Nickel-Silicidphasen wurden auf neuen Synthesewegen bei relativ niedrigen Temperaturen und kurzen Reaktionszeiten präpariert. Die Belastung von dispersem Metall mit Siliciumtetrachlorid liefert Produkte, die mit den thermodynamischen Berechnungen korrelieren. Bei der direkten Umsetzung von Nickelhalogeniden mit Silicium beeinflussen die Versuchsbedingungen wesentlich die Zusammensetzung der resultierenden Phasengemische. Durch Temperungen reduziert sich der Bestand an Silicidphasen. Die Umsetzung von Nickelchlorid und Silicium gelang erstmals auch in einer KCl/LiCl-Salzschmelze als Reaktionsmedium, wodurch sich thermodynamisch vorhersagbare Silicidphasen erhalten lassen. In einigen Fällen deuten die Ergebnisse auf die Bildung halogenhaltiger, bei Raumtemperatur metastabiler Silicidphasen hin. Zum Reaktionsmechanismus werden zwei über die Oxidationsstufe +2 des Siliciums verlaufende Routen diskutiert.

The main motivation of this work was the preparation and characterization of novel compounds in the ternary systems RE–T–C with T = Cr, Fe and Ru with a special focus on compounds containing C2n- and C3m- or mixed C and C2n- as structural units. This would allow to investigate the applicability of the concept of complex anions to this class of materials.

Im Rahmen dieser Arbeit wurden thermodynamische Modellationen, Synthesen und Strukturuntersuchungen zu Lanthanoidpolysulfiden und den selenärmeren Lanthanoid-polyseleniden durchgeführt. Bereits bekannte thermodynamische Daten der Lanthanoidpolysulfide, welche durch Gesamtdruckmessungen ermittelt wurden, konnten genutzt werden, um neue Synthesewege zur Darstellung der Lanthanoidpolysulfide thermodynamisch zu modellieren. Im Rahmen dieser Modellierungen wurde für Praseodym exemplarisch gezeigt, dass ein chemischer Gasphasentransport der Polysulfide unter Zugabe von Br2(l) und unter der Ausbildung des Transportmittels SBr2(g) möglich ist. Des Weiteren konnte die Synthese der Verbindungen LnS1.9 (Ln = La – Nd, Gd) unter Verwendung von HgS als Sulfiddonor durchgeführt und anhand der entwickelten elektrochemischen Spannungsreihe anorganischer sulfidischer Festkörper sowie weiterführender thermodynamischer Rechnungen rationalisiert werden. Die durch thermodynamische Rechnungen optimierten Synthesen lieferten Kristalle guter bis hervorragender Qualität, welche durch anschließende Röntgen¬beugungsexperimente charakterisiert wurden. Anhand dieser Daten konnten die Kristallstrukturen einer Vielzahl von Lanthanoidpolychalkogeniden LnQ2–δ (Ln = La – Ho, Y; Q = S, Se; 0 £  £ 0.15) gelöst und verfeinert werden. Die Strukturtypen, welche im Rahmen dieser Arbeit für die Lanthanoidpolychalkogenide gefunden wurden, sind der CeSe2-Typ, der CeSe1.9-Typ, eine niedersymmetrische Form des GdSe1.875-Typs und eine inkommensurabel modulierte Variante des PrSe1.85-Typs. Da es sich bei allen beschriebenen Verbindungen um Überstrukturen des ZrSSi-Typs handelt, wurden zur Veranschaulichung dieser Tatsache Bärnighausen-Stammbäume für die gefundenen Strukturtypen aufgestellt. Anhand dieser Stammbäume wurde illustriert, wie sich die Atomlagen der niedersymmetrischen Überstrukturen aus denen des hochsymmetrischen Aristotyps ableiten lassen.

