Quantum Mechanics Insight into the Microwave Nucleation of SrTiO3 Nanospheres

An extensive investigation of strontium titanate, SrTiO3 (STO), nanospheres synthesized via a microwave-assisted hydrothermal (MAH) method has been conducted to gain a better insight into thermodynamic, kinetic, and reaction phenomena involved in STO nucleation and crystal growth processes. To this end, quantum chemical modeling based on the density functional theory and periodic super cell models were done. Several experimental techniques were employed to get a deep characterization of structural and optical features of STO nanospheres. A possible formation mechanism was proposed, based on dehydration of titanium and strontium clusters followed by mesoscale transformation and a self-assembly process along an oriented attachment mechanism resulting in spherical like shape. Raman and XANES analysis renders a noncentrosymmetric environment for the octahedral titanium, while infrared and first order Raman modes reveal OH groups which are unsystematically incorporated into uncoordinated superficial sites. These results seem to indicate that the key component is the presence of distorted TiO6 clusters to engender a luminescence property. Analysis of band structure, density Of states, and charge map shows that there is a close relationship among local broken symmetry, polarization, and energy split of the 3d orbitals of titanium. The interplay among these electronic and structural features provides necessary conditions to evaluate its luminescent properties under two energy excitation.

Bounds on the density of sources of ultra-high energy cosmic rays from the Pierre Auger Observatory

We derive lower bounds on the density of sources of ultra-high energy cosmic rays from the lack of significant clustering in the arrival directions of the highest energy events detected at the Pierre Auger Observatory. The density of uniformly distributed sources of equal intrinsic intensity was found to be larger than ~(0.06 - 5) × '10 POT. -4' 'Mpc POT. -3' at 95% CL, depending on the magnitude of the magnetic deflections. Similar bounds, in the range (0.2 - 7) × '10 POT. -4' 'Mpc POT. -3', were obtained for sources following the local matter distribution.

Comparison of model potentials for molecular dynamics simulation of crystalline silica

Simulationen von SiO2 mit dem von van Beest, Kramer und vanSanten (BKS) entwickelten Paarpotenzial erzeugen vielezufriedenstellende Ergebnisse, aber auch charakteristischeSchwachstellen. In dieser Arbeit wird das BKS-Potenzial mitzwei kürzlich vorgeschlagenen Potenzialen verglichen, dieeffektiv Mehrteilchen-Wechselwirkungen beinhalten. Der ersteAnsatz erlaubt dazu fluktuierende Ladungen, der zweiteinduzierbare Polarisierungen auf den Sauerstoffatomen. Die untersuchten Schwachstellen des BKS Potenzialsbeinhalten das Verhältnis der zwei Gitterkonstanten a und cim Quarzübergang, das von BKS falsch beschrieben wird.Cristobalit und Tridymit erscheinen instabil mit BKS.Weiterhin zeigt die BKS-Zustandsdichte charakteristischeAbweichungen von der wahren Zustandsdichte. DerÜbergangsdruck für den Stishovit I-II Übergang wird deutlichüberschätzt. Das Fluktuierende-Ladungs-Modell verbesserteinige der genannten Punkte, reproduziert aber viele andereEigenschaften schlechter als BKS. DasFluktierende-Dipol-Modell dagegen behebt alle genanntenArtefakte. Zusätzlich wird der druckinduzierte Phasenübergang imalpha-Quarz untersucht. Alle Potentiale finden die selbeStruktur für Quarz II. Bei anschliessender Dekompressionerzeugt BKS eine weitere Phase, während die beiden anderenPotentiale wieder zum alpha-Quarz zurückkehren. Weiterhinwerden zwei Methoden entwickelt, um die piezoelektrischenKonstanten bei konstantem Druck zu bestimmen. Die Ergebnissegeben Hinweise auf eine möglicherweisenicht-elektrostatische Natur der Polarisierungen imFluktuierende-Dipole-Modell. Mit dieser Interpretation scheint das Fluktuierende-DipolPotential alle verfügbaren experimentellen Daten am bestenvon allen drei untersuchten Ansätzen zu reproduzieren.

