No description available.

Cerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be enhanced in the nanoceria. In most the practical scenarios, it is necessary to have a stable suspension of ceria nanoparticles (CNPs) over longer periods of time. However, the existing literature is confined to short term studies pertaining to synthesis and property evaluation. Having understood the need for a comprehensive understanding of the CNP suspensions, this dissertation is primarily aimed at understanding the behavior of CNPs in various chemical and physical environments. We have synthesized CNPs in the absence of any surfactants at room temperature and studied the aging characteristics. After gaining some understanding about the behavior of this functional oxide, the synthesis environment and aging temperature were varied, and their affects were carefully analyzed using various materials analysis techniques such as high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS). When the CNPs were aged at room temperature in as-synthesized condition, they were observed to spontaneously assemble and evolve as fractal superoctahedral structures. The reasons for this unique polycrystalline morphology were attributed to the symmetry driven assembly of the individual truncated octahedral and octahedral seed of the ceria. HRTEM and Fast Fourier Transform (FFT) analyses were used to explain the agglomeration behavior and evolution of the octahedral morphology. Some of the observations were supported by molecular dynamic simulations. Poly (ethylene glycol) (PEG) and ethylene glycol (EG) were used to control the kinetics of this morphology evolution. The ability to control the agglomeration of CNPs in these media stems from the lower dielectric constant and an increased viscosity of the EG and PEG based solvents. CNPs when synthesized and aged in frozen conditions, i.e. in ice, were found to form one dimensional, high aspect ratio structures. A careful analysis has provided some evidence that the CNPs use the porous channels in ice as a template and undergo oriented attachment to form nanorods. When the aging treatment was done near freezing temperature in solution, the nanorods were not observed, confirming the role of channels in ice. When synthesized in aqueous media such as DI water, PEG and EG; CNPs were observed to exhibit a reversible oxidation state switching between +3 and +4. Band gap values were computed from the optical absorption data. The changes in the band gap values observed were attributed to the changes in the oxidation state of CNPs as opposed to the quantum confinement effects, as expected in other nanoparticle systems. The work presented in this dissertation demonstrates, with evidence, that in order to obtain a comprehensive understanding of the properties of nanoscale materials it is of paramount importance to monitor their behavior over relatively longer periods of time under various ambient environments. While the solution based techniques offer a versatility and low cost route to study the fundamental properties of nanomaterials, they suffer some inherent problems such as precursor contamination and uncontrolled chemical reactions. Especially when analyzing the behavior of ceria-based materials for applications like solid oxide fuel cells, a great control in the density and crystalline quality are desired. In order to achieve this, as a first step pure ceria thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The ceria films were analyzed using various in situ and ex situ techniques to study the crystal structure, growth mode and epitaxial quality of the films. It was observed that the epitaxial orientation of the ceria films could be tuned by varying the deposition rate. When the films were grown at low deposition rate (< 8 Å/min) ceria films with epitaxial (200) orientation were observed where as the films grown at high deposition rates (up to 30 Å/min) showed (111) orientation. Theoretical simulations were used to confirm some of the experimental facts observed in both nanoparticles and thin films.

No description available.

No description available.

Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is considered. / Tiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille. / Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., &amp; Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., &amp; Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., &amp; Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046