In den Untersuchungen zur Phasenbildung und -stabilität im System Na2SO4 - CaSO4 - H2O wurden die bisher existierenden Phasendiagramme für das wasserfreie System Na2SO4 - CaSO4 korrigiert. Metastabile Mischkristalle wurden bezüglich ihrer Existenzgebiete und Zusammensetzungen charakterisiert. Für den im wässrigen System stabil auftretenden Glauberit, Na2SO4 . CaSO4, wurde die Löslichkeitskonstante bis 250°C bestimmt und ist ab 100°C kleiner als bisher angenommen wurde. Zur Bestimmung der Löslichkeitskonstante wurde die Temperaturabhängigkeit der Freien Standardreaktionsenthalpie für die Zersetzung des Glauberits ermittelt. Dazu wurden die Cp-Funktionen für die an der Reaktion beteiligten Phasen Glauberit und Anhydrit, CaSO4, über Wärmekapazitätsmessungen bis 510°C bestimmt. Eine weitere Möglichkeit zur Bestimmung der Freien Standardreaktionsenthalpie durch die Ermittlung der thermodynamischen Aktivität von Na2SO4 in der Hochtemperaturmischkristallphase mit EMK-Messungen an Festkörperelektroden wurde aufgezeigt. Für das im System Na2SO4 - CaSO4 - H2O metastabile auftretende Natriumpentasalz, Na2SO4 . 5 CaSO4 . 3 H2O, wurde eine Einkristallstrukturanalyse durchgeführt und die strukturelle Verwandtschaft zum Calciumsulfat-Halbhydrtat, CaSO4 . 0,5 H2O, aufgeklärt, sowie die Bildungsbedingungen charakterisiert.

Borophosphates are intermediate compounds of systems MxOy–B2O3–P2O5–(H2O) (M = main group or transition metal) which contain complex anionic structures built of interconnected trigonal–planar BO3 and / or BO4 and PO4 groups and their partially protonated species. The main objective of the present work was to synthesize, characterize and to study the properties of new selected 3d transition metal borophosphates. The selected four elements are scandium (Sc), iron (Fe), cobalt (Co) and nickel (Ni) due to their interesting contributions to borophosphate structural chemistry. The mild hydrothermal method was employed for the syntheses. During the investigation of borophosphates containing alkali–metals and scandium, the following three compounds were prepared and structurally characterized: MISc[BP2O8(OH)] (MI = K, Rb), CsSc[B2P3O11(OH)3] The anionic partial structure of MISc[BP2O8(OH)] (MI = K, Rb) consists of the well known open–branched four–membered rings of alternating borate and phosphate tetrahedra (a loop–branched hexamer with B : P = 1 : 2). The anionic partial structure of CsSc[B2P3O11(OH)3] represents the new type of oligomer containing boron in three– and four– fold coordination (B : P = 2 : 3). This is also the first time that a BO3 group is not only linked to borate species but also to a phosphate tetrahedron. This kind of oligomer was already predicted for borates but was never observed. By this, CsSc[B2P3O11(OH)3] is a special compound with regard to the structural building principles of borates and borophosphates. The significant differences in the crystal structures of MISc[BP2O8(OH)] (MI = K, Rb) and CsSc[B2P3O11(OH)3] may be due to the higher coordination number of cesium. Thermal treatment (up to 1000 ºC) of these compounds resulted in white crystalline products containing new phases with unknown crystal structures. Besides the discovery of alkali–metal scandium borophosphates, five new alkali metal scandium hydrogenphosphates were synthesized and structurally characterized: Li2Sc[(PO4)(HPO4)], MISc(HPO4)2 (MI = K, Rb, Cs, NH4) It was already predicted that open framework scandium phosphates should be isotypes of the respective indium phosphates. It was also stated that there should be a whole family of scandium hydrogenphosphates as we were able to confirm