Uma célula de pressão do tipo pistão-cilindro fabricada com BeCu foi utilizada na realização de medidas de transporte eletrônico (resistividade elétrica ½) sob pressão hidrostática P e como função da temperatura T. O procedimento de montagem do arranjo experimental compreendeu: (i) elaboração de novos acessórios para a célula de pressão, (ii) calibração do sensor de temperatura e (iii) calibração do sensor de pressão. A montagem e calibração da célula de pressão foram realizadas com sucesso e o resultado desse trabalho de instrumentação é que a referida célula pode operar no intervalo de temperatura compreendido entre 77 e 350 K e sob pressões tão altas quanto » 9.0 kbar. Uma característica dos procedimentos utilizados é que a determinação dos parâmetros termodinâmicos T e P é realizada de maneira precisa, de tal forma que P pode ser inferida exatamente em qualquer valor de temperatura. Para a realização de um estudo sistemático das propriedades de transporte eletrônico utilizando a referida célula de pressão, uma família de óxidos de níquel foi escolhida. Os compostos cerâmicos Nd1¡xEuxNiO3; x = 0, 0.10, 0.15, 0.25, 0.30 e 0.35; apresentam uma transição de fase metal-isolante MI em um amplo intervalo de temperatura 200 T 350 K. Além disso, esses compostos exibem uma histerese térmica entre as medidas de aquecimento e resfriamento, que caracteriza a transição de fase MI como sendo de primeira ordem. Por outro lado, a amostra com x =0.35 não apresenta histerese térmica e, por isso, a transição de fase MI é caracterizada como sendo de segunda ordem. Em especial, esses compostos quando submetidos a variações de pressão hidrostática apresentam diferentes magnitudes da temperatura de transição de fase metal-isolante TMI, exibindo forte dependência dos parâmetros termodinâmicos P e T. Um estudo sistemático acerca da característica da transição de fase MI sob variação dos parâmetros termodinâmicos P e T foi realizado via medidas de resistividade elétrica sob pressão e como função da temperatura ½(P; T). Os resultados obtidos são utilizados no mapeamento da dependência de TMI como função de P para cada material. O diagrama de fases TMI versus P evidencia duas regiões: uma isolante e outra metálica, para todos os compostos estudados. Ainda acerca do diagrama de fases, a relação dTMI dP foi estimada e valores de » - 4.4 K/kbar foram obtidos para x < 0.15, ou seja, para os compostos com x = 0, 0.10 e 0.15, o valor de dTMI dP foi observado ser praticamente constante. Esses compostos encontram-se no limite de diluição (x 0.165), onde as propriedades dos materiais são alteradas de maneira suave e, portanto, similares às da matriz NdNiO3. Contudo, os compostos com x > 0.15 possuem taxas de variação dTMIdP crescentes como função do aumento da substituição de Nd por Eu e preservam a ocorrência de uma histerese térmica, mas com intervalos ¢T muito menos pronunciados (da ordem de alguns K). No caso da amostra com x = 0.35 a histerese térmica não é observada à pressão atmosférica, mas ocorre de forma sistemática com a aplicação de P. Logo, a aplicação de P e/ou substituição de Nd por Eu podem alterar o caráter da transição de fase de segunda para primeira ordem, ou vice-versa, nessa família de óxidos. / A piston-cylinder self-clamping pressure cell made of BeCu was used to perform electronic transport measurements (electrical resistivity ½) as a function of temperature T and under hydrostatic pressure P. The procedure for assembly of the experimental arrangement included: (i) development of new accessories for the cell pressure, (ii) temperature sensor calibration and (iii) pressure sensor calibration. The assembly and calibration of the pressure cell were performed successfully, and the result of this experimental work is that of this cell can operate in a range of temperature between 77 and 350 K and under pressures as high as » 9.0 kbar. A feature of the procedures developed is that determination of thermodynamics parameters T and P is performed accurately, so that P can be determined exactly at any temperature. To perform a systematic study of the electronic transport properties using the self-clamped cell, a family of nickel oxides was chosen. The ceramic compounds Nd1¡xEuxNiO3; x = 0, 0.10, 0.15, 0.25, 0.30 e 0.35; exhibit a metal-insulator MI phase transition in a broad range of temperature 200 T 350 K. Besides, these compounds display a thermal hysteresis between measures of heating and cooling, which characterizes the MI transition as a first order phase transition. Except to x = 0.35 that does not show the thermal hysteresis and, therefore, the MI phase transition is characterized as of the second order. In particular, this compound when submitted to variations of hydrostatic pressure have different magnitude of the metal-insulator phase transition temperature TMI showing strong dependence of thermodynamics parameters P and T. The systematic study regarding the properties of the MI phase transition subject to changes in thermodynamic parameters P and T was done by measurements of electrical resistivity under pressure and as a function of temperature ½(P; T). The results are used to map the dependence of TMI as a function of P for each material. The phase diagram of TMI versus P shows a broadenring line that exhibits two regions: one insulating and other metallic, to all compounds studied. Also on the phase diagram, the ratio of dTMI dP was estimated values of » -4.4 K/kbar were obtained for x < 0.15, or for compounds with x = 0, 0.10 and 0.15, the value of dTMIdP was observed to be almost constant. These compounds are at the limit of dilution (x 0.165), where properties of the materials are changed softly and therefore similar to the matrix NdNiO3. On the other hand, the compounds with x > 0.15 have rates of change dTMIdP growing as a function of increase the replacement of Nd by Eu and preserve the occurrence of a thermal hysteresis, but with intervals T much less pronounced (the order of some K). In the case of sample with x = 0.35 the thermal hysteresis is not observed at atmospheric pressure, but occurs systematically under aplied P. Hence, the application of P and/or replacement of Nd by Eu can change the character of the phase transition from second to first order, or vice versa, in this family of oxides.