A new family of oligonuclear cyano compounds incorporatingtransition (Pt) and main group (Tl) metals bound with anon-buttressed Pt-Tl bond was synthesised in aqueous solution.The metal-metal linkage is formed in the reaction betweenplatinum and thallium in their stable oxidation forms, Pt(II)and Tl(III), orvice versa: Pt(IV) and Tl(I). Four binuclear complexeswith a general composition [(CN)5Pt-Tl(CN)n(aq)]n-(n = 0-3) and a trinuclear species [(NC)5Pt-Tl-Pt(CN)5]3-were identified and structurally characterised insolution by multinuclear NMR, EXAFS and vibrationalspectroscopy. In aqueous solution the complexes exist inequilibrium. The distribution between the species can bealtered by varying the molar ratio Pt/Tl, cyanide concentrationand pH. Stability constants of the compounds weredetermined. A new compound (NC)5PtTl was also prepared in solid and its crystalstructure solved by a combination of X-ray powder diffractionand EXAFS. Altogether the values of195Pt-205Tl spin-spin coupling constants (25-71 kHz),interatomic Pt-Tl distances (2.598-2.638 Å), and vibrationstretching frequencies v (Pt-Tl) (159-164 cm-1) are fully indicative of a direct and unsupportedPt-Tl bond. The calculated values of Pt-Tl force constants(1.56-1.74 N· cm-1) are characteristic for single metal-metal bond.The oxidation status in the compounds can be viewed asintermediate between II and IV for platinum, and between I andIII for thallium, as reflected by the chemical shifts of195Pt and205Tl nuclei, C≡ N stretching frequencies andelectron binding energies. The compounds are capable to undergo a photoinducedtwo-electron transfer between the coupled hetero-metal ions.Upon irradiation into the metal-to-metal charge transferabsorption band, effective photoredox reaction takes place. Itresults in scission of the Pt-Tl bond and formation of variouscomplexes of oxidised platinum (Pt(III, IV)) and reducedthallium (Tl(I)). The values of photodecomposition quantumyields were determined from a stationary photolysis study ofthe heterometallic complexes. Nanosecond laser flash photolysisof the heteronuclear Pt-Tl cyano compounds was performed in thetimescale range 1· 10-6- 5· 10-2s and several intermediate species were detectedand characterised by optical spectroscopy. The heteronuclear Pt-Tl cyano compounds can be furthermodified in terms of their stability, solubility, and lightabsorption characteristics. It has been found that the platinumpentacyano unit of the [(NC)5Pt-Tl(CN)n(aq)]n-species is inert towards the tested ligands,whereas the thallium "part" of the complexes can be tunedsignificantly. A number of complexes [(NC)5Pt-Tl(L)m]x-(L-ligand) were prepared and characterised insolution. Compounds [(NC)5Pt-Tl(nta)(H2O)]3-, [(NC)5Pt-Tl(bipy)(DMSO)3], and [(NC)5Pt-Tl(bipy)2]have been prepared in solid and their structuresdetermined by single-crystal X-ray diffraction. <b>Keywords:</b>thallium, platinum, cyanide, metal-metal bond,non-buttressed, heterobimetallic, photoinduced, electrontransfer, redox reaction, NMR, chemical shift, spin-spincoupling constant, Raman, EXAFS, X-ray diffraction,equilibrium, oxidation state, oxidative addition,photolysis

<p>A new family of oligonuclear cyano compounds incorporatingtransition (Pt) and main group (Tl) metals bound with anon-buttressed Pt-Tl bond was synthesised in aqueous solution.The metal-metal linkage is formed in the reaction betweenplatinum and thallium in their stable oxidation forms, Pt(II)and Tl(III), or<i>vice versa</i>: Pt(IV) and Tl(I). Four binuclear complexeswith a general composition [(CN)₅Pt-Tl(CN)_n(aq)]^n-(n = 0-3) and a trinuclear species [(NC)₅Pt-Tl-Pt(CN)₅]^3-were identified and structurally characterised insolution by multinuclear NMR, EXAFS and vibrationalspectroscopy. In aqueous solution the complexes exist inequilibrium. The distribution between the species can bealtered by varying the molar ratio Pt/Tl, cyanide concentrationand pH. Stability constants of the compounds weredetermined.</p><p>A new compound (NC)₅PtTl was also prepared in solid and its crystalstructure solved by a combination of X-ray powder diffractionand EXAFS. Altogether the values of¹⁹⁵Pt-²⁰⁵Tl spin-spin coupling constants (25-71 kHz),interatomic Pt-Tl distances (2.598-2.638 Å), and vibrationstretching frequencies v (Pt-Tl) (159-164 cm^-1) are fully indicative of a direct and unsupportedPt-Tl bond. The calculated values of Pt-Tl force constants(1.56-1.74 N· cm^-1) are characteristic for single metal-metal bond.The oxidation status in the compounds can be viewed asintermediate between II and IV for platinum, and between I andIII for thallium, as reflected by the chemical shifts of¹⁹⁵Pt and²⁰⁵Tl nuclei, C≡ N stretching frequencies andelectron binding energies.</p><p>The compounds are capable to undergo a photoinducedtwo-electron transfer between the coupled hetero-metal ions.Upon irradiation into the metal-to-metal charge transferabsorption band, effective photoredox reaction takes place. Itresults in scission of the Pt-Tl bond and formation of variouscomplexes of oxidised platinum (Pt(III, IV)) and reducedthallium (Tl(I)). The values of photodecomposition quantumyields were determined from a stationary photolysis study ofthe heterometallic complexes. Nanosecond laser flash photolysisof the heteronuclear Pt-Tl cyano compounds was performed in thetimescale range 1· 10^-6- 5· 10^-2s and several intermediate species were detectedand characterised by optical spectroscopy.</p><p>The heteronuclear Pt-Tl cyano compounds can be furthermodified in terms of their stability, solubility, and lightabsorption characteristics. It has been found that the platinumpentacyano unit of the [(NC)₅Pt-Tl(CN)_n(aq)]^n-species is inert towards the tested ligands,whereas the thallium "part" of the complexes can be tunedsignificantly. A number of complexes [(NC)₅Pt-Tl(L)_m]^x-(L-ligand) were prepared and characterised insolution. Compounds [(NC)₅Pt-Tl(nta)(H₂O)]^3-, [(NC)₅Pt-Tl(bipy)(DMSO)₃], and [(NC)₅Pt-Tl(bipy)₂]have been prepared in solid and their structuresdetermined by single-crystal X-ray diffraction.</p><p><b>Keywords:</b>thallium, platinum, cyanide, metal-metal bond,non-buttressed, heterobimetallic, photoinduced, electrontransfer, redox reaction, NMR, chemical shift, spin-spincoupling constant, Raman, EXAFS, X-ray diffraction,equilibrium, oxidation state, oxidative addition,photolysis</p>

