Maarten C. Verbraeken Phd Thesis
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DOPED ALKALINE EARTH (NITRIDE) HYDRIDES Maarten Christiaan Verbraeken A Thesis Submitted for the Degree of PhD at the University of St. Andrews 2009 Full metadata for this item is available in the St Andrews Digital Research Repository at: https://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/714 This item is protected by original copyright Doped alkaline earth (nitride) hydrides A thesis presented for the degree of Doctor of Philosophy by Maarten Christiaan Verbraeken University of St Andrews Supervised by Prof. J.T.S. Irvine Submitted February 2009 Doped alkaline earth (nitride) hydrides Declarations I, Maarten Christiaan Verbraeken, hereby certify that this thesis, which is approximately 40,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. I was admitted as a research student in June 2005 and as a candidate for the degree of Doctor of Philosophy in November 2006; the higher study for which this is a record was carried out in the University of St Andrews between 2005 and 2009. Date:……………….. Signature of candidate:………………………….. I hereby certify that the candidate has fulfilled the conditions of the Resolution and Regulations appropriate for the degree of Doctor of Philosophy in the University of St Andrews and that the candidate is qualified to submit this thesis in application for that degree. Date:……………….. Signature of supervisor:…………………………. In submitting this thesis to the University of St Andrews we understand that we are giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being affected thereby. We also understand that the title and the abstract will be published, and that a copy of the work may be made and supplied to any bona fide library or research worker, that my thesis will be electronically accessible for personal or research use unless exempt by award of an embargo as requested below, and that the library has the right to migrate my thesis into new electronic forms as required to ensure continued access to the thesis. We have obtained any third-party copyright permissions that may be required in order to allow such access and migration, or have requested the appropriate embargo below. Access to Printed copy and electronic publication of thesis through the University of St Andrews. Date:…………………. Signature of candidate:………………………….. Signature of supervisor:…………………………. iii Doped alkaline earth (nitride) hydrides Summary The work in this thesis relates to the preparation and structural and electrical characterisation of calcium and strontium hydrides, imides and nitride hydrides. Conventional solid state methods in controlled atmospheres were used to synthesise these materials. High temperature neutron diffraction, thermal analysis and conductivity studies performed on calcium and strontium hydride suggest an order – disorder transition in these materials at 350 – 450°C. Disordering is believed to involve rapid exchange of hydride ions across two crystallographic sites. This manifests itself in a lowering of the activation energy for bulk hydride ion conduction. The hydride ion conduction is good in these undoped materials: σtotal = 0.01 S/cm for CaH2 at 1000K; for SrH2, σtotal = 0.01 S/cm at 830K. Doping of SrH2 with NaH causes a significant increase in the low temperature conductivity, due to presence of extrinsic defects. The high temperature conductivity is negatively affected by NaH doping. Calcium nitride hydride (Ca2NH) was obtained as a single phase material by reacting either calcium metal or calcium hydride (CaH2) in an argon atmosphere containing 5 – 7% H2 and 1 – 7% N2. Imide ions substituting for hydride and nitride ions constitute a major chemical defect in this material. Long range ordering of the nitride and hydride ions occurs, giving rise to a double cubic crystal symmetry. This order breaks down at 600 – 650°C. Applying the same reaction conditions to strontium metal results in a mixed phase of strontium nitride hydride and imide. No long range order in the nitride hydride phase could be observed. Doping Ca2NH with lithium hydride (LiH) causes the appearance of a second calcium imide phase, whereas doping with sodium hydride (NaH) increases the amount of imide ions as a defect in the nitride hydride structure, thereby decreasing the long range ordering of nitride and hydride ions. iv Doped alkaline earth (nitride) hydrides Acknowledgements First of all, I would like to thank Prof. John Irvine for offering me the PhD position in his group on this project. My experience in the field of solid state chemistry prior to this PhD was quite minimal and so was the knowledge and experience within the group on this specific type of chemistry I have been doing, so all your scientific input and support have been ever so helpful in getting this work done. Also your positivism about the usefulness of hydride ion electrochemistry (which possibly not everybody shares) has absolutely been an inspiration. Thanks also go to the members of the JTSI group, who I’ve worked with over the past three and a half years. I’d like to especially thank Julie for all the help in the lab, the moral support during glovebox maintenance operations and just everything. Thank you, Sylvia, for always finding slots for me on the thermal analysis equipment and for getting me hooked on Lost. I’d also like to thank the people from the David-Cole Hamilton group for allowing me to use some of their lab space and helping me prepare some chemicals; especially thanks to Simon for spending hours with me trying to prepare sodium hydride (we never managed to do it, but it was fun playing with all those explosive chemicals!!). Big thanks too, to Bobby, George, Jim, Brian and Colin for fixing all sorts of things in your workshops and also for helping me move that glovebox a few times. I couldn’t have done this work without your help, guys. The final work related thanks are for Institut Laue Langevin (ILL) in Grenoble, France, for granting me beamtime on their neutron beamline and to Emmanuelle Suard in particular for helping me carrying out my experiments there. Then there is of course the words of gratitude to the people who helped me get through three and a half years outside the chemistry building. Cheers, Fran and Kelcey for initiating me in the Cellar Bar music quiz, which we’ve managed to win all of once during my stay here. Thanks Davo for bringing Australian drinking culture to St Andrews and for bringing the thunder on many occasions; Chris, Dave, Steve, Maria, Walter and Davo (again) for putting up with me in the house and for all the banter and shenanigans….and for some reason I can see some more coming up in the near future; Gil for some excellent cooking and some infamous parties; Sneh for endless positive energy and Pierrot for being Pierrot; Mark and Diane for great company and being brilliant beer connoisseurs. Finally a big thank to the jazz gang in the Byre for keeping the groove going on Thursdays and any other gigs. Switching to Dutch: Bedankt, Pa en Ma voor jullie continue morele en financiele steun de afgelopen jaren. Ik weet dat ik gedurende een lange periode het niet al te zonnig inzag, maar gelukkig kon ik altijd op jullie positieve kijk en vertrouwen rekenen. En nu is het dan toch eindelijk zover: het boekje is klaar! v Doped alkaline earth (nitride) hydrides Contents 1 Introduction............................................................................................................................. 1 1.1 Hydrogen chemistry........................................................................................................ 4 1.1.1 Hydrogen – the element .......................................................................................... 4 1.1.2 Hydrogen and its ions.............................................................................................. 4 1.1.3 Hydrogen compounds ............................................................................................. 5 - 1.1.4 The H /H2 equilibrium – the hydrides ....................................................................... 6 1.2 Crystal structures of hydrides ......................................................................................... 8 1.3 Thermodynamics of metal hydrides.............................................................................. 10 1.4 Saline hydrides ............................................................................................................. 12 1.5 Metallic hydrides ........................................................................................................... 13 1.5.1 Bonding in metallic hydrides.................................................................................. 13 1.5.2 Electrical properties of metallic hydrides ............................................................... 14 1.6 Nitride, nitride hydride and imide chemistry of the group I and II elements.................. 16 1.6.1 Lithium nitride, α-Li3N ............................................................................................ 16 1.6.2 Nitrides of the heavier alkali metals....................................................................... 17 1.6.3 Calcium nitrides ....................................................................................................