Numerical study of graphene as a channel material for field-effect transistors

Graphene excellent properties make it a promising candidate for building future nanoelectronic devices. Nevertheless, the absence of an energy gap is an open problem for the transistor application. In this thesis, graphene nanoribbons and pattern-hydrogenated graphene, two alternatives for inducing an energy gap in graphene, are investigated by means of numerical simulations. A tight-binding NEGF code is developed for the simulation of GNR-FETs. To speed up the simulations, the non-parabolic effective mass model and the mode-space tight-binding method are developed. The code is used for simulation studies of both conventional and tunneling FETs. The simulations show the great potential of conventional narrow GNR-FETs, but highlight at the same time the leakage problems in the off-state due to various tunneling mechanisms. The leakage problems become more severe as the width of the devices is made larger, and thus the band gap smaller, resulting in a poor on/off current ratio. The tunneling FET architecture can partially solve these problems thanks to the improved subthreshold slope; however, it is also shown that edge roughness, unless well controlled, can have a detrimental effect in the off-state performance. In the second part of this thesis, pattern-hydrogenated graphene is simulated by means of a tight-binding model. A realistic model for patterned hydrogenation, including disorder, is developed. The model is validated by direct comparison of the momentum-energy resolved density of states with the experimental angle-resolved photoemission spectroscopy. The scaling of the energy gap and the localization length on the parameters defining the pattern geometry is also presented. The results suggest that a substantial transport gap can be attainable with experimentally achievable hydrogen concentration.

Development of empirical potentials for amorphous silica

Development of empirical potentials for amorphous silica Amorphous silica (SiO2) is of great importance in geoscience and mineralogy as well as a raw material in glass industry. Its structure is characterized as a disordered continuous network of SiO4 tetrahedra. Many efforts have been undertaken to understand the microscopic properties of silica by classical molecular dynamics (MD) simulations. In this method the interatomic interactions are modeled by an effective potential that does not take explicitely into account the electronic degrees of freedom. In this work, we propose a new methodology to parameterize such a potential for silica using ab initio simulations, namely Car-Parrinello (CP) method [Phys. Rev. Lett. 55, 2471 (1985)]. The new potential proposed is compared to the BKS potential [Phys. Rev. Lett. 64, 1955 (1990)] that is considered as the benchmark potential for silica. First, CP simulations have been performed on a liquid silica sample at 3600 K. The structural features so obtained have been compared to the ones predicted by the classical BKS potential. Regarding the bond lengths the BKS tends to underestimate the Si-O bond whereas the Si-Si bond is overestimated. The inter-tetrahedral angular distribution functions are also not well described by the BKS potential. The corresponding mean value of theSiOSi angle is found to be ≃ 147◦, while the CP yields to aSiOSi angle centered around 135◦. Our aim is to fit a classical Born-Mayer/Coulomb pair potential using ab initio calculations. To this end, we use the force-matching method proposed by Ercolessi and Adams [Europhys. Lett. 26, 583 (1994)]. The CP configurations and their corresponding interatomic forces have been considered for a least square fitting procedure. The classical MD simulations with the resulting potential have lead to a structure that is very different from the CP one. Therefore, a different fitting criterion based on the CP partial pair correlation functions was applied. Using this approach the resulting potential shows a better agreement with the CP data than the BKS ones: pair correlation functions, angular distribution functions, structure factors, density of states and pressure/density were improved. At low temperature, the diffusion coefficients appear to be three times higher than those predicted by the BKS model, however showing a similar temperature dependence. Calculations have also been carried out on crystalline samples in order to check the transferability of the potential. The equilibrium geometry as well as the elastic constants of α-quartz at 0 K are well described by our new potential although the crystalline phases have not been considered for the parameterization. We have developed a new potential for silica which represents an improvement over the pair potentials class proposed so far. Furthermore, the fitting methodology that has been developed in this work can be applied to other network forming systems such as germania as well as mixtures of SiO2 with other oxides (e.g. Al2O3, K2O, Na2O).

