Polar Intermetallic Compounds of the Silicon and Arsenic Family Elements
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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1996 Polar intermetallic compounds of the silicon and arsenic family elements and their ternary hydrides and fluorides Efigenio Alejandro León-Escamilla Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Inorganic Chemistry Commons Recommended Citation León-Escamilla, Efigenio Alejandro, "Polar intermetallic compounds of the silicon and arsenic family elements and their ternary hydrides and fluorides " (1996). Retrospective Theses and Dissertations. 11547. https://lib.dr.iastate.edu/rtd/11547 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. 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UMI A Bell & Howell Information Company 300 North Zed) Road, Ann Arbor MI 48106-1346 USA 313/761-4700 800/521-0600 Polar interinetallic compounds of the silicon and arsenic temily elements and their ternary hydrides and fluorides by Efigenio Alejandro Le6n-Escamilla A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Inorganic Chemistry Major Professor: John D. Corbett Iowa State University Ames, Iowa 1996 DMI Number: 9712575 UMI Microform 9712575 Copyright 1997, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 ii Graduate College Iowa State University This is to certify that the doctoral dissertation of Efigenio Alejandro Le6n-Escamilla has met the dissertation requirements of Iowa State University Signature was redacted for privacy. MalorMajor Professor Signature was redacted for privacy. For the Major Program Signature was redacted for privacy. For tl^G^muate College iii TABLE OF CONTENTS CHAPTER I. GENERAL INTRODUCTION 1 CHAPTER II. EXPERIMENTAL 4 Materials 4 Source 4 Handling 4 Containers 4 Dehydrogenation of Metals 6 Preparation of Metal Fluorides (MFj) 7 Preparation of Binary Metal Hydrides (MHJ 7 Preparation of Binary and Ternary Intermetallic Compounds 8 Reactions in presence of hydrogen or in sealed SiOj containers (sc) 8 Reactions in absence of hydrogen or under dynamic vacuum (dv) 9 Preparation of Ternary Deuterides 10 Furnaces 10 Characterization Techniques 11 identification of Products and Lattice Parameters Calculation 11 Single Crystal X-Ray Work 12 Powder Neutron Diffraction 13 Electrical Resistivity Measurements 15 Magnetic Susceptibility Measurements 16 Theoretical Calculations 16 CHAPTER III. PNICTIDE SYSTEMS 18 AgPngH^ Systems 18 Introduction 18 Results and Discussion 23 BasSbgH, 23 CagSbgH, 35 YbjSbjH^ and SrsBigH^ 47 iv CasBiaH, 53 Other AjPnaH, systems 58 Electrical resistivity and magnetic properties 84 Trivalent rare-earth-metal pnictides 101 Arsenides 104 Antimonides 105 Bismuthides 117 Interpretation of results 118 Conclusions About the A5Pn3(H,F), Systems 119 AigPn,, Systems 129 Introduction 129 Results and Discussion 136 Ca,sSb„ 136 Other A,gPn,, systems 150 Magnetic properties 154 Conclusions About the AigPn,, Systems 157 CHAPTER IV. TETRELIDE AND TRIELIDE SYSTEMS 162 AgTtaH^ and AgTrgHj, Systems 162 Introduction 162 Results and Discussion 168 CajSnaCH.D.F)^ systems 168 Other A5Tt3(H,F)^ systems 178 Silicides 180 Germanides 201 Stannides 210 Plumbides 211 Trielides (AjTrgH,) 218 Electrical resistivity and magnetic properties 228 YbagSnja System 240 Conclusions About the Tretrelide and Trielide Systems 256 V CHAPTER V. SUMMARY AND FUTURE WORK 262 APPENDIX A. Ca^Sbg,, 265 APPENDIX B. DISTORTED Ca^eBIn 270 APPENDIX C. Sr36Sb24Z 273 BIBLIOGRAPHY 281 ACKNOWLEDGEMENTS 290 1 CHAPTER I. GENERAL INTRODUCTION Our ability to understand, and possibly to predict, the properties of intennetallic compounds on the basis of their structural Information is many times limited by uncertainties about their correct compositions. The unsuspected presence of adventitious impurities in a compound may lead one to draw inaccurate, or equivocal, conclusions about their unexplained behaviors. The occurrence of such situations in the published literature has been quite frequent. For instance, the inadvertent presence of hydrogen impurities in what was thought to be pure calcium prompted Smith and Bernstein^ to assign a hexagonal allotropic form to calcium. Subsequent investigation by Peterson and Fattore^ showed the hexagonal phase was an Intermediate in the binary calcium-hydrogen system. In similar circumstances, an hexagonal allotrope of ytterbium metal was later established as an ytterbium hydride compound.^ Adventitious impurities in an intermetallic compound may stabilize a phase in a particular stnjcture that would otherwise not form in the binary system. Such stabilization processes are probably electronically driven. Examples in literature of impurity-stabilized compounds are vast. Thus, many of the so-called Nowotny phases are, or were thought to be, compounds stabilized by non-metallic impurities."® The presence and stabilizing effects of impurities were not recognized until higher quality reagents and more accurate and thoughtful experimental techniques were available, and there was need to reconsider conflictive information already reported. As an illustration, arguments of dimorphism between a hexagonal and a tetragonal structure for LagSng were clarified by Kwon and Corbett.® They demonstrated that the hexagonal phase was an oxygen- stabilized compound, LagSnaO. The structures of intermetallic compounds formed by the combinations of pre- and post-transition elements can frequently be rationalized by the ZintI prindples from the chemist's point of view. Schafer and coworkers^-® ® have particularly demonstrated that a great many favorable combinations of structures and compositions can be classified as Zinti phases. The ZintI concept,'" in a very simple way, is based on the assumption that the electropositive element, of say a binary phase A^B^, transfers all Its electrons to the electronegative element (B) which uses these extra electrons to form 2 covalent bonds (B-B), i.e., two-center two-electron bonds and localized nonbonding pairs. It is believed that the elements tend to do this in order to achieve closed shell configurations. The apparent closed shell configurations of ZintI phases suggest their properties should be those of semiconductive and diamagnetic compounds. It is remarkable how a set of simple pnnciples enables us to repeatedly predict the electronic and magnetic properties of numerous intermetallic compounds. Recently, however, it has been found that several compounds that structurally qualify as Zinti phases are metallic conductors."'^^ Arguments of weak cation-anion and cation-cation electronic Interactions had been invoked to explain such unexpected behavlor.'^-^* '® Studies on tiie stabilizing effect of interstitial hydrogen in intemnetallics are sparse. Most of these studies has been directed to understanding the dynamics of hydrogen absorption and have been encouraged by the potential of the materials for hydrogen storage and hydrogen pumps.^® '' '® Additionally, most of the experiments in this area have been limited to the lanthanide elements. Hydrogen, a common and sizable impurity in alkaline-earth metals,^^ has been repeatedly ignored as far as its participation in reactions with the latter metals. Presumption of its "inactive spectator" role is, many times, equivocal. Suspicions about the involvement of hydrogen in the solid state chemistry of the alkaline-earth and divalent rare-earth metal pnictides originated after ambiguities between experimental evidence obtained in this laboratory and previous literature reports were found. In an attempt to clarify several ambiguities from previous reports, we have through careful and purposeful work Investigated the interstitial-stabilizing influence of hydrogen In the alkaline-earth