ELECTROSYNTHESIS AND CHARACTERIZATION OF MAIN GROUP AND TRANSITION METAL OXIDES by TU NGOC NGUYEN B.S., University of California, Berkeley (December 1988) Submitted to the Department of Chemistry in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May 1994 © Massachusetts Institute of Technology, 1994 All rights reserved Signature of Author. Department of Chemistry ,, .1 May 6, 1994 Certified by A/ I - uw Hans-Conrad zur Loye Thesis Supervisor Accepted by . -, ! Glenn A. Berchtold Chairman,-. Departmental Committee on Graduate Students JUN 2 1 1994) 2 This doctoral thesis has been examined by a Committee of the Department of Chemistry as follows: , . HE [ // Professor Dietmar Seyferth. / Chairii e"'" ! Professor Hans-Conrad zur Love___ Thesis Supervisor 62 Professor Alan Davison - - - 3 ELECTROSYNTHESIS AND CHARACTERIZATION OF MAIN GROUP AND TRANSITION METAL OXIDES by Tu Ngoc Nguyen Submitted to the Department of Chemistry, May 6, 1994, in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Chemistry ABSTRACT Chapter 1: General Introduction A brief review of solid state synthetic techniques is given. The research discussed in this thesis is introduced. Chapter 2: Electrosynthesis of Highly Oxidized Transition Metal and Main Group Oxides in Molten Hydroxides The development of electrosynthesis in molten hydroxides of oxides containing high valent transition metals and main group metals is described. Electrosynthesis is shown to be a viable route to such materials, including, KBiO 3, NaNiO2, NaxCoO2, Srl.75CuO5.13, NaBa2Cu3O5, Ca4PtO6, and Sr3NiPtO6. Experimental are discussed. 5 The ionic conductivity of KBiO3 was determined to be 10- S/cm at 300 °C, about 3 orders of magnitude lower than the conducitivity of the analogous NaSbO3o1/6NaF. The + low conductivity of KBiO 3 was explained by the high size ratio of K to BiS+ compared to Na+ and Sb 5+, the low mobility of K+ compared to that of Na+, and the role of the K+ ion in stalilizing the Bi-O framework structure. Chapter 3: Structural and Magnetic Characterization of the One-Dimensional Oxides, Sr3MPtO 6, M = Co, Ni, Cu, Zn The synthesis and characterization of a family of one-dimensional oxides, Sr3MPtO6, M = Co, Ni, Cu, Zn, is described. The structure was determined using Rietveld analysis of powder X-ray and neutron diffraction data. Sr3MPtO6 contains infinite chains composed of alternating, face-sharing PtO6 octahedra and M06 trigonal prisms. Sr3ZnPtO6 is diamagnetic. Sr3CuPtO6 displays well-behaved linear chain Heisenberg antiferromagnetism, with IJI/k = 26.1 K and g = 2.21. Sr3NiPtO6, a S = 1 system, shows an onset of low-dimensional antiferromagnetism at -25 K, with no long- 4 range ordering as determined by powder neutron diffraction. Sr3CoPtO6 displays unprecedented random spin paramagnetism with spin disorder along the chains. The magnetic coupling in this material is between ferromagnetically-ordered chain segments to give an averaged total singlet ground state. Chapter 4: Structural and Magnetic Characterization of the One-Dimensional Oxides, Sr3MIrO 6 , M = Ni, Cu, Zn A family of one-dimensional oxides, Sr3MIrO6, M = Ni, Cu, Zn, analogous to the platinum-containing oxides discussed in Chapter 4, has been structurally and magnetically characterized. The structure was determined using Rietveld analysis of powder X-ray and neutron diffraction data and found to be isostructural to Sr3NiPtO6. Sr3ZnrO6, a S = 1/2 system, displays antiferromagnetic behavior that could be fitted an alternating chain model. Sr3CuIrO6 shows ferromagnetic behavior with a saturation magnetization of -0.6 LgB/mol.Finally, Sr3NilrO6 exhibits complex magnetic behavior indicative of intrachain ferromagnetism and interchain antiferromagnetism to give a singlet ground state at low temperatures. Chapter 5: Designing A One-Dimensional Random Spin System: Characterization of the Solid Solution Sr 3CuPt 1xlrxO6 (0 x a 1) The solid solution Sr3CuPt1.xlrxO6 (0 < x < 1) was prepared and characterized to study random spin paramagnetism. The solid solution exhibited magnetic behavior in agreement with the theoretically predicted random spin paramagnetic behavior. One composition in particular, Sr3CuPto.5Ir0.506, shows the expected magnetic and high temperature heat capacity characteristics of random spin paramagnetism. Thesis Supervisor: Dr. Hans-Conrad zur Loye Title: Paul M. Cook Career Development Professor of Chemistry 5 TABLE OF CONTENTS Title Page ................................................. 1 Signature Page ....................................................................................................................2 Abstract .................. .............................................................................................................3 Table of Contents ................................................. 5............................................................... List of Figures .....................................................................................................................8 List of Tables ............................................................................................................. 11 List of Schemes ................................................. 12 Dedication ................................................. 13 Acknowledgements ...........................................................................................................14 Chapter 1: General Introduction ..................................................................................15 References.................................................. 21 Chapter 2: Electrosynthesis of Highly Oxidized Transition Metal and Main Group Oxides in Molten Hydroxides ..................................... 23 Introduction ..........................................................................................................24 Experimental ........................................................................................................ 28 Synthesis of KBiO3 ................................................. 29 Synthesis of NaNiO2 ................................................. 31 Synthesis of NaxCoO2 ................................................................................ 31 Synthesis of Sr .75Cu30 5.13........................................................................ 32 Synthesis of NaBa2Cu305 ........................................ 32 Synthesis of Sr3NiPtO6 ............................................................................... 32 Synthesis of Ca4PtO6 .................................................................................. 33 Characterization of KBiO3 ................................................. 34 Results and Discussion ................................................. 45 6 Conclusions ..........................................................................................................51 References ............................................................................................................52 Chapter 3: Structural and Magnetic Characterization of the One-Dimensional Oxides, Sr3MPtO 6 where M = Co, Ni, Cu, Zn ......... 55 Introduction ........................................................ 56 Experimental .........................................................................................................57 Results and Discussion ......................................................... 59 Characterization of Sr3CuPtO6.................................................................... 59 Characterization of Sr3NiPtO6..................................................................... 63 Characterization of Sr3CoPtO6.................................................................... 74 Characterization of Sr3ZnPtO6 ....................................................................89 Trends in the Magnetic Data ........................................ ................ 89 Conclusions ........................................................ 94 References......................................................... 95 Chapter 4: Structural and Magnetic Characterization of the One-Dimensional Oxides, Sr3MlrO 6 where M = Ni, Cu, Zn ................ 97 Introduction......................................................... 98 Experimental .........................................................................................................98 Results and Discussion ......................................................... 100 Characterization of Sr3ZnrO6 ........................................................ 100 Characterization of Sr3CuIO6 ......................................................... 107 Characterization of Sr3NiIrO6 ........................................ ................ 113 Trends in the Magnetic Data ........................................................ 126 Conclusions ........................................................ 127 References ...........................................................................................................128 7 Chapter 5: Designing A One-Dimensional Random Spin System: Characterization of the Solid Solution Sr 3CuPt 1.xIrxO6 (0 < x < 1) ... 129 Introduction .........................................................................................................130 Results and Discussion ........................................ 133 Conclusions .........................................................................................................139