Um einen besseren Zugang zum Verständnis struktureller Eigenschaften von den ternären Verbindungen des Systems Yb–Pd–Ga zu bekommen, wurden zunächst die Ordnungs- und Unordnungsbeziehungen sowie die chemische Bindung in den Kristallstrukturen binärer Pd–Ga- bzw. Yb–Ga-Verbindungen analysiert. Im Rahmen der phasenanalytischen Untersuchungen des binären Systems Yb–Ga konnte eine neue Verbindung charakterisiert werden (Ytterbiumpentagallid). Für den galliumreichen Teil des ternären Phasendiagramms Yb–Pd–Ga wurde ein isothermer Schnitt bei 600 °C erstellt (&amp;gt; 50 At.-% Ga). Die Homogenitätsbereiche der untersuchten Verbindungen wurden metallographisch bzw. röntgenographisch bestimmt. Die Kristallstrukturen wurden aus Röntgen-Einkristalldaten bestimmt. In den Kristallstrukturen wurden drei unterschiedliche Arten von Unordnung beobachtet (Substitutionsunordnung, Symmetrie-Brechung, Positionsunordnung). Für eine Reihe von Verbindungen des Systems Yb–Pd–Ga wurde der elektronische Zustand von Yb bestimmt. Dies gelang mit Hilfe von Messungen der magnetischen Suszeptibilität bzw. mit der Röntgen-Absorptionsnahkantenspektroskopie.