Abstract not available

An investigation of the geological resources of the Southern Highlands was undertaken and over two hundred samples were collected and examined for possible use as stoneware ceramic ingredients. Thirty four of these samples were tested for possible use as clay body ingredients, while sixty five samples were selected for assessment as glaze ingredients. A wood fired kiln was built from firebricks produced from a local deposit of a white bauxite related material. Materials selected as a result of these tests were combined to create ceramic objects fired at stoneware temperatures. The most interesting result of the investigation was the discovery of a number of small weathered dykes and sills, samples from which were developed into workable ceramic clay bodies and glazes using a simple empirical testing procedure. A previously unknown excellent white translucent native porcelain stone or ‘bai tunze’ was discovered and developed into a workable porcelain body. Some iron stained porcelain bodies that ‘flashed’ red in the wood firing kiln were also developed. Exhibitions of the creative work produced were shown in the ‘Legge Gallery’, a Fine Art gallery in Sydney. Two critical reviews of those shows appeared in the magazine Craft Arts International, No. 64, 2005, pp 106-107 and The Journal of Australian Ceramics, Vol 46 #1 pp 21-24. Several papers were published detailing various aspects of the research: “The Search for Raw Materials in the Southern Highlands” in The Journal of Australian Ceramics, Vol 41#3, pp 22-23; “Flotation – A method of refining useful minerals”, in The Journal of Australian Ceramics, Vol 41#3, pp 24-25; “Magic Dirt” in The Journal of Australian Ceramics, Vol 46 #1 pp 76-79; “New work from an old landscape”, in Ceramics Technical, 24, 2007. pp 45-52;“From the ground up”, in Ceramic review, issue 222, 2006, pp 54-55. The research concludes that the Southern Highlands of New South Wales is geologically rich in suitable materials for the production of stoneware ceramics and that there are a few specific bai tunze like materials that are very interesting and have considerable aesthetic potential. The research determined that these bai tunze like materials are potentially capable of being developed into clay bodies and glazes of great beauty. / Doctor of Philosophy (PhD)

An investigation of the geological resources of the Southern Highlands was undertaken and over two hundred samples were collected and examined for possible use as stoneware ceramic ingredients. Thirty four of these samples were tested for possible use as clay body ingredients, while sixty five samples were selected for assessment as glaze ingredients. A wood fired kiln was built from firebricks produced from a local deposit of a white bauxite related material. Materials selected as a result of these tests were combined to create ceramic objects fired at stoneware temperatures. The most interesting result of the investigation was the discovery of a number of small weathered dykes and sills, samples from which were developed into workable ceramic clay bodies and glazes using a simple empirical testing procedure. A previously unknown excellent white translucent native porcelain stone or ‘bai tunze’ was discovered and developed into a workable porcelain body. Some iron stained porcelain bodies that ‘flashed’ red in the wood firing kiln were also developed. Exhibitions of the creative work produced were shown in the ‘Legge Gallery’, a Fine Art gallery in Sydney. Two critical reviews of those shows appeared in the magazine Craft Arts International, No. 64, 2005, pp 106-107 and The Journal of Australian Ceramics, Vol 46 #1 pp 21-24. Several papers were published detailing various aspects of the research: “The Search for Raw Materials in the Southern Highlands” in The Journal of Australian Ceramics, Vol 41#3, pp 22-23; “Flotation – A method of refining useful minerals”, in The Journal of Australian Ceramics, Vol 41#3, pp 24-25; “Magic Dirt” in The Journal of Australian Ceramics, Vol 46 #1 pp 76-79; “New work from an old landscape”, in Ceramics Technical, 24, 2007. pp 45-52;“From the ground up”, in Ceramic review, issue 222, 2006, pp 54-55. The research concludes that the Southern Highlands of New South Wales is geologically rich in suitable materials for the production of stoneware ceramics and that there are a few specific bai tunze like materials that are very interesting and have considerable aesthetic potential. The research determined that these bai tunze like materials are potentially capable of being developed into clay bodies and glazes of great beauty. / Doctor of Philosophy (PhD)