with the five novel compounds. Our systematic study reveals the structural changes of the anionic partial frameworks with increasing ionic radii of the alkali–metal ion. With respect to the M―T connections (M = six coordinated central metal atom, T = four coordinated phosphorous atom) the channel size increases from 8–membered rings in Li2Sc[(PO4)(HPO4)] to 12–membered rings in MISc(HPO4)2 (MI = K, Rb, Cs, NH4). KSc(HPO4)2 exhibits a new structure type in the family of monohydrogenphosphates with the general formula MIMIII(HPO4)2. This provides further evidence that scandium is a suitable element for the synthesis of framework structures with different channel sizes. The observation that in analogy to MISc(HPO4)2 (MI = Rb, Cs, NH4) a compound exists where the MI site is replaced by H3O+ gives rise to the hope that ion exchange properties could be of interest in this class of compounds. In addition, the possible existence of further modifications (as reported for the element–combinations RbV, NH4V, RbFe, and CsIn) shoud be investigated by thermoanalytical and X–ray methods. The extensive studies on borophosphate containing the transition metals Fe, Co, Ni together with alkaline earth–metals (Mg, Ca, Sr, Ba) led to the preparation of 13 compounds containing the combination of two different divalent M1IIM2II ions: CaM2II[BP2O7(OH)3] (M2II = Fe, Ni), BaM2II[BP2O8(OH)] (M2II = Fe, Co), SrFe[BP2O8(OH)2], CaCo(H2O)[BP2O8(OH)]•H2O, M1II0.5M2II(H2O)2[BP2O8]•H2O (M1II0.5 = Ca, Sr, Ba; M2II = Fe, Co, Ni) The anionic partial structure of CaM2II[BP2O7(OH)3] (M2II = Fe, Ni) consists of a tetrahedral triple [BP2O7(OH)3]4-, built from a central (HO)2BO2 tetrahedron sharing common vertices with two (H0.5)OPO3 tetrahedra. The complex anions in the crystal structure of BaM2II[BP2O8(OH)] (M2II = Fe, Co) comprises open–branched four–membered rings, [B2P4O16(OH)2]8-, which are formed by alternating (HO)BO3 and PO4 tetrahedra sharing common corners with two additional PO4 branches. The interconnection of these complex anions with M2II coordination octahedra (M2II = Fe, Co, Ni) by sharing common corners results in overall three–dimensional frameworks which contain channels filled with the M1II ions (M1II = Ca, Ba). The anionic partial structure of SrFe[BP2O8(OH)2] is built from a central (HO)2BO2 tetrahedron sharing common vertices with two PO4 tetrahedra. Surprisingly, SrFe[BP2O8(OH)2] represents the first example in the structural chemistry of borophosphates where the charge of the anionic partial structure is balanced by a divalent and a trivalent species (MIIMIII). Although being a member of the M1IIM2II[BP2O8(OH)] family the crystal structure of CaCo(H2O)[BP2O8(OH)]•H2O is different. Interestingly, this is the first case in the borophosphate structural chemistry where dimers of cobalt coordination octahedra together with borophosphate oligomers form a (two–dimensional) layered structure. The helical borophosphates M1II0.5M2II(H2O)2[BP2O8]•H2O (M1II0.5 = Ca, Sr, Ba; M2II = Fe, Co, Ni) contain one–dimensional infinite loop–branched borophosphate helices built of alternatively distorted borate and phosphate tetrahedra. Up to now, the group of compounds with 1[BP2O8]3– helical chain anions has been synthesized only in combination with different cations MIMII and MIII (MI = Li, Na, K; MII = Mg, Mn, Fe, Co, Ni, Zn; MIII = Sc, In, Fe). The systematic investigation on helical borophosphates of transition metals (Fe, Co, Ni) and alkaline–earth metals showed that it is also possible to accommodate divalent metal cations within the structure without disturbing the anionic partial structure. It was not possible