Magnetic tunneling junctions with the Heusler compound Co 2 Cr 0.6 Fe 0.4 Al

Materialen mit sehr hoher Spinpolarisation werden für Anwendungen im Bereich der Spin-Elektronik benötigt. Deshalb werden große Forschungsanstrengungen zur Untersuchung der Eigenschaften von Verbindungen mit potentiell halbmetallischem Charakter, d. h.mit 100% Spinpolarisation, unternommen. In halbmetallischen Verbindungen, erwartet man eine Lücke in der Zustandsdichte an der Fermi Energie für Ladungsträger einer Spinrichtung, wahrend die Ladungsträger mit der anderen Spinrichtung sich metallisch verhalten. Eine Konsequenz davon ist, dass ein Strom, der durch solche Verbindung fließt, voll spinpolarisiert ist. Die hohe Curie-Temperatur Tc (800 K) und der theoretisch vorhergesagte halbmetallische Charakter machen Co2Cr0.6Fe0.4Al (CCFA) zu einem guten Kandidaten für Spintronik-Anwendungen wie magnetische Tunnelkontakte (MTJs = Magnetic Tunneling Junctions). In dieser Arbeit werden die Ergebnisse der Untersuchung der elektronischen und strukturellen Eigenschaften von dünnen CCFA Schichten dargestellt. Diese Schichten wurden in MTJs integriert und der Tunnel-Magnetowiderstands-Effekt untersucht. Hauptziele waren die Messung der Spinpolarisation und Untersuchungen der elektronischen Struktur von CCFA. Der Einfluss verschiedener Depositionsparameter auf die Eigenschaften der Schichten, speziell auf der Oberflächenordnung und damit letztlich auf den Tunnel-Magnetowiderstand (TMR), wurde bestimmt. Epitaktische d¨unne CCFA Schichten mit zwei verschiedenen Wachstumsrichtungen wurden auf verschiedene Substrate und Pufferschichten deponiert. Ein Temperverfahren wurde eingesetzt um die strukturelle Eigenschaften der dünnen Schichten zu verbessern. Für die MTJs wurde Al2O3 als Barrierenmaterial verwendet und Co als Gegenelektrode gewählt. Die Mehrschicht-Systeme wurden in Mesa-Geometrie mit lithographischen Methoden strukturiert. Eine maximal Jullière Spinpolarisation von 54% wurde an Tunnelkontakte mit epitaktischen CCFA Schichten gemessen. Ein starker Einfluss der Tempernbedingungen auf dem TMR wurde festgestellt. Eine Erhörung des TMR wurde mit einer Verbesserung der Oberflächenordung der CCFA Schichten korreliert. Spektroskopische Messungen wurden an den MTJs durchgeführt. Diesen Messungen liefern Hinweise auf inelastische Elektron-Magnon und Elektron-Phonon Stossprozesse an den Grenzflächen. Einige der beobachteten Strukturen konnten mit der berechneten elektronischen Struktur von CCFA korreliert worden.

Electrical spectroscopy of rubrene bulk and thin film crystals

One of the most diffused electronic device is the field effect transistor (FET), contained in number of billions in each electronic device. Organic optoelectronics is an emerging field that exploits the unique properties of conjugated organic materials to develop new applications that require a combination of performance, low cost and processability. Organic single crystals are the material with best performances and purity among the variety of different form of organic semiconductors. This thesis is focused on electrical and optical characterization of Rubrene single crystal bulk and thin films. Rubrene bulk is well known but for the first time we studied thin films. The first Current-voltage characterization has been performed for the first time on three Rubrene thin films with three different thickness to extract the charge carriers mobility and to assess its crystalline structure. As results we see that mobility increase with thickness. Field effect transistor based on Rubrene thin films on $SiO_2$ have been characterize by current-voltage (I-V) analyses (at several temperatures) and reveals a hopping conduction. Hopping behavior probably is due to the lattice mismatch with the substrate or intrinsic defectivity of the thin films. To understand effects of contact resistance we tested thin films with the Transmission Line Method (TLM) method. The TLM method revealeds that contact resistance is negligible but evidenced a Schottky behavior in a limited but well determined range of T. To avoid this effect we carried out annealing treatment after the electrode evaporation iswe performed a compete I-V characterization as a function of in temperature to extract the electronic density of states (DOS) distribution through the Space Charge Limited Current (SCLC) method. The results show a DOS with an exponential trenddistribution, as expected. The measured mobility of thin films is about 0.1cm^2/Vs and it increases with the film thickness. Further studies are necessary to investigate the reason and improve performances. From photocurrent spectrum we calculated an Eg of about 2.2eV and both thin films and bulk have a good crystal order. Further measurement are necessary to solve some open problems

Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations.rnThe aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co2FeAl0.3Si0.7 and Co2MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultra-violet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy.rnHeusler compounds are prepared as thin films by RF-sputtering in an ultra-high vacuum system. rnFor the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co2FeAl0.3Si0.7 and Co2MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L21) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5% below from the theoretically predicted.rnBy ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on brodening effects of DOS features. Improving order resulted in better defined ARUPS features.rnTunneling magnetoresistance measurements of Co2FeAl0.3Si0.7 and Co2MnGa based MTJ’s result in a Co2FeAl0.3Si0.7 spin polarization of 44%, which is the highest experimentally obtained value for this compound, although it is lower than the 100% predicted. For Co2MnGa no high TMR was achieved.rnUnpolarized tunneling spectroscopy reveals contribution of interface states close to the Fermi energy. Additionally magnon excitations due to magnetic impurities at the interface are observed. Such contributions can be the reason of a reduced TMR compared to the theoretical predictions. Nevertheless, for energies close to the Fermi energy and for Co2MnGa, the validity of the band structure calculations is demonstrated with this technique as well.

Electronic structure and physical properties of Heusler compounds for thermoelectric and spintronic applications

This thesis focuses on synthesis as well as investigations of the electronic structure and properties of Heusler compounds for spintronic and thermoelectric applications.rnThe first part reports on the electronic and crystal structure as well as the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co2MnGe. The crystalline structure was examined in detail by extended X-ray absorption fine structure spectroscopy and anomalous X-ray diffraction. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab-initio calculations. Transport measurements and hard X-ray photoelectron spectroscopy (HAXPES) were performed to explain the electronic structure of the compound.rnA major part of the thesis deals with a systematical investigation of Heusler compounds for thermoelectric applications. Few studies have been reported on thermoelectric properties of p-type Heusler compounds. Therefore, this thesis focuses on the search for new p-type Heusler compounds with high thermoelectric efficiency. The substitutional series NiTi1−xMxSn and CoTi1−xMxSb (where M = Sc, V and 0 ≤ x ≤ 0.2) were synthesized and investigated theoretically and experimentally with respect to electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler compound. The pure compounds showed n-type behavior, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 μV/K (at 350 K) was obtained for NiTi0.26Sc0.04Zr0.35Hf0.35Sn, which is one of the highest values for p-type thermoelectric compounds based on Heusler alloys up to now. HAXPES valence band measurement show massive in gap states for the parent compounds NiTiSn, CoTiSb and NiTi0.3Zr0.35Hf0.35Sn. This proves that the electronic states close to the Fermi energy play a key role for the behavior of the transport properties. Furthermore, the electronic structure of the gapless Heusler compounds PtYSb, PtLaBi and PtLuSb were investigated by bulk sensitive HAXPES. The linear behavior of the spectra close to εF proves the bulk origin of Dirac-cone type density of states. Furthermore, a systematic study on the optical and transport properties of PtYSb is presented. The compound exhibits promising thermoelectric properties with a high figure of merit (ZT = 0.2) and a Hall mobility μh of 300 cm2/Vs at 350 K.rnThe last part of this thesis describes the linear dichroism in angular-resolved photoemission from the valence band of NiTi0.9Sc0.1Sn and NiMnSb. High resolution photoelectron spectroscopy was performed with an excitation energy of hν = 7.938 keV. The linear polarization of the photons was changed using an in-vacuum diamond phase retarder. Noticeable linear dichroism is found in the valence bands and this allows for a symmetry analysis of the contributing states. The differences in the spectra are found to be caused by symmetry dependent angular asymmetry parameters, and these occur even in polycrystalline samples without preferential crystallographic orientation.rnIn summary, Heusler compounds with 1:1:1 and 2:1:1 stoichiometry were synthesized and examined by chemical and physical methods. Overall, this thesis shows that the combination of first-principle calculations, transport measurements and high resolution high energy photoelectron spectroscopy analysis is a very powerful tool for the design and development of new materials for a wide range of applications from spintronic applications to thermoelectric applications.rn

