The search for materials with desired magnetic and electrical properties concomitantly relies on the discovery of new systems. To unequivocally determine the compounds&’ innate properties, large single crystals must be grown and characterized. In this talk, I will focus on the versatility and tunability of properties of intermetallics as it applies to the design and discovery of compounds with unusual magnetic and electrical properties. The challenges of phase stability, single crystal growth, structure determination, and physics of these materials will also be discussed.

Alkaline earth metals such as calcium and magnesium are low-melting and reactive toward many elements in the periodic table; this makes them useful as solvents for metal flux reactions. Their melting points can be lowered further by mixing them with other elements; a 50/50 Ca/Li mixture melts at 300 C, and eutectic mixtures of Mg/Al and Ca/Mg both melt at ca. 450 C. Reactions of iron with rare earths and silicon in Mg/Al fluxes produce complex multinary phases including R₅Mg₅Fe₄Al₁₂Si₆, R₃FeAl_4-xMg_xSi₂, and RFe₂Al_7-xMg_x (R = rare earth). All of these structures feature a similar building block of chains of face-sharing aluminum trigonal prisms which are centered by iron. Pseudo-Zintl phases such as CaMgSi and EuMgSn can also be grown in this flux; these compounds are close to a metal-insulator transition and exhibit interesting properties such as magnetoresistance. Calcium-rich fluxes are excellent solvents for carbon and CaH₂, enabling the formation of complex metal carbides and hydrides. These products range from charge-balanced salt-like Ca₁₁Sn₃C₈ and LiCa₂C₃H to phases incorporating a range of hydride and/or carbide interstitials, such as Ca₄₈In₁₃C_4-xH_23+x.

Topochemical reactions can be utilized to direct structure and properties in various compounds. Recent efforts in our group have involved the insertion of cation and/or anion species into layered perovskites via oxidative/reductive intercalation and/or ion exchange. In one case, we have found that the use of reductive intercalation with alkali metals, followed by oxidative intercalation with chalcogen hydride gases, allows for the construction of alkali-metal chalcogen hydride layers within Dion-Jacobson-type hosts; layered perovskites like RbLaNb2O7 can be manipulated to introduce Rb-ChH layers (ChH = OH, SH) within the interlayer. In other systems, two-for-one ion exchange reactions can be carried out on Ruddlesden-Popper perovskites; reactions of K2SrTa2O7 with divalent transition metal ions result in compounds of the form, MSrTa2O7 (M