to find the completely ordered structural model for the compounds M1II0.5M2II(H2O)2[BP2O8]•H2O (M1II0.5 = Ca, Sr, Ba; M2II = Co) but the substructure presented shows good agreement with the ordered known helical borophosphate compounds. Interestingly, it was also possible to judge the “kind of superstructure” against the crystal morphology. Syntheses of one of the few examples of borophosphates containing layered anionic partial structures (63 net topology) containing transition metal cations (Fe, Co, Ni) was realized with 6 isotypic compounds: MII(H2O)2[B2P2O8(OH)2]•H2O (MII = Fe, Co, Ni, Ni0.5Co0.5, Ni0.8Zn0.2, Ni0.5Mg0.5) The compounds MII(H2O)2[B2P2O8(OH)2]•H2O (MII = Fe, Co, Ni) adopt the structure type of Mg(H2O)2[B2P2O8(OH)2]•H2O characterized by a two–dimensional borophosphate anion. Substitution on the transition metal sites was shown to be possible (Ni0.5Co0.5) realized for this structure type. With the synthesis of Ni0.8Zn0.2(H2O)2[B2P2O8(OH)2]•H2O and Ni0.5Mg0.5(H2O)2[B2P2O8(OH)2]•H2O it was also proved that magnetically diluted samples can be prepared in analogy to Mg1–x Cox(H2O)2[B2P2O8(OH)2]•H2O (x = 0.25). The thermal stability of these compounds is very similar with a slight shift to higher decomposition temperatures for the Ni0.5Mg0.5(H2O)2[B2P2O8(OH)2]•H2O. In contrast to other borophosphates such as MIMII(H2O)2[BP2O8]∙H2O and MIII(H2O)2[BP2O8]∙H2O, it is not possible to rehydrate partially dehydrated samples even though the crystal structure may suggest this property. This shows that the aqua–ligands significantly contribute to the stability of the structure. The magnetic behavior of MII(H2O)2[B2P2O8(OH)2]•H2O (MII = Fe, Ni) corresponds well with separated 3d ions without strong magnetic interactions down to 1.8 K. Quite surprising was the remarkable change in the crystal habit that was observed during the synthesis upon addition of alkali–metal cations. Syntheses with the absence of alkali–metals lead to a change in the crystal habit by reducing of the number of faces in direction of the more simple prismatic morphology. Our research on borophosphates containing mixed transition metals led to the preparation of a borophosphate and a phosphate: FeCo(H2O)[BP3O9(OH)4], Fe1.3Co0.7[P2O7]∙2H2O The anionic partial structure of FeCo(H2O)[BP3O9(OH)4] is an open–branched tetramer built from (HO)BO3 sharing common O–corners with one (HO)PO3, one (HO)2PO2 and one PO4 group. The crystal structure is an isotype to Mg2(H2O)[BP3O9(OH)4]. Fe1.3Co0.7[P2O7]∙2H2O contains the diphosphate composed of two corner–sharing tetrahedra (isotypic to MII[X2O7]∙2H2O (MII = Mg, Mn, Co, Fe and X = P, As). However, the crystal structure of both, FeCo(H2O)[BP3O9(OH)4] and Fe1.3Co0.7[P2O7]∙2H2O, contains octahedral zigzag chains, which are interconnected by the respective tetrahedral anions. The octahedral chains in these crystal structures are closely related to the octahedral arrangements in MIIH2P2O7 (MII = Co, Ni) which exhibit a field-induced metamagnetic behavior from an antiferromagnetic state to a ferromagnetic state and to MII[BPO4(OH)2] (MII = Mn, Fe, Co) which indicate a low-dimensional antiferromagnetic correlation of the MII ions by dominant exchange interactions within the one–dimensional octahedral chain structure. Therefore, due to the similar structural features, FeCo(H2O)[BP3O9(OH)4] and Fe1.3Co0.7[P2O7]∙2H2O may exhibit interesting magnetic properties. Thermal investigation revealed that both compounds are stable until 300 ºC and transform into pyrophosphates at higher temperatures. Fe1.3Co0.7[P2O7]∙2H2O represents the first hydrated mixed divalent cation diphosphate.

