In this thesis, we present results of studies of the electronic band structures and related electronic properties of some layered transition metal chalcogenides and their intercalation complexes. The materials investigated include group VIIc transition metal dichalcogenides, and 2H-TaS<SUB>2</SUB> and its lithium-, lead-, and tin-intercalated complexes, as well as dihafnium sulphide and selenide. Both experimental measurements and theoretical elect'onic band structure calculations have been carried out. The types of measurements conducted consist of reflectivity measurements in the energy range from 0.5 eV to 4.5 eV using the home-made reflectivity spectrometer, and electron energy loss measurements in the energy range up to 100 eV using the scanning transmission electron microscope as well as some characterization experiments (structural, chemical composition and thermal properties). The experimental investigations were restricted to the layered group VIIc metal dichalcogenides. All the electronic band structures are calculated using the linearized muffin-tin orbital (LMTO) method, and are reported for the first time except PdTe<SUB>2</SUB> and 2H-TaS<SUB>2</SUB>. The obtained electronic band structures for the Ni-group metal dichalcogenides, and the semiconductor-metal shift in progression from PtS<SUB>2</SUB> through PtSe<SUB>2</SUB> to PtTe<SUB>2</SUB> are discussed in terms of the binding energies of the atomic valence orbitals of the constituent atoms, the local coordination of the metal atoms and the symmetry of the crystals as well as the charge transfer effects. A superlattice structural phase transition is proposed for PtSe<SUB>2</SUB>, which may possibly explain the anomaly observed in the previous transport measurement. The previous photoemission spectra from NiTe<SUB>2</SUB>, PdTe<SUB>2</SUB> and PtTe<SUB>2</SUB>, and dHvA measurement on PdTe<SUB>2</SUB> are compared with their band structures in details, and a good agreement is found. Other available experimental data including the previous transport, optical and magnetic susceptibility measurements as well as the reflectivity and electron energy loss spectra measured in this work are also discussed in terms of these electronic structures. The band structure calculations for dihafnium chalcogenides predict that these materials are metals. They also suggest that there is a strong bonding between Hf atoms in the adjacent layers, thus giving rise to the rigidity in the c-direction which may preclude the intercalation of these materials. The results for 2H-TaS<SUB>2</SUB> and its intercalation complexes show that the rigid band model is essentially correct for 2H-LiTaS<SUB>2</SUB> but is an oversimplication for the post-transition metal intercalation compounds. Changes in the electronic structure upon intercalation are discussed in terms of the intercalant-host charge transfer and the hybridisation between the host states and the intercalation valence orbitals. Electrical conduction in 2H-PbTaS<SUB>2</SUB> and SnTaS<SUB>2</SUB> is found to be largely due to the p-valence electrons from the intercalant Pb (Sn) layers, resulting in the considerable increase in the superconducting transition temperature following intercalation. The results are also compared with the observed optical and transport properties and a broad agreement is found. The band structures and the electronic properties of other layered transition metal dichalcogenides and their intercalation complexes, as well as the band structure calculation techniques for the layered compounds are also reviewed in this thesis.

School of Chemistry, Faculty of Science, University of Witwatersrand, Johannesburg, South Africa Johannesburg, 2016 / The synthesis of pure layered clay minerals has to be evaluated at low temperatures, pressures and short reaction times to scale up to commercial processes. However, it has been discovered that under such reaction conditions, reactions experience considerable difficulties. Such difficulties include low yields of products that occur with associated other minerals, and long reaction times. Thus, the synthesis of synthetic clay minerals is commonly approached by the hydrothermal technique, which involves the crystallization of substances at high vapour pressures and temperatures. However, the employment of the hydrothermal technique is time- and water consuming, thus, the need for an energy-saving and reaction accelerating process method. In the work presented here particular interest is paid to the synthetic layered clay mineral pyrophyllite, which is used as a pressure transmitting medium in the making of synthetic diamond. As opposed to the hydrothermal technique, this work adopts the synthetic method resin gel for the synthesis of these layered materials. Preliminary results by Loren Purcell have shown that the resin-gel synthesis method has been able to make apparently layered materials that appear to have a thermal gravimetric profile that indicates a gradual mass loss of both surface and structural water. The work presented here reproduces these results and further explores other Si\Al ratio’s, silica and alumina precursors for the synthesis of pyrophyllite-like materials and the different heating methods of the gels. Transmission electron microscopy (TEM) shows that irrespective of the synthesis conditions sheet-like or platy crystals are formed. Scanning electron microscopy (SEM) confirms on the TEM observations and shows that the surface texture of the crystals has a compact appearance. Thermal gravimetric analysis (TGA) of the materials confirms on previous observations from preliminary results, materials indicate both adsorbed surface and interlayer water. Powder Xray diffraction (PXRD) is inconclusive of the determination of phase pure pyrophyllite. Furthermore, Brunauer-Emmett-Teller (BET) reveals that the materials are mesoporous solids and the materials were also characterised by DSC, Raman and HRTEM. / MT2016

Wan, Xi. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 128-132). Also available in electronic version.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xii, 134 p.; also includes graphics. Includes abstract and vita. Advisor: Noriko Katsube, Dept. of Mechanical Engineering. Includes bibliographical references (p. 121-125).

