Thesis (D.Sc. (Chemistry)) - Rhodes University, 2006. / [Appendix]. Dedication - Acknowledgements - Curriculum vitae - Biographical notes - Publication list - Introduction to my research - Commentary-books - Commentary-research papers - Conclusions.

I have chosen the title for this thesis, "Reactions in the Solid State", for two reasons: Firstly, it is broad enough to cover all of my areas of research, which have been: • Effects of irradiation on solids (PhD topic) • Silver refining (while at the Chamber of Mines) • Kinetics of decomposition of solids (with Dr A.K. Galwey and various others) • Techniques of thermal analysis • Pyrotechnic delay systems (with support from AECI Explosives) • Thermal and photostability of drugs (with Prof B.D. Glass) and, secondly, it was the title of the very successful book co-authored by Drs Andrew Galwey, David Dollimore and me. A large part of my research has been involved in the writing and editing of books, so these are covered in a separate commentary, while commentary on the more than 100 papers to which I have contributed forms the main part of this compilation. It is hoped that the electronic format will enable ready access of to all aspects of my research, including electronic versions of the original papers. The reader will need a copy of Adobe Acrobat Reader to access these.

Thesis (MTech (Science))--Peninsula Technikon, Cape Town, 1998 / The chemical system, Si < >1 Pd 1Cr, was investigated to study the formation of CrSil on polycrystalline PdlSi, formed on Si<IOO> and epitaxial PdlSi formed on Si<lll>. To ascertain the reaction mechanism during the formation, tantalum was used as an inert marker, since it does not participate in the reaction and is readily measured by Rutherford Backscattering Spectrometry (RBS). This investigation was performed in two parts. In the first part, the tantalum was inserted in the PdlSi layer to determine which species; palladium or silicon diffuses during CrSil formation. In the second part, the marker was inserted in the CrSiI layer to determine whether chromium or silicon moves. In addition, the effect of marker thickness on the growth of CrSiI was investigated. The samples were prepared by electron gun evaporation in vacuum, the elements being deposited on the particular silicon substrates. This was followed by the thermal treatment of the samples at temperatures of 400,425,450,475,500 and 550°C. Normal and dynamic Rutherford backscattering spectrometry was used to characterize the thin film structures. If the marker, when inserted in the PdISi layer, should move towards the PdISi I CrSil interface then, the formation of CrSil would be due to the dissociation of Pd2Si. In this case PdlSi dissociates into Pd and Si and the Si diffuses to the interface of CrSi2 and Cr to form CrSil, whereas the Pd diffuses to the Si < > I Pd2Si interface to regrow PdISi. However, if the marker position remains constant with respect to the Pd2Si layer it can be concluded that the formation of CrSiI is due to the movement of Si from the substrate to the interface of CrSi2 and Cr to form CrSiI. If the marker when inserted in the CrSi2 should move towards the sample surface then the chromium diffuses to the interface ofCrSi1 and PdlSi to react with the silicon, forming CrSi2 .