The crystal chemistry of Fe doped mayenite (Ca12Al14-xFexO33) samples prepared using solid state and sol-gel synthesis techniques were compared. Five samples were prepared using solid state process with varying Fe concentration (x) where x = 0, 0.05, 0.1, 0.25 and 0.3; two sets of samples were made via the sol-gel, the first set was prepared for studying the amount of Fe substituted by varying the Fe concentration where x = 0, 0.05, 0.1, 0.2, 0.3 and 0.4 and the second set was prepared for studying the firing temperature and did not contain Fe additions (x = 0). Samples produced via the sol-gel method were more likely to be single phase with incorporation of Fe2O3 while solid state samples contained multiple phases over the same range of Fe2O3 substitutions. The refined lattice parameters, of samples prepared using both methods were observed to increase with increasing Fe concentration, suggesting Fe is replacing Al since Fe has larger ionic radii than Al. Samples prepared via the sol-gel method were found to be single phase at lower temperatures compared to samples prepared via solid state synthesis. Samples synthesized using the sol-gel method were found to have multiple phases when fired at 800 ˚C but were single phase when fired at 900˚C. In comparison, samples synthesized using traditional solid state techniques showed single phase when fired at a temperature of 1350˚C.

Single crystals with composition Lu3Al5O12 were synthesized using Czochralski and micro-pulling-down melt growth techniques. Polycrystalline ceramics of the same composition were synthesized by vacuum annealing of powders prereacted using a citrate-nitrate combustion technique and by spark-plasma-sintering of powders prereacted using a flame-spray-pyrolysis technique. Single crystals and polycrystalline ceramics are activated with Ce3+ or Pr3+ or doubly activated with Ce3+ and Tb3+ ions. Cerium-doped Czochralski-grown single crystals were compared to cerium-terbium codoped Czochralski-grown and micro-pulling down single crystals. Cerium-terbium codoped single crystals are also compared to similarly-activated polycrystalline ceramics sintered under vacuum using combustion-synthesized prereacted powders. X-ray diffraction analysis and fluorescence characterization were used to determine successful formation of single-phase LuAG and successful incorporation of doping species. Absorbance, fluorescence, radioluminescence, and scintillation decay analyses were used to compare synthesis processes and activator selection.

Single crystals with composition Lu3Al5O12 were synthesized using Czochralski and micro-pulling-down melt growth techniques. Polycrystalline ceramics of the same composition were synthesized by vacuum annealing of powders prereacted using a citrate-nitrate combustion technique and by spark-plasma-sintering of powders prereacted using a flame-spray-pyrolysis technique. Single crystals and polycrystalline ceramics are activated with Ce3+ or Pr3+ or doubly activated with Ce3+ and Tb3+ ions. Cerium-doped Czochralski-grown single crystals were compared to cerium-terbium codoped Czochralski-grown and micro-pulling down single crystals. Cerium-terbium codoped single crystals are also compared to similarly-activated polycrystalline ceramics sintered under vacuum using combustion-synthesized prereacted powders. X-ray diffraction analysis and fluorescence characterization were used to determine successful formation of single-phase LuAG and successful incorporation of doping species. Absorbance, fluorescence, radioluminescence, and scintillation decay analyses were used to compare synthesis processes and activator selection.

The crystal chemistry of Fe doped mayenite (Ca12Al14-xFexO33) samples prepared using solid state and sol-gel synthesis techniques were compared. Five samples were prepared using solid state process with varying Fe concentration (x) where x = 0, 0.05, 0.1, 0.25 and 0.3; two sets of samples were made via the sol-gel, the first set was prepared for studying the amount of Fe substituted by varying the Fe concentration where x = 0, 0.05, 0.1, 0.2, 0.3 and 0.4 and the second set was prepared for studying the firing temperature and did not contain Fe additions (x = 0). Samples produced via the sol-gel method were more likely to be single phase with incorporation of Fe2O3 while solid state samples contained multiple phases over the same range of Fe2O3 substitutions. The refined lattice parameters, of samples prepared using both methods were observed to increase with increasing Fe concentration, suggesting Fe is replacing Al since Fe has larger ionic radii than Al. Samples prepared via the sol-gel method were found to be single phase at lower temperatures compared to samples prepared via solid state synthesis. Samples synthesized using the sol-gel method were found to have multiple phases when fired at 800 ˚C but were single phase when fired at 900˚C. In comparison, samples synthesized using traditional solid state techniques showed single phase when fired at a temperature of 1350˚C.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 206-210). Available also in a digital version from Dissertation Abstracts.

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