Semiconductors are characterized by atomic resolution imaging and density of states measurements (DOS) obtained through the use of a scanning tunneling microscope (STM). The DOS of the conduction and valence bands can be measured separately with a STM as opposed to an optical measurement which measures only the joint DOS. Layered-structure semiconductors are characterized both in the bulk form and in the isolated cluster form. Images of three bulk layered-structure semiconductors, MoS₂, WSe₂, and SnS₂, were obtained with both positive and negative sample-to-tip bias voltages. Curves of tunneling current as a function of bias voltage were measured, from which the DOS of the valence and conduction bands can be inferred. We obtained an atomically resolved image of an isolated fragment of a semi-conductor cluster which was deposited on a graphite surface from a colloidal suspension of BiI₃. Also imaged were clusters of MoS₂ layered-structure semiconductors.

Bismuth layer structure ferroelectrics (BLSFs) have attracted intensive investigation for the potential use in nonvolatile ferroelectric random access memory (NvRAM/FeRAM) and high temperature piezoelectric devices. In this thesis, there are three kinds of Bi-layered structure ferroelectric ceramics materials prepared by solid-state reaction methods. Investigations have been made on the crystal structure, surface morphology, and dielectric properties of these ferroelectric materials. In the chapter3 of this thesis, ferroelectric materials are SrBi2Ta2O9-based ceramics. One of the materials is SrBi2Ta2O9 composition with excess x wt% Bi2O3 (x=0, 2, and 4). Even 1280oC is used as the sintering temperature of stoichiometric SrBi2Ta2O9 composition, the X-ray diffraction patterns will show that the SrBi2Ta2O9 phase is coexisted with the raw material of Ta2O5 and the secondary phases of SrBi2O4 and BiTaO4. For SrBi2Ta2O9 composition with excess 2wt%- or 4wt%-Bi2O3-doped and sintered at 1040oC, the Ta2O5, SrBi2O4, and BiTaO4 phases are eliminated and only the SrBi2Ta2O9 phase is observed in the X-ray diffraction patterns. The other of SrBi2Ta2O9-based ceramics was doped with V2O5. V2O5 is used to substitute Ta2O5 of the SrBi2Ta2O9 ceramics to form SrBi2Ta2-xVxO9 composition, where x=0.1, 0.2, 0.3, and 0.4. For all SrBi2Ta2-xVxO9 composition, the crystal intensities of the (00l) planes (l =6, 8, 10, 12, and 14) increase with the increase of sintering temperature and saturate at 1050oC-sintered ceramics, and the increase in the crystal intensities of the (008) and (0010) planes are more obvious. For the same sintering temperature, the crystal intensities of the (00l) planes increase with the increase of V2O5 content and saturate at SrBi2Ta1.7V0.3O9 ceramics. In the chapter4, ferroelectric materials are SrBi4Ti4O15-based ceramics. One of the materials is (Sr1-xBax)Bi4Ti4O15 (x=0, 005, 0.1, 0.15, and 0.02), and BaO is used to substitute SrO. Dielectric properties were investigated in the temperature of 25oC~ 805oC at 1MHz. It is found that Curie temperatures are shifted to higher temperature as the BaO content increased. For (Sr1-xBax)Bi4Ti4O15 ceramics sintered at 1150oC, the Curie temperature for x=0, 0.05, 0.1, 0.15, and 0.2 are 645oC, 665oC, 705oC, 725oC, and 745oC, respectively. The other is non-stoichiometric compositions SrBi4Ti4O15+x Bi2O3, (x= -0.04, -0.02, 0, 0.02, and 0.04). From the observations of SEM, the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics reveal a two-phased grain growth, the bar-typed and the irregularly disk-typed grains coexist; The other ceramics will reveal the irregularly disk-typed grains. From the X-ray diffraction patterns, Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics. Except the SrBi3.96Ti4O14.94 ceramics, the other ceramics have revealed an unapparent splitting peak in the (119) plane. In the chapter5, ferroelectric materials are (Na0.5Bi0.5)TiO3-BaTiO3-based ceramics. The 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 (x= 0, 1, 2, and 3) ceramics were fabricated by two different processes. The first process is that (Na0.5Bi0.5)TiO3 and BaTiO3 composition was calcined at 850oC and 1100oC, respectly, and then the calcined (Na0.5Bi0.5)TiO3 and BaTiO3 powders were mixed in according to 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions. The second process was that the raw materials were mixed in accordance to the 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions and then calcined at 900oC. The sintering process was carried out in air for 2h from 1120oC to 1240oC. As the sintering temperatures are higher than 1160oC, the maximum dielectric constants of ceramics made by the second method are higher than those of ceramics by the first method, and the maximum dielectric constant of this ceramics will reveal in the x =1 ceramics. Both ceramics reveal a broaden dielectric constant-temperature curves. The other is (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3 compositions, where x= 0.03, 0.05, and 0.07, formatted by two different methods given above. The dielectric-temperature curves of (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3-based ceramics are almost unchanged as the measured frequency changed from 10 kHz to 1MHz.

No description available.

Thesis (Ph.D.)--Baylor University, 2007. / Includes bibliographical references (p. 107-109).

Thesis (Ph.D.)--McMaster University (Canada), 1993. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6259. Adviser: Jules P. Carbotte.