With respect to the principles of biomineralization, it is of interest to study the crystallization of calcium oxalates under various experimental conditions. Calcium oxalates play decisive roles as biominerals in plants and as pathological “urinary/kidney stones” in vertebrates. Calcium oxalate exists in three different hydration states; calcium oxalate monohydrate (COM, monoclinic, a = 6.290(1)Å, b = 14.583(1)Å, c = 10.116(1)Å, β = 109.46°, P21/c), calcium oxalate dihydrate (COD, tetragonal, a = b = 12.371(3)Å, c = 7.357(2)Å, α = β = γ = 90°, I4/m) and calcium oxalate trihydrate (COT, triclinic, a = 6.11(1)Å, b = 7.167(2)Å, c = 8.457(2)Å, α = 76.5(2)°, β = 70.35(2)°, γ = 70.62(2)°, P ). Monoclinic COM and tetragonal COD are the most common phyto-crystals and the main constituents of kidney and urinary stones. The occurrence of calcium oxalates in plants represents a useful biogenesis (protection against herbivores) unlike the devastating occurrence in renal tubules. Therefore, biomineralization can be physiological or pathological. A systematic investigation of the morphological evolution of calcium oxalates in the presence of organic components is essential for understanding the mechanism of “pathological biomineralization”. In order to understand the pathological biomineralization of uroliths, it is necessary grow calcium oxalates comparable in morphology under similar growth conditions. The formation of calcium oxalate stones within a gelatinous state of proteins, polysaccharides, lipids and other biomacromolecules under a flow of supersaturated urine supports the fact that an “organic” gel model can simulate the process of urinary stone formation under in vitro conditions. Furthermore, synthetic polymers with precisely known functions and solution behaviours are better choices to understand the interaction of acidic proteins with calcium oxalates. Therefore, as a first step to unravel the complex pathology of uro/nephro lithiasis, we started to examine the structure and morphology of calcium oxalates crystallized in the presence of organic additives such as the sodium salt of polyacrylic acid (PAA) as well as agar gel. The influence of initial calcium oxalate concentration, pH and concentration of the additives on the formation of hydration states of calcium oxalates have been investigated along with the stated general methods. Apart from the three hydrated forms, calcium oxalate exists also in the anhydrous form (COA). Although three modifications of COA (α, β and γ) are reported in the literatures, the crystal structures and phase transformations were controversially discussed. We have been able to reveal the crystal structure of the β-modification of the anhydrous calcium oxalate by a combination of atomistic simulations and Rietveld refinements on the basis of powder X-ray diffraction pattern. β-COA belongs to the monoclinic system with unit cell parameters, a = 6.1644(3)Å, b = 7.3623(2)Å, c = 9.5371(5)Å, β = 90.24(2)°, P2/m (No. 10). The dehydration of COM was mimicked in silico to receive an initial model of the crystal structure of anhydrous calcium oxalate. This general approach may also be accessible for other decomposition processes ending up with crystalline powders of unknown crystal structure. No evidence for transformations from or to the α- or γ- modifications was found during our investigations. The growth pattern of COD crystals precipitated from aqueous solutions in the presence of PAA is clearly dependent on the concentration of PAA. By increasing the concentration of PAA, the shape of COD has been found to change from tetragonal bi-pyramids with dominant (101) pyramidal faces to tetragonal prisms with dominant (100) prism