Interest in these compounds centred on the bonding between the ethynyl groups and the metal atoms. The structures were determined by heavy atom techniques, and refined by the method of least squares, using three-dimensional data. Phenylethynyl(trimethylphosphine)copper(l), Me(_3)PCuC≡CPh, is tetrameric. The centresymmetric molecules are nearly flat, apart from the phosphine groups. The four copper atoms form a zig-zag chain, with Cu...Cu distances 2.45, 2.69, 2.4-5 Ǻ. Two phosphine groups are attached to each terminal copper atom. Two of the ethynyl groups lie on a line through the two inner copper atoms, to which they are σ-bonded. The other two are each 'side-on' bonded to an inner copper atom, with the bond to the phenyl group distorted away from the copper atom. Their terminal carbon atoms each form a bridge bond with two further copper atoms in the chain. Neglecting any copper- copper interaction, the coordination around the inner copper atoms is approximately trigonal, and around the terminal copper atoms, tetrahedral. Phenylethynyl(trimethylphosphine)silver(I), Me(_3)PAgCsC≡h , has silver atoms in infinite, almost straight, chains, with Ag...Ag = 3.03 Ǻ. Alternate silver atoms lie on centres of symmetry, and are σ-bonded to two ethynyl groups. These are 'side-on' bonded to adjacent silver atoms, which lie on two-fold axes, and which are bonded to two phosphine groups. The 'side-on' bonding is not symmetrical. (Ag-C = 2.55, 3.04 Ǻ.) The silver atoms are alternately in linear, and approximately tetrahedral, coordination. Phenylethynyl(isopropylamine)gold(I), (^i)PrfNH(_2)AuC≡CPh, has gold atoms in infinite zig-zag chains, related in pairs by two-fold axes. Au. ..Au = 3.72 2 Ǻ. along the chains, 3.27 Ǻ. Between chains. Each gold atom is linearly coordinated to an ethynyl carbon and an amine nitrogen atom, lying in the plane of the zig-zag. The arrangement excludes association through gold-ethynyl interaction, the shortest intermolecular distances being gold- gold or gold-nitrogen contacts.

The photoconductive and luminescent properties of cadmium sulphide have been of interest, and have only been studied extensively since 1947 when Frerichs reported a convenient method of preparing small single crystals. The properties of the material are summarised in Chapter two of this thesis, following an outline of the essential theory of electrical conduction in semiconductors. Conventional methods of single crystal preparation such as growth from the melt of from solution are not practicable with cadmium sulphide and most measurements have been made on small plates or rods grown by sublimation in a flow of carrier gas. However the preparation of large single crystal samples is desirable for certain measurements, e.g. Hall effect measurements, and essential if recent applications such as gamma-ray detectors or ultrasonic amplifiers are to be pursued. Various methods of growing large single crystals by sublimation have been reported, and these are reviewed in chapter 4. However crystal produced by similar methods can show marked differences in their properties. The resistivities of crystals as grown can be as high as 10(^10) ohm-cm., or as low as 1 ohm-cm, with wide variations in the carrier mobility. Close control of the properties of the material produced is essential for any application of for any detailed study of the material itself. The work which forms the basis of this thesis therefore consists of an investigation into the feasibility of growing large crystals by several methods. The effect on the resultant properties is observed when parameters such as the growth temperature or the partial pressures of the components are altered. The suitability of various starting material is also discussed. The conclusions from the present work are that departures from stoichiometry in the growth system are responsible for much of the difficulty in preparing large single crystals of good quality at low temperatures (~1050 C). Further, at the present time the properties of the material are controlled by departures from stoichiometry rather than by contamination from chemical impurities. The final section of the thesis indicates which of the reported methods is most suitable for small-scale production of large single crystals of high resistivity cadmium sulphide. It also described a growth method embodying the conclusions drawn from the present work as a basis for further study.

An experimental study has been made of the paramagnetic spin-lattice relaxation properties of some transition metal ions. Three trivalent metal ions were studied, namely those of titanium, chromium and ruthenium, in the form of acetyl-acetonate compounds of the general formula M (C(_5)H(_7)Q(_2))(_3). By the use of the corresponding diamagnetic aluminium or cobalt compounds, mixed single crystals were grown with various paramagnetic concentrations. Measurements were made at low temperatures in the liquid helium range, at X band microwave frequencies (9.3 KMc/s). Some measurements were also made at higher microwave frequencies (35.5 KMc/s).In all cases the relaxation behaviour observed in magnetically dilute crystals is in good agreement with the well established theories relating to single ion relaxation. Particular attention has been given however to the study of the relaxation processes in more concentrated crystals, where concentration dependent relaxation is found. The results obtained have been compared with the two theoretical suggestions that have been proposed to account for these effects. Although neither proposal is entirely satisfactory, the one involving exchange interactions within paramagnetic ion clusters is shown to account in a qualitative way for the observed behaviour. A detailed study of the E.F.R. spectrum of chromium doped crystals has been made which shows that significant exchange interactions do exist in these materials.