Metal chalcogenides are one of the most important class of compounds in the field of Inorganic Chemistry. A wide variety of chalco-anion building blocks provides excellent opportunities to synthesize new compounds with unique structure and properties, essential drives in maximizing technological impact. In this dissertation, the exploratory synthesis of new mixed-metal chalcogenide compounds is carried out. The novel phases were characterized using a wide spectrum of techniques, and their properties were investigated. The project started by investigating the synthesis of zeolite-like chalcogenides using a solid-state reaction. As a result, the thioaluminogermanate Na(AlS2)(GeS2)4 was synthesized with successful insertion of Al3+ cations into the chalcogenogermanate framework. This effectively extended the structural chemistry for this family of materials and approximated them to the aluminosilicate zeolites. The crystal structure of Na(AlS2)(GeS2)4 displayed a [(AlS2)(GeS2)4]1- 3D polyanionic framework, in which Al and Ge atoms share atomic positions and Na cations occupy the channels in-between. At room temperature and in a solvent medium, this compound exhibits a unique cation-exchange property with monovalent Ag+ and Cu+ ions, resulting in the formation of the isostructural compounds Ag(AlS2)(GeS2)4 and Cu(AlS2)(GeS2)4. The replacement of Na+ in the parent compound with Ag+ or Cu+ results in enhanced properties such as higher stability in air and narrower bandgap energies. The completeness of the ion-exchange reactions was confirmed using various analytical tools including single crystal XRD, EDX, and 23Na NMR. Following this initial success, a systematic study was carried out to synthesize unknown phases of transition and main group mixed-metal chalcogenides. As a result, the first example of an alkali/transition metal thioaluminate compound K2Cu3AlS4 was synthesized. For this, a solid-state reaction with K2S acting as a self-flux was used. The crystal structure of K2Cu3AlS4 consists of [Cu3AlS4]2- polyanionic anti-PbO type layers, in which Al and Cu atoms share the atomic positions, separated by K+ cations. The coordination environments of the Al and K cations were confirmed by solid-state 27Al and 39K NMR spectroscopies. The optical property and thermal stability of this new quaternary compound were also studied. The mixed-metal chalcogenides class is not restricted only to purely inorganic components; it can also be extended to inorganic-organic hybrid materials. In an attempt to synthesize main group chalcogenides mixed with transition metal complexes, the new compound [Ni(en)3]GeS2(OH)2•H2O was obtained. In the complex cation [Ni(en)3]2+, the ethylenediamine (en) ligands are bidentate to the Ni2+ through the N atoms resulting in a distorted octahedral geometry which is charge balanced by the rarely observed [GeS2(OH)2]2- tetrahedral anion. In agreement with single crystal data, the solid-state 1H NMR spectrum exhibits four signals corresponding to the -CH2 and NH2 protons of the (en) in addition to the H2O and -OH protons. This compound exhibits a paramagnetic response, studied by EPR spectroscopy and ZFC/FC magnetization measurements. The optical properties including UV-Vis absorption and photoluminescence emission were also measured. Knowing that it was possible to synthesize various types of mixed-metal chalcogenides, the focus was shifted to the production of those with interesting functional properties. In this way, Na2BiSbQ4 (Q = S, Se, Te) compounds were synthesized by reacting Bi and Sb in the corresponding Na2Q flux. The three phases obtained are isostructural and crystallize with NaCl-type structure. The unique feature of these structures is the existence of only one crystallographic metal site in the unit cell (where Bi, Sb and Na share the same atomic position). These mix of position sites provide the desirable lattice complexity with a totally random distribution of Na, Bi and Sb atoms. As expected, extremely low thermal conductivities at room temperature have been observed for the studied phases. The optical properties, solid-state 27Na NMR spectra, chemical and thermal stabilities are discussed.

No description available.

This dissertation is dedicated to investigating the thermoelectric properties of the Zn – Sb phases and particularly the Zn13Sb10 material, which was shown to achieve a high ZT (1.3 at 670K) in 1997. The Zn13Sb10 material (known as “Zn4Sb3”) was then extensively studied as a potential thermoelectric material. The Zn13Sb10 materials, however, were not widely adapted in thermoelectric applications. A new synthetic procedure was developed to synthesize phase-pure Zn13Sb10 materials in this thesis, thus allowing a robust characterization of the Zn13Sb10-based materials. This work aims to improve the thermoelectric performance of the Zn13Sb10- based materials by substituting foreign elements into the structure of the Zn13Sb10 phase, at the same time characterize and navigate the synthesis-property-composition relationship of the doped Zn13Sb10 materials. On the other hand, some relative Zn–Sb phases such as the α- and β-Zn3Sb2 were also studied in attempt to complete the characterizations of all Zn–Sb phases stable at room temperatures. The ZnSb phase, another well-studied Zn–Sb material, was investigated in coherence with the Zn13Sb10 materials to understand the effects to transport properties brought by the same atom replacement in the two systems. This was realized in the form of a comparison between the (Zn,Cd)Sb and (Zn,Cd)13Sb10 solid solution series. Materials studied in this work were mostly made using the melt and solidification method. Powder and single-crystal X-ray diffractions were employed to characterize samples’ purity and structure determination. Energy-dispersive X-ray Spectroscopy (EDS) was used to determine sample compositions, especially to confirm the presence(s) of dopants in materials in small quantities. Physical properties of materials were measured to evaluate the thermoelectric performances of materials. Computational methods, such as the linear muffin-tin orbital (LMTO) method was used to help understand the transport properties of materials and the electron localization function (ELF) method to analyze the bonding natures between atoms. / Thesis / Doctor of Philosophy (PhD) / Thermoelectric materials are incorporated into thermoelectric devices to generate electricity from heat sources. As there are environmental concerns and increasing demand of energy supplies in the society, thermoelectricity may relieve some of the pressure by waste heat recovery, from internal combustion engines for example. This work is dedicated to studying the zinc–antimony (Zn–Sb) materials and a focus on the Zn13Sb10 material for thermoelectric applications. This work aims to improve the thermoelectric efficiency of the Zn13Sb10 material, at the same time understand the changes on the physical properties brought by the structural and the compositional differences of the material. The relative Zn–Sb phases, such as ZnSb and Zn3Sb2, were also characterized to compare their structures with their physical properties.