faces and finally to dumbbells. At still higher PAA concentrations, the morphology is reverted back to rod-like tetragonal prisms. Apart from these experiments, the interaction of PAA with (100) and (101) crystal faces of COD was explored with the aid of atomistic simulations. The simulation confirmed that during the development of the aggregates, strong interactions of PAA with the (100) faces take over control of morphologies. Our investigations show that the inner architecture of all the morphological varieties of COD was found to be dominated by an inner “core” consisting of thin elongated crystallites together with incorporated PAA and an outer “shell” formed as a consequence of secondary nucleation processes. We propose that for all types of COD aggregates, relative proportion of calcium oxalate and PAA dictates the shape and formation of nanometer sized crystallites which then aggregate and align to form the core. Such cores enriched with PAA may act as the sites for secondary nucleation events of calcium oxalate crystallites which then cover the core like a shell. In vitro experimental models for the growth of calcium oxalates can give valuable information on the growth and aggregation of urinary stones. Therefore, the “double diffusion technique” in agar gel matrix has been used for the biomimetic growth of calcium oxalate (COM) stones. A great variety of morphological forms of COM are produced in agar gel matrices (2 wt.-% agar gel of pH 8.5) ranging from platy crystallites to dumbbells and spherulites. The COM dumbbells and spherulites are assumed to be formed by the aggregation of smaller crystallites as a consequence of increased supersaturation inside the gel. Moreover, an increase of the pH value of the agar gel has been found to suppress the growth of COM and favours the growth of COD. The morphology of COD crystals grown in 2 wt.-% agar gel of pH 11.5 includes tetragonal prisms and dumbbells. The system calcium oxalate/ PAA/ H2O is a suitable model system for the investigation of principles of biomineral growth (shape development) in general. Our results demonstrate that the double diffusion technique in agar gel is a convenient route to grow calcium oxalate aggregates showing close resemblance to biogenic calculi and to study their ontogeny.

Reine und dotierte SnO2 Feinstpulver und Einkristalle wurden mit verschiedenen Methoden hergestellt. Die Abhängigkeit der Eigenschaften von der Dotierungsart und der Dotierungskonzentration wurde untersucht. Die Dotierung mit fünfwertigen Elementen (Sb, Nb) führt zur Erniedrigung des spezifischen elektrischen Widerstandes und die Dotierung mit dreiwertigen Elementen (z.B. In) zu seiner Erhöhung. An den dotierten Materialien kann mittels XPS eine Segregationsschicht nachgewiesen werden. Der Umfang dieser Schicht ist abhängig sowohl von dem Dotierungselement, als auch von den Herstellungsbedingungen (z.B. Temperatur und Temperungszeit). Für die Pulver wird, im Gegensatz zu den Einkristallen, kein thermodynamisches Gleichgewicht für Segregationsprozess im untersuchten Zeitfenster gefunden. In der vorliegenden Arbeit wird ein Model vorgestellt, dass es erlaubt, die Dicke der Segregationsschicht, als auch der verbleibenden Volumenkonzentration der Dotierungselement im SnO2 Kristallit zu berechnen. Die Volumenkonzentration beträgt in Abhängigkeit von der Dotierungsart und Temperatur bis zu 70% der gesamten Dotierungskonzentration. Die sich ausbildende Segregationsschicht erreicht einen Bedeckungsgrad von bis zu einer Monolage. Die Aktivierungsenergie der Diffusion, sowie die freie Enthalpie des Segregationsprozesses können für die hier untersuchten Dotierungselemente in SnO2 bestimmt werden.