Spectroscopic investigations of functional bulk and thin film Heusler alloys

Functional and smart materials have gained large scientific and practical interest in current research and development. The Heusler alloys form an important class of functional materials used in spintronics, thermoelectrics, and for shape memory alloy applications. An important aspect of functional materials is the adaptability of their physical properties. In this work functional polycrystalline bulk and epitaxial thin film Heusler alloys are characterized by means of spectroscopic investigation methods, X-ray magnetic circular dichroism (XMCD) and energy dispersive X-ray analysis (EDX). With EDX the homogeneity of the samples is studied extensively. For some cases of quaternary compounds, for example Co2(MnxTi1−x)Sn and Co2(Mn0.5Dy0.5)Sn, an interesting phase separation in two nearly pure ternary Heusler phases occurs. For these samples the phase separation leads to an improvement of thermoelectric properties. XMCD as the main investigation method was used to study Co2TiZ (Z = Si, Sn, and Sb), Co2(MnxTi1−x)Si, Co2(MnxTi1−x)Ge, Co2Mn(Ga1−xGex), Co2FeAl, Mn2VAl, and Ni2MnGa Heusler compounds. The element-specific magnetic moments are calculated. Also, the spin-resolved unoccupied density of states is determined, for example giving hints for half-metallic ferromagnetism for some Co-based compounds. The systematic change of the magnetic moments and the shift of the Fermi energy is a proof that Heusler alloys are suitable for a controlled tailoring of physical properties. The comparison of the experimental results with theoretical predictions improves the understanding of complex materials needed to optimize functional Heusler alloys.

Quantenchemische Behandlung von elektronischem Energietransfer

Im Rahmen dieser Dissertation wurden quantenchemische Untersuchungen zum Phänomen des elektronischen Energietransfers durchgeführt. Zum einen wurden theoretische Modelle zur Berücksichtigung temperaturabhängiger Elektron-Phonon-Kopplung in vibronischen Spektren ausgearbeitet und numerischen Tests unterzogen. Zum anderen erfolgte die Bestimmung molekularer Eigenschaften bichromophorer Systeme unter Anwendung etablierter Rechenmethoden. Im Fokus stehen das Zusammenspiel elektronischer Kopplung und statischer Unordnung sowie Energietransferzeiten und der Einfluss molekularer Brücken in Dimeren auf die Kopplung. Da sich elektronischer Energietransfer spektroskopisch nachweisen lässt, wurden temperaturabhängige Simulationen der Linienform von vibronischen Übergängen, die an ein Wärmebad ankoppeln, durchgeführt. Die erforderliche Antwortfunktion zur Bestimmung der spektralen Linienform kann aus einer Kumulantenentwicklung und alternativ aus der Multi-Level Redfieldtheorie abgeleitet werden. Statt der genäherten Schwingungsstruktur des Brownschen Oszillatormodells wurde eine explizit berechnete Zustandsdichte als Ausgangspunkt verwendet. Sowohl reine Elektron-Phonon- als auch Schwingung-Phonon-Kopplung werden für verschiedene Spektraldichten der Badmoden diskutiert. Im Zuge eines Kooperationsprojekts führten wir Untersuchungen zur elektronischen Kopplung an einer homologen Reihe von Rylendimeren mit unterschiedlichen Brückenlängen durch. Zu diesem Zweck wurden Ergebnisse aus Tieftemperatureinzelmolekülmessungen und quantenchemischen Berechnungen auf Grundlage des vibronischen Kopplungsmodells herangezogen und ausgewertet. Die untersuchten Dimere zeigen einen Übergang vom Grenzfall starker Kopplung hin zu schwacher Kopplung und die mittleren Energietransferzeiten konnten in guter Übereinstimmung mit experimentellen Messwerten berechnet werden. Da eine molekulare Brücke zwischen Donor- und Akzeptoreinheit die elektronische Kopplung modifiziert, kann sie sich störend auf experimentelle Messungen auswirken. Daher wurde untersucht, ob das interchromophore Kopplungsverhalten vorwiegend durch die Polarisierbarkeit des verbrückenden Elements oder durch bindungsvermittelte Wechselwirkungen beeinflusst wird und welche Brückentypen sich folglich für experimentelle Studien eignen. Sämtliche untersuchten Brückenelemente führten zu einer Vergrößerung der elektronischen Kopplung und die Kopplungsstärke wurde maßgeblich durch brückenvermittelte Wechselwirkungen bestimmt.