The domains structure of cobalt, gadolinium and terbium have been investigated; single crystals of gadolinium and terbium, were obtained in which the oxide content was considerably reduced by a solid state electrolysis technique. The Bitter technique has been used for most of the observations with a modified colloid, but a dry colloid technique has been used at temperatures below 240 K or higher than room temperature. Two different pieces of apparatus were designed for use at high or low temperatures. In the case of cobalt single crystals the results obtained at room, temperature are similar to those obtained previously. The pattern at 77 K was as expected from the anisotropy data. The lengths of daggers of reverse magnetization and the widths of their bases were found to be in direct proportion (for simple and complex daggers). The variation of the exchange constant A with temperature was also determined. It was not possible to observe a closure domain structure, however this did not rule out the possibility of a partial structure being present on the basal plane, though the variation of dam in width with temperature agrees best with that of Kittel model. The domain, structure of gadolinium was much easier to analyse than that of cobalt. At 274 K patterns on planes containing the c-axis shoved parallel l80 walls, with the development of partial closure structures at the surface near the basal plane and at the oxide inclusions. Basal plane patterns indicate that the l80 vails are not plane and give more detailed information about the mixed nature of the basal structure. The change in domain structure has been studied as the temperature is reduced to 77 K and under the influence of magnetic fields up to l400 Oe. Unexpected results were obtained when the normal field produced by a permanent magnet was applied to the basal plane. Such arrangements produced the well known honeycomb structure which was observed on other materials after an applied field of few K.Oe. was applied parallel or perpendicular to the c-axis. This was believed to be the result of a closure structure with magnetisation laid freely in basal plane. The non-uniformity of' the lines of force produced by such magnet will re-orient the direction of the magnetic moment within the closure region. The domain structure in a cube shaped terbium single crystal was observed at 210 K and different possibilities for the internal configuration were given. Agreement between experimental observation and the proposed model which consists of plate type domains magnetized along the b(_1) and b(_2) axis but not along the third axis b(_3)-axis, which is perpendicular to one surface. The equilibrium, width was measured and compared with the calculated one and they were in. good agreement. The structure at lower temperatures was studied. However as in gadolinium it is still not clear whether the pattern observed at low temperature represents a true domain structure.

No description available.

A study has been made of the compounds formed in the system SrO-Al₂O₃-H₂O under varying conditions of temperature and pressure. The hydrates prepared included S. AHg and SAHn, both of which have been known for some time, and S.A.H. which was recently reported by other workers. Several new hydrates were prepared hydrothermally: SAH, SgAH and S.A.H. SAH and S.A.H. had been described previously as SyiH. and Sj-A. respectively. The compounds prepared were investigated by X-ray diffraction methods, optical microscopy, differential thermal analysis, thermograviroetric analysis, static thermal analysis, infra-red spectroscopy and density measurement. Single crystal X-ray methods were used to determine the space group, cell dimensions and cell contents cf the new compounds prepared. An attempt was made to determine the structure of SAH, as the structure of the isomorphous barium compound has been only partially solved. However, the available crystals were too small to give good intensity data. The structure of S"A, which is isomorphous with Cl whose structure hss long been a problem, was also studied. Again, poor intensity data prevented a complete solution. The inversion of SA at high temperatures to a structure resembling that of BA was studied, using differential thermal analysis and X-ray techniques. Finally, a comparison was made of the methods of preparation and structures of the aluminate hydrates of the three alkaline earths calcium, strontium and barium.

The crystal structure Of α-rhamnose monohydrate has been determined by the interpretation of the three dimensional Patterson function, and refined on two projections using diffraction data derived from Geiger counter measurements. There are possibly significant deviations from the expected values of three bond lengths, which include both the axial C-OH bonds of the molecule, one of which is short, as in α-glucose, and the other long. There are several significant deviations from the tetrahedral angle in the bond angles; that at the oxygen atom of the ring is 120° and those made by the extracyclic substituents appear to indicate a repulsion between them. The crystal packing is determined by hydrogen bonds, in which all the oxygen atoms and the water molecule take part, and in which all the available hydrogen atoms are utilised. The hydrogen atoms appear with moderate definition on (F0 - Fc) syntheses but their positions are not completely unambiguous largely owing to the non-centrosymmetrical nature of the crystal, the poor resolution of the atoms in projection and the occurrence of anisotropic thermal vibrations of the atoms, for which no corrections were made.

No description available.

No description available.

The work presented is a study of nematic liquid crystal physical properties. One of the phenomenon investigated is the bistability or in other words, the ability of the director of the material to rest in different orientations as function of the geometry of the sidewall. The main core of this research is the study of exoelectric effect and ionic contamination within the nematic layer. This can be split into three approaches. In the first part, the exoelectric coefficients are determined from the distortion of a nematic liquid crystal in response to non uniform electric fields created using an interdigitated electrode architecture. The distortion was deduced from the fringes movement in a Mach-Zhender interferometer built especially for this investigation. In the second part, the transient capacitance technique is used to measure the permittivity response of two homogeneous nematic materials subjected to different electric signal waveforms. The results remain to be fitted in order to give an alternative method to deduce the exoelectric coefficients values and a better understanding of the effect of ionic contamination. The last part of the work relates to the determination of the exoelectricity coefficients and ionic contamination and their effects on the Fréedericksz transition in homogeneous nematic liquid crystal using magnetic fields. The Mach-Zhender interferometer was also used to investigate two other phenomena, the first one is electrophoresis and the second is the resonance mode of insects.