Die Existenz metallreicher Perowskite der Zusammensetzung (SE3X)M (X = O, N; SE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Er, Ho, Tm, Lu; M = Al, Ga, In, Sn) wurde untersucht. Die Charakterisierung der Proben erfolgte mit Röntgenpulverdiffraktometrie und Elementaranalysen (O und N). Oxide (SE3O)Al mit SE = La, Ce, Pr, Nd und Sm und (SE3O)In mit SE = Ce, Pr und Nd wurden erhalten. Die Reihe der Verbindungen (SE3N)Al (SE = La, Ce, Pr, Nd, Sm) wurde um die Seltenerd-Metalle SE = Gd, Tb, Dy, Ho, Er und Tm erweitert. Die metallreichen Perowskite (SE3N)Sn (SE = La, Ce, Pr, Sm) und (SE3N)Ga (SE = Ce, Pr, Sm, Gd, Tb) wurden erstmals beschrieben. Die thermische Stabilität (DSC) der Phasen (SE3X)M ist für die Nitride allgemein am höchsten. Nitride von Al und Ga zersetzen zwischen 1000 °C und 1200 °C, Stannide bleiben bis 1250 °C thermisch stabil. Messungen der magnetischen Suszeptibilität und der LIII-Absorbtionskanten sind in Einklang mit einer Elektronenkonfiguration SE3+. Die gemessenen elektrischen Widerstände sind charakteristisch für schlechte metallische Leiter. Verschiedene Gehaltschnitte SE3Al-(SE3X)Al und SE3In-(SE3X)In wurden mit Röntgenpulverdiffraktometrie und DTA untersucht. Die Oxide und Nitride (SE3X1-y)M (SE = La, Ce; X = N, O) weisen nur geringe Phasenbreiten auf. Die Carbide (Ce3C1-y)In zeigen hingegen signifikante Phasenbreiten. In den Systemen EA-In-N wurden röntgenografisch phasenreine Pulver von (Ca4N)[In]2 und (EA19N7)[In4]2 (EA = Ca, Sr) erhalten. Durch Elementaranalysen auf H, C, N, O, EA und In und Neutronenbeugung am Pulver können alternative Zusammensetzungen mit einer ausgeglichenen Ladungsbilanz im Sinne des Zintl-Konzepts für diese Phasen ausgeschlossen werden. Im System La-Al wurde die neue Phase La16Al13 beobachtet und an Einkristallen sowie an Pulvern charakterisiert. Das in der Literatur im Cu3Au-Strukturtyp beschrieben kubische Polymorph von Ce3Al wurde auf einen ternären metallreichen Perowskit (Ce3X)Al zurückgeführt.

The main focus of the present work was the Ge-rich part of the binary Ba – Ge system, in which by inspecting the behavior of the clathrate-I Ba8Ge43 under pressure, several new phases were found. The new phases in this system have the following compositions: BaGe3 (with two modifications), BaGe5, BaGe5.5 and BaGe6, therefore they are quite close in composition range: 75% - ~85% at. Ge. Concerning the conditions required for the synthesis of each phase, several combinations of temperature and pressure were employed in order to find a stability range. It was possible to establish such a formation range for all phases. In some cases two phases were found for a given conditions and in many other cases three or more phases were found to coexist. Thus, the stability range of pressure and temperature for single phase formation turned out to be very narrow. By inspecting of some structural features, for instance the interatomic distances, it is found that the average of the Ge – Ge distances change in line with the composition, i.e. the shorter contacts belong to BaGe6 while the longer distances are present in BaGe3 (both modification). An opposite trend is observed for the calculated density of each phase (neglecting the tI32 form of BaGe3): the lower density is found for BaGe3 and the denser compound is found to be BaGe6. Of course this is not coincidence, since due to the Ge content, BaGe6 has the largest molar mass. Similarly, by examining the density as a function of the interatomic distance. In such case, the denser compound is characterized by shorter Ge – Ge contacts, while the less dense phase holds the longest Ge – Ge contacts. This is in agreement with the building motifs within each crystal structure: columns in BaGe3 (open framework) passing through layers in BaGe5, ending in a three-dimensional network (closed framework) in BaGe6.

Die ternären Systeme Ti/P/Te, Ce/P/Te und Si/P/Te wurden in der vorliegenden Dissertation hinsichtlich der Existenz neuer Verbindungen untersucht. Diese Verbindungen wurden insbesondere in Bezug auf ihre thermochemischen Eigenschaften charakterisiert. Durch Kombination von experimentellen Untersuchungen und thermodynamischen Modellierungen der ablaufenden Festkörper-Gasphasen-Gleichgewichte konnten die Synthesen der neuen Verbindungen optimiert werden. Abschließend erfolgte zudem die physikalische und kristallographische Charakterisierung der gefundenen Phosphidtelluride.