Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2000 Experimental and theoretical investigations in alkaline earth-zinc-aluminum intermetallic systems Chi-Shen Lee Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Inorganic Chemistry Commons Recommended Citation Lee, Chi-Shen, "Experimental and theoretical investigations in alkaline earth-zinc-aluminum intermetallic systems " (2000). Retrospective Theses and Dissertations. 12696. https://lib.dr.iastate.edu/rtd/12696 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. For more information, please contact [email protected]. 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This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Art)or, Ml 48106-1346 ii Graduate College Iowa State University This is to certify that the Doctoral dissertation of Chi-Shen Lee has met the dissertation requirements of Iowa State University Signature was redacted for privacy. Major Professor Signature was redacted for privacy. le Major Program Signature was redacted for privacy. For the Create (college iii -Mm mh mm ''The action of Heaven is strong and dynamic. In the same manner, the noble man never ceases to strengthen himself.** - 1-Ching, Qian (No. I), Commentary on the images (Translated by Richard John Lynn) to my parents iv TABLE OF CONTENTS CHAPTER 1: GENERAL INTRODUCTION I Dissertation Organization 7 References 8 CHAPTER 2: EXPERIMENTAL .\ND THEORETICAL STUDIES OF BaZnioA!;: A NaZnn-TYPE INTERMETALLIC COMPOUND 10 Abstract 10 References 16 Supplementaiy Material 26 CHAPTER 3: WHERE ARE THE ELEMENTS IN COMPLEX ALUMINIDES? AN EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE QUASICRYSTALLINE APPROXIMANTS, Mg2-Y(ZnxAI,.x)3*Y 31 Abstract 31 Introduction 32 Experimental 35 Results and Discussion 42 R-Phase Mg-Zn-Al: Where Arc The Atoms? 53 Conclusions 54 References 56 Supplementary Material 81 CHAPTER 4: EXPERIMENTAL AND THEORETICAL STUDIES OF R-PHASE COMPOUNDS IN Li-Mg-Zn-AI SYSTEMS 95 Abstract 95 Introduction 96 The Theoretical Model 98 Experimental Studies of Quaternary Li-Mg-Zn-AI R-Phases 102 Results and Discussion 105 Conclusions 108 References 109 Supplementary Material 124 V CHAPTER 5; SITE-PREFERENCE STUDY OF TERNARY ALKALINE EARTH- ZINC ALUMINIDES SYSTEM FORMING STRUCTURAL VARIANTS OF BaAU 144 Abstract 144 Introduction 144 Experimental 146 Results 148 Discussion 151 Conclusion 155 References 155 CHAPTER 6: Bai4Zn5Al22: A NEW TERNARY INTERMETALLIC COMPOUND WITH A NOVEL 2D NETWORK 171 Abstract 171 Introduction 171 Experimental 172 Results and Discussion 178 Conclusion 184 References 184 CHAPTER 7: GENERAL CONCLUSIONS 206 APPENDIX A. REACTION COMPOSITION AND PRODUCT IDENTIFICATION 210 APPENDIX B. SUMMARY OF SINGLE CRYSTAL REFINEMENTS ON VARIOUS REACTIONS 213 APPENDIX C. ELECTRONIC STRUCTURE STUDIES OF BajPdPs AND RELATED COMPOUNDS 222 ACKNOWLEDGMENTS 251 1 CHAPTER 1 GENERAL INTRODUCTION Understanding the structure and property relationships of intermetallic compounds has been a goal of solid state chemists for decades.'"^ A great deal of synthetic effort has resulted in many new compounds with known or novel structure types/ Significant achievements in models for predicting structural features and properties of intermetallic compounds have been developed.' " One of the thoroughly studied systems is the Hume- Rothery phases. These compounds are made up of late transition metals (groups 8-12) through the post-transition metals, and their structural types can be predicted by their average valence electron concentration per atom (vec) between 1.0 and 2.0 e"/atom.' For example. In Ali-xCux system, the vec of AI2CU3 (e-brass) is (2x3+3x1 )/5 = 1.8 (d electrons of Cu are excluded) and the structure type of AI2CU3 adopts the hexagonal close-pack (h.c.p.) structure (see Figure la). On the other hand, the P-brass (Ali-xCu*, x = 0.70~0.82, vec = 1.36 ~1.6) adopts the body centered cubic (b.c.c.) structure type. Another example is Wade's rule that relates the structure of molecular cluster (e.g. borane clusters) with its "magic" electron count.^ During the last decade, theoretical calculations have been extensively used to understand the electronic structures of solid state compounds.^ '^ One of the contributions was the application of the second-moment scaling to sort the relative stability of elements in different structure types." The concept of the valence electron concentration per atom (vec) has been applied to identify structure types of Hume-Rothery phases and may be used as an index to group intermetallic compounds. The vec can be calculated in two ways: 2 a) e"/atom: The vec is calculated as the total number of valence electron divided by the number of atoms per formula. This definition includes every atom in the formula and was used in the Hume-Rothery phases. This counting scheme was applied to the Mg-Zn-Al system because of the similar electronegativities for Mg(l.31), Zn (1.65), and A1 (1.61). b) e"/e!ectronegative atom: The vec is calculated as the total number of valence electron per formula divided by the number of electronegative atoms per formula. This definition was used in ZintI phases because such compounds contain electropositive elements (e.g. alkali/alkaline earth metals). The electropositive elements are treated as electron donor and the vec does not include the contribution of such metal. For example, in the BaZn^AU.^ (0 < X < 2), the vec range is between 3.0 (BaZn2Al2, vec = (2 + 2x2 + 2x3)/4 = 3.0) and 3.5 (BaAU) e7anions. Three possible groups of intermetallic compounds can be categorized by different vec ranges and they are discussed below; 1) 1.0 < vec < 2.0: Hume-Rothery phases represent compounds with such a vec range. As mentioned before, the structure types (e.g., h.c.p. or c.c.p.) of Hume-Rothery phases depend on the vec range. Their structures are more complex than corresponding elementals and their packing efficiencies are usually higher than that of the metal elements themselves due to different atomic sizes. The composition of Hume-Rothery phases is flexible resulting in phase widths. For example, the c-brass phase (h.c.p.) is between 56 and 60 atom% Cu in AluxCUx binary system. 2) vec ^ 4.0: Zint! phases stand for the intermetallic compounds in such vec range. The Zintl phases usually contain two kinds of metals: one is an electropositive metal (i.e.. 3 group 1 or 2 element) and the other is a main group element from group IB-ie.'"* To calculate the vec for ZintI compound, the electropositive metal is treated as an electron donor and the vec is calculated by the total number of valence electrons (per formula) divided by the number of main group metal atoms. For example, the vec of LiAl is equal to (1 + 3)/l = 4.0. According to the Zintl-Klemm concept, the main- group element is reduced by the electropositive metal and the electronic configuration of the reduced atom fulfills the octet rule. Therefore, Al is reduced by Li and the ionic substructure of j [Af] is equivalent to the diamond network because Al" has the same number of valence electrons as C (see Figure Ib).'^ Since each atom from the ionic network comply with the octet rule, the Zintl compounds are electron precise with fixed compositions. .Al Li (a) AI2CU3 (b) LiAl Figure 1. The structures of AI2CU3 (a) and LiAl (b) 4 3) 2.0 < vec < 4.0 : The structure types of compounds with this vec range are more complex than Hume-Rothery and Zintl phases, and classification of their relationship between vec and structure types is difficult. For example, the NaZn^-type phase exists in the ternary Ba-Cu-Al and Ba-Zn-Al systems.