ammonia as salts dissolve in water: "the solid disappears in the liquid and on evaporating the liquid, the solid reappears in its original form" [5]. Seely concluded that the liquid anhydrous ammonia is a solvent ofalkali metals and the metals did not react with the solvent and thereforeNH.i + (ammonium) did not form. A major contribution in the investigation and study ofthe metal ammonia solutions was made by Kraus. Kraus systematically studied the equilibrium vapor pressure ofammonia to determine the compositions ofphases fordifferent metal­ ammonia systems [6]. He studied solutions oflithium, sodium and potassium in ammonia. Kraus studied the change fromelectrolytic to metallic properties for metal ammonia systems and concluded in 1908 that the valence electron ofthe metal associates with the solvent in dilute solutions. The electron is surrounded by "an envelope ofsolvent molecules" and that the valence electron is freein concentrated solutions [7]. Kraus' work on sodium dissolved in ammonia stated that in dilute solutions the metal
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