In the present thesis the reported results let us to conclude that the developed aqueous sol–gel procedure could be successfully used for the low-temperature synthesis of monophasic perovskite gadolinium aluminate ceramics. It was also demonstrated that the selection of raw materials for the sol–gel processing should be done with care. Monophasic perovskite structure gadolinium aluminate GdAlO3 has been synthesized by sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material and 1.2 ethanediol, natural tartaric acid, citric acid or mixture of citric acid and ethanolamine as complexing agent. According to the XRD results, the Gd2O3 instead of Gd(NO3)36H2O preferably should be used as starting material for the preparation of GdAlO3. Monophasic perovskite structure strontium substituted gadolinium aluminate Gd0.90Sr0.10AlO3– was synthesized by the same sol gel synthesis method at 1000 oC, using gadolinium oxide as gadolinium raw material, strontium nitrate as strontium ion source and EDTA as complexing agent. It was proved that better gadolinium ion source is gadolinium oxide than gadolinium nitate hexahydrate, better complexing agent – EDTA than natural tartaric acid in the synthesis of GdAlO3 and strontium substituted Gd1–xSrxAlO3– (x = 0.10, 0.25, 0.50, 0.75) samples. According to the XRD results, increasing amount of strontium reduces amount of peaks of perovskite structure gadolinium aluminate. Besides, 800 ºC temperature is too low for the... [to full text] / Šiame darbe vienfazis perovskito struktūros gadolinio aliuminatas GdAlO3 zolių-gelių metodu buvo gautas 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, kompleksus sudarančiu reagentu – 1,2 etandiolį, natūralią vyno rūgštį, citrinų rūgštį arba citrinų rūgšties ir etanolamino mišinį. Sintetinant GdAlO3, gautų tyrimų rezultatai parodė, kaip yra svarbu zolių gelių procese pasirinkti tinkamas pradines medžiagas bei kompleksus su metalais sudarančius reagentus: gadolinio jonų šaltiniu naudojant Gd2O3 buvo gauti geresni rezultatai nei naudojant Gd(NO3)3•6H2O, vienfazis GdAlO3 gali būti sėkmingai susintetintas kompleksus sudarančiu reagentu naudojant tiek natūralią vyno rūgštį, tiek 1,2 etandiolį, tiek citrinų rūgštį, tiek citrinų rūgšties ir etanolamino mišinį. Nustatyta, kad sintetinant stronciu pakeistus gadolinio aliuminatus Gd1–xSrxAlO3– (x = 0,10, 0,25, 0,50, 0,75), tinkamesnis gadolinio jonų šaltinis yra gadolinio oksidas nei gadolinio nitratas heksahidratas, kompleksus sudarantis reagentas – EDTA nei natūrali vyno rūgštis. Vienfazis perovskito struktūros stronciu pakeistas gadolinio aliuminatas Gd0,90Sr0,10AlO3– buvo susintetintas zolių-gelių metodu 1000 oC temperatūroje, gadolinio jonų šaltiniu naudojant Gd2O3, stroncio jonų šaltiniu – Sr(NO3)2, kompleksus sudarančiu reagentu – EDTA. Be to, 800 ºC iškaitinimo temperatūra yra per maža šiems junginiams sintetinti. Pirmą kartą pasiūlytas vandeninis zolių gelių metodas lantano ir gadolinio kobaltatams... [toliau žr. visą tekstą]