La formation des noyaux planétaires métalliques est un évènement majeur pour l’évolution des propriétés physico-chimiques des planètes telluriques telles que nous les connaissons aujourd’hui. En effet, l’abondance des éléments sidérophiles (i.e. qui ont des affinités chimiques avec les phases métalliques) dans les manteaux planétaires s’explique par les conditions dans lesquelles se sont séparées les phases métalliques et silicatées. Au premier rang de ces conditions se trouvent la pression, la température et la fugacité d’oxygène. La distribution des éléments dans le noyau et le manteau ne peut en effet s’expliquer que pour un équilibre obtenu dans un océan magmatique profond, donc à haute pression et haute température ; et dans des conditions d’oxydo-réduction variables, dont l’évolution la plus probable est de passer d’un état réduit à un état oxydé. Un autre paramètre important est la présence ou non d’eau dans l’océan magmatique primitif. En effet, nous disposons de plus en plus d’arguments permettant d’expliquer l’arrivée des éléments volatils, notamment l’eau, pendant l’accrétion, à partir de briques élémentaires qui contiennent ces éléments. Si l’eau est présente tout au long de l’accrétion, et donc pendant la ségrégation du noyau, elle peut donc avoir un effet sur ce dernier phénomène. Dans cette hypothèse, nous avons mené des expériences de haute pression et haute température permettant de modéliser expérimentalement la formation du noyau en condition hydratée. Ces expériences nous ont permis de montrer que la présence d’eau a un effet sur l’évolution de l’état d’oxydation des manteaux planétaires. Cette évolution oxydo-réductive nous a permis de contraindre des modèles d’accrétion basés sur un mélange de chondrites EH et CI, qui confirment des modèles construits à partir de données isotopiques. Ces modèles nous ont permis de contraindre les concentrations primitives maximum en eau probables sur Terre (1,2-1,8 % pds.) et sur Mars (2,5-3,5 % pds.). D’autre part, nos avons mis en évidence le caractère lithophile (i.e. qui a des affinités chimiques avec les phases silicatées) de l’hydrogène à haute pression, a contrario de plusieurs études précédentes. De ce fait, la différence entre les concentrations initiales élevées en eau que nous obtenons dans nos modèles d’accrétion et les concentrations en eau estimées sur Terre et sur Mars actuellement (2000 ppm et 200 ppm, respectivement) ne peut pas être expliquée par un réservoir d’hydrogène dans le noyau. Enfin, pour améliorer les modèles de formation du noyau, nous avons mis en évidence, par des modèles numériques, l’effet important de la viscosité de l’océan magmatique sur le taux d’équilibre entre noyaux et manteaux des planètes telluriques. Cela nous mène à ré-évaluer les modèles de formation des planètes telluriques basés sur des résultats expérimentaux à l’équilibre, notamment l’extension maximale de l’océan magmatique. L’évolution de la viscosité de l’océan magmatique a donc un impact important sur la composition finale des noyaux planétaires (par exemple les teneurs en soufre, oxygène ou silicium des noyaux terrestres et martiens). / The formation of the metallic planetary cores is a major event regarding to the evolution of physical and chemical properties of the telluric planets as we know it today. Indeed, the siderophile elements (i.e. which has affinities with metallic phases) abundances in planetary mantles is explained by the conditions of core-mantle segregation. Among these conditions, pressure, temperature and oxygen fugacity are the main ones controlling distribution of the elements between mantle and core. This distribution can only be explained by an equilibrium between metal and silicate obtained in a deep magma ocean, which implies high pressure and high temperature of equilibrium. Moreover, the oxygen fugacity must have varied during core-mantle segregation, in a reduced-to-oxidized path most probably. Another important parameter is whether or not water is present in the primordial magma ocean. Indeed, we now have more and more lines of evidences showing that the volatile elements, especially water, arrived during accretion and therefore during the core-mantle segregation, which means that water can have an effect on the latter phenomenon. Considering this hypothesis, we performed several high pressure-high temperature experiments which allowed us to model the formation of the core under hydrous conditions. These experiments demonstrated that water has a significant effect on the redox state evolution of planetary mantles. We use this redox evolution to constrain models of planetary accretions, based on a mix of EH and CI chondrites, showing a good agreement with models based on isotopic data. The output of these models is the maximum initial concentration in water on the Earth (1.2 -1.8 %wt) and on Mars (2.5-3.5 %wt). Furthermore, these experiments showed a lithophile behavior (i.e. which has affinities with silicated phases) of hydrogen at high pressures, contrary to previous studies. Therefore, the difference between high initial concentrations in water yielded by our accretion models and the estimated actual concentrations on the Earth and Mars (2000 ppm and 200 ppm, respectively) cannot be explained by a hydrogen reservoir in the core. Finally, to improve the models of core-mantle segregation, we showed by numerical simulations the important effect of the magma ocean viscosity on the equilibrium between planetary mantles and cores. it lead us to reevaluate the models of accretion based on experimental data, especially the maximum extent of magma oceans. The evolution of the magma ocean viscosity has therefore significant implications on the final composition of planetary cores (for instance on the sulfur, oxygen and silicon content of the Earth’s and Mars’ core).

Um einen besseren Zugang zum Verständnis struktureller Eigenschaften von den ternären Verbindungen des Systems Yb–Pd–Ga zu bekommen, wurden zunächst die Ordnungs- und Unordnungsbeziehungen sowie die chemische Bindung in den Kristallstrukturen binärer Pd–Ga- bzw. Yb–Ga-Verbindungen analysiert. Im Rahmen der phasenanalytischen Untersuchungen des binären Systems Yb–Ga konnte eine neue Verbindung charakterisiert werden (Ytterbiumpentagallid). Für den galliumreichen Teil des ternären Phasendiagramms Yb–Pd–Ga wurde ein isothermer Schnitt bei 600 °C erstellt (&amp;gt; 50 At.-% Ga). Die Homogenitätsbereiche der untersuchten Verbindungen wurden metallographisch bzw. röntgenographisch bestimmt. Die Kristallstrukturen wurden aus Röntgen-Einkristalldaten bestimmt. In den Kristallstrukturen wurden drei unterschiedliche Arten von Unordnung beobachtet (Substitutionsunordnung, Symmetrie-Brechung, Positionsunordnung). Für eine Reihe von Verbindungen des Systems Yb–Pd–Ga wurde der elektronische Zustand von Yb bestimmt. Dies gelang mit Hilfe von Messungen der magnetischen Suszeptibilität bzw. mit der Röntgen-Absorptionsnahkantenspektroskopie.