Temperatur- und ortsabhängige Zustandsdichte des organischen Supraleiters Kappa-(BEDT-TTF) 2 Cu[N(CN) 2]Br

Im Rahmen dieser Arbeit wurde die temperatur- und ortsabhängige Zustandsdichte des organischen Supraleiters kappa-(BEDT-TTF)2Cu[N(CN)2]Br mit Rastertunnelspektroskopie bei tiefen Temperaturen untersucht.rnZusätzlich zur bereits bekannten supraleitenden Energielücke wird dabei eine logarithmische Unterdrückung der Zustandsdichte an der Fermikante beobachtet, die auch oberhalb der kritischen Temperatur erhalten bleibt. In der vorliegenden Arbeit wird gezeigt, dass sich dieses Verhalten durch ein für ungeordnete elektronische Systeme entwickeltes Modell unter Berücksichtigung von Coulomb-Wechselwirkungen beschreiben lässt. Die daraus resultierenden Fluktuationen der elektronischen Struktur führen zu einer Verbreiterung der gemessenen supraleitenden Energielücke, die sich durch sehr kleine Kohärenzmaxima im entsprechenden Quasiteilchenanregungsspektrum äußert. Dieses Verhalten wurde bereits beobachtet, konnte jedoch bisher nicht erklärt werden. Die theoretische Beschreibung der logarithmischen Unterdrückung trägt somit zusätzlich zum Verständnis des supraleitenden Beitrags bei, sodass die gesamte Zustandsdichte vollständig beschrieben werden kann. Die Analyse der gemessenen supraleitenden Energielücke wurde für verschiedene Symmetrien des Ordnungsparameters durchgeführt, wobei die beste Übereinstimmung für die Annahme einer d-wellenartigen Symmetrie mit zwei unterschiedlich stark ausgeprägten Energielücken gefunden wurde. Der Paarbildungsmechanismus, der zur Bindung zweier Elektronen zu einem Cooper-Paar führt, kann mit einer $d$-wellenartigen Symmetrie nicht durch die in konventionellen Supraleitern gefundene Elektron-Phonon-Kopplung erklärt werden. Stattdessen wird in Analogie zur Hochtemperatur-Supraleitung eine durch antiferromagnetische Spin-Wechselwirkungen induzierte Kopplung der Elektronen vermutet. Dies wird zum einen durch die oberhalb der kritischen Temperatur auftretende, zweite Energielücke und zum anderen durch die zwischen 4,66 und 5,28 liegende Kopplungsstärke 2Delta/(kB Tc) unterstützt, die deutlich größer als für konventionelle Supraleiter mit Elektron-Phonon-Kopplung ist.

The Effect of Various Electrode Microstructure Parameters on the Effective Conductivity and Three-Phase Boundary Density of Infiltrated SOFC Electrodes

Solid oxide fuel cell (SOFC) technology has the potential to be a significant player in our future energy technology repertoire based on its ability to convert chemical energy into electrical energy. Infiltrated SOFCs, in particular, have demonstrated improved performance and at lower cost than traditional SOFCs. An infiltrated electrode comprises porous ceramic scaffolding (typically constructed from the oxygen ion conducting material) that is infiltrated with electron conducting and catalytic particles. Two important SOFC electrode properties are effective conductivity and three phase boundary density (TPB). Researchers study these electrode properties separately, and fail to recognize them as competing properties. This thesis aims to (1) develop a method to model the TPB density and use it to determine the effect of porosity, scaffolding particle size, and pore former size on TPB density as well as to (2) compare the effect of porosity, scaffolding particle size, and pore former size on TPB density and effective conductivity to determine a desired set of parameters for infiltrated SOFC electrode performance. A computational model was used to study the effect of microstructure parameters on the effective conductivity and TPB density of the infiltrated SOFC electrode. From this study, effective conductivity and TPB density are determined to be competing properties of SOFC electrodes. Increased porosity, scaffolding particle size, and pore former particle size increase the effective conductivity for a given infiltrate loading above percolation threshold. Increased scaffolding particle size and pore former size ratio, however, decreases the TPB density. The maximum TPB density is achievable between porosities of 45% and 60%. The effect of microstructure parameters are more prominent at low loading with scaffolding particle size being the most significant factor and pore former size ratio being the least significant factor.