Carbonatites are igneous rocks comprising more than 50 modal percent of carbonate minerals and characterized by highly variable modal compositions. The majority of carbonatites are confined to intra-continental rifts, whereas occurrences associated with plate margins and orogenic settings are less common. Petrogenesis of carbonatites has been a matter of intense debate for several decades. The possible genetic models include crystallisation from a primary carbonatite magma, liquid immiscibility and crystal fractionation from carbonate-rich silicate magma. In contrast to the voluminous bulk-rock trace-element data and major-element analyses of minerals from carbonatites available in the literature, there has been no systematic study concerned with the trace-element signatures of the most common constituents of these rocks. This work is the first comprehensive study of the interrelations between the trace-element chemistry of the most common constituents of carbonatites, the geochemistry of these rocks, and their tectonic setting. The rock samples examined represent 21 different localities worldwide. The extent of major- and trace-element substitutions in amphibole, clinopyroxene, trioctahedral micas, dolomite, magnetite and perovskite is investigated in detail. The silicate minerals from carbonatites exhibit much larger compositional diversity than previously recognized. They can incorporate significant amounts of such petrogenetically important elements as Sr, REE, Zr, Nb and Ta. The majority of studied clino-amphibole- and clinopyroxene-group minerals exhibit previously unrecognized a bimodal distribution patterns of REE, which can be explained in terms of crystal chemistry of these phases. The trace-element signature of phlogopite from carbonatites, particularly Nb, Mn, Ni and Cr, is distinctly different from that of phlogopite from kimberlites, and can be used as a reliable petrogenetic indicator. Compositional variations in dolomite reflect magmatic and subsolidus processes in carbonatites. Magnetite from carbonatites follows a well-defined magmatic and previously unrecognized reaction trend. Contrary to prior studies, this mineral is only a minor host of HFSE in carbonatitic rocks. The U-Pb age data, trace-element and Sr-isotopic composition of perovskite from the Afrikanda carbonatite and clinopyroxenite suggest that the two rocks are not related by crystal fractionation. This study underlines the importance of a systematic approach in petrogenetic studies based on trace-element distribution.

Carbonatites are igneous rocks comprising more than 50 modal percent of carbonate minerals and characterized by highly variable modal compositions. The majority of carbonatites are confined to intra-continental rifts, whereas occurrences associated with plate margins and orogenic settings are less common. Petrogenesis of carbonatites has been a matter of intense debate for several decades. The possible genetic models include crystallisation from a primary carbonatite magma, liquid immiscibility and crystal fractionation from carbonate-rich silicate magma. In contrast to the voluminous bulk-rock trace-element data and major-element analyses of minerals from carbonatites available in the literature, there has been no systematic study concerned with the trace-element signatures of the most common constituents of these rocks. This work is the first comprehensive study of the interrelations between the trace-element chemistry of the most common constituents of carbonatites, the geochemistry of these rocks, and their tectonic setting. The rock samples examined represent 21 different localities worldwide. The extent of major- and trace-element substitutions in amphibole, clinopyroxene, trioctahedral micas, dolomite, magnetite and perovskite is investigated in detail. The silicate minerals from carbonatites exhibit much larger compositional diversity than previously recognized. They can incorporate significant amounts of such petrogenetically important elements as Sr, REE, Zr, Nb and Ta. The majority of studied clino-amphibole- and clinopyroxene-group minerals exhibit previously unrecognized a bimodal distribution patterns of REE, which can be explained in terms of crystal chemistry of these phases. The trace-element signature of phlogopite from carbonatites, particularly Nb, Mn, Ni and Cr, is distinctly different from that of phlogopite from kimberlites, and can be used as a reliable petrogenetic indicator. Compositional variations in dolomite reflect magmatic and subsolidus processes in carbonatites. Magnetite from carbonatites follows a well-defined magmatic and previously unrecognized reaction trend. Contrary to prior studies, this mineral is only a minor host of HFSE in carbonatitic rocks. The U-Pb age data, trace-element and Sr-isotopic composition of perovskite from the Afrikanda carbonatite and clinopyroxenite suggest that the two rocks are not related by crystal fractionation. This study underlines the importance of a systematic approach in petrogenetic studies based on trace-element distribution.

Transition metal oxides constitute a large class of materials with variety of very interesting properties and important technological utility. A subset with perovskite structure has been the subject matter of the current theoretical investigation with an emphasis on their electronic and structural behavior. An analytical and a computational method are used to calculate physical entities like lattice parameters, bulk moduli, band structures, density of electronic states and charge density distributions for various topologies. Results are discussed and compared with the available experimental findings.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 134-140).

Thesis (M.Eng.)(Metallurgical)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 322-338).

Thesis (Ph.D.) - University of St Andrews, April 2007.