No description available.

This thesis is concerned with a systematic study of phosphine-containing transition metal complexes and cluster compounds by high resolution solid state nmr spectroscopy, using the techniques of magic angle spinning and cross polarisation. Previous work has indicated the potential of the solid state nmr technique to investigate a variety of materials: this is considered in the introduction to this thesis, and the reasons for choosing to study transition metal phosphine compounds are discussed. The analysis of spinning sidebands to obtain the principle values of the shielding tensor is examined to determine how well the calculated values represent the true values. Simulations of slow MAS spectra are proposed as a means of testing and refining the calculated tensor components before attempting to correlate the shielding with structural parameters. The results of a study of a series of crystalline phosphine-containing complexes and clusters are presented. The spectra are interpreted on the basis of the known crystal structures: in some cases separate resonances can be resolved in the solid state spectra from the distinct phosphine environments of a cluster framework, and from inequivalent sites in the unit cell. Information is obtained from the isotropic shifts, scalar couplings and the chemical shift anisotropy. Many of the compounds are fluxional in solution, some even at low temperature: whereas a number of these are found to be rigid in the solid state at room temperature, some of the crystalline compounds retain their fluxionality. Investigations of the species formed when transition metal carbonyl clusters are anchored to oxide supports were carried out. These show the presence of several distinct phosphorus-containing species, some of which are not consistent with the simple attachment of the cluster to the surface. The unique importance of the solid state technique is demonstrated in the study of these supported species.

This investigation is based on the topochemical modification of three set of phases: Sr₃Co₂O₅Cl₂, SrO(Sr(Ru_0.5M_0.5)O₃)n (M = Ti, Mn, Fe; n = 1, 2, &infin;), and SrO(SrVO₃)n (n = 1, 2, &infin;). The topochemical reduction of Sr₃Co₂O₅Cl₂ using sodium hydride as a solid state reducing agent results in the formation of a reduced phase containing cobalt centres with an average oxidation state of +2 and an overall composition of Sr₃Co₂O₄Cl₂. The resulting material adopts a structure containing double sheets of square-planar corner-sharing CoO2 units separated by rock salt SrCl layers. Variable-temperature diffraction measurements reveal that these sheets undergo a cooperative Jahn-Teller distortion at T ~ 200 K due to unevenly filled degenerate (d_xy, d_yz) orbitals. This material adopts a magnetic structure in which the moments within each sheet are ordered antiferromagnetically, but the sheets are aligned ferromagnetically. An investigation was carried on the reduction behaviour of Ru-doped Sr(Ru_xFe_1-x)O₃. It was found that the reduction was non-topochemical for values of x > 0.5. For values of 0 < x < 0.5, no single phase precursor material could be formed. For the material with x = 0.5, reduction with CaH₂ produced a new phase with composition Sr(Ru_0.5Fe_0.5)O₂. This material is the first reported instance of Ru²⁺ in an extended transition metal oxide. DFT calculations reveal that, while the iron centres adopt a high-spin configuration, the ruthenium centres are in an intermediate-spin S = 1 configuration. Resulting competing magnetic interactions lead to frustration and lack of ordering. In order to further study the reduction behaviour of extended transition metal oxides containing ruthenium, the reduction of Sr₂(Ru_0.5Fe_0.5)O₄ and Sr₃(Ru_0.5Fe_0.5)₂O₇ was performed using CaH₂ as a solid state reducing agent. In these cases, reduction leads to segregation of the materials into multiple phases adopting closely related structures that differ mainly in their oxygen content. In these materials, the ruthenium centres are preferentially reduced, such that starting from materials containing Ru⁵⁺ and Fe³⁺, materials containing Ru^(3-δ)+ and Fe³⁺ are produced. Similarly, the low-temperature oxidation using CuF₂ as a solid state fluoride source was performed on materials with composition Sr3(Ru0.5M0.5)2O7 (M = Ti, Mn, Fe). In the case of M = Mn and Ti, materials with composition Sr₃(Ru_0.5Fe_0.5)₂O₇F₂ are produced in which the ruthenium centres are oxidised to Ru⁶⁺. For the M = Fe material, oxidation results in partial exchange of O for F and a material with composition Sr₃(Ru_0.5Fe_0.5)₂O_5.5F_3.5 in which the ruthenium centres are oxidised from +5 to +5.5 while the iron centres remain in a +3 oxidation state. While fluorination of the M = Ti leads to increasing itinerant electronic behaviour, fluorination of the M = Mn and Fe materials induces a twisting of the MX₆ octahedra that enables magnetic order to emerge at low temperatures. Finally, reaction of the SrO(SrVO₃)n (n = 1, 2, &infin;) series of phases with CaH₂ results in the formation of phases with composition SrO(SrVO₂H)_n (n = 1, 2, &infin;), the first examples of stoichiometric oxyhydride materials. SrVO₂H is magnetically ordered at room temperature, while the n = 1 and n = 2 materials order at 170 K and 240 K respectively. The high magnetic ordering temperature arises from strong interactions between (d_xy, d_yz) orbitals in a manner analogous to the reduced iron-containing phases SrO(SrFeO₂)_n.

The investigation into the syntheses and the intercalations of LDHs is the focus of the work described in this thesis. An introduction to Layered Double Hydroxide (LDH) materials with an emphasis on the possible host lattices and to their applications is given in <strong>Chapter 1</strong>. The application of LDHs in cement including; history of cement, cement production process, and cement hydration is detailed. The synthesis of the Ga-doped Ca₂Al(OH)₆Cl•nH₂O LDHs (Ca₂Ga_xAl_(1–x)-Cl; where 0 < x < 1) via the co-precipitation method is reported in <strong>Chapter 2</strong>. The effect of doping Ga³⁺ on a parameter of Ca₂Ga_xAl_(1–x)-Cl was determined by using Vegard’s law and the correlation between a parameter and x value was derived. The intercalation of organic anions including; sodium styrene sulfonate, sodium butene dicarboxylate, sodium fumarate and ammonium poly(styrene sulfonate), in Ca₂Ga-Cl structure is described. The intercalation of lignosulfonate, naphthalene sulfonate and polycarboxylate into Ca₂Al(OH)₆NO₃·6H₂O (Ca₂Al-NO₃) is detailed in <strong>Chapter 3</strong>. The release behaviour for the LDHs and the kinetic modelling of the release are reported. The effects of these LDHs on cement hydration studied by using the in situ X-ray diffraction and the ultrasound shear-wave reflection are discussed. In <strong>Chapter 4</strong>, the synthesis of Ca₂Al(OH)₆NO₃·nH₂O via a non-ionic surfactant reverse microemulsion is reported. The effects of the amount and the solubility [Hydrophile-Lipophile Balance (HLB)] of non-ionic surfactant on the morphology and the size distribution of the LDHs are discussed. Two new nitrite intercalated Ca₂Al-LDHs [Ca₂Al(OH)₆NO₂·nH₂O] synthesised via both the co-precipitation and the reverse micro-emulsion method are detailed in <strong>Chapter 5</strong>. The hydration of Portland cement samples with additive nitrate- and nitrite-intercalated Ca₂Al-LDH made using co-precipitation is discussed. The synthesis of dispersed, uniform nanoplatelet [Ca₂Al(OH)₆DDS]•H₂O LDHs is reported in <strong>Chapter 6</strong>. The effects of the amount of the surfactant on the morphology and size distribution of the LDHs are described. The experimental procedures and characterising techniques employed in this study are listed in <strong>Chapter 7</strong>. Additional data are provided in the <strong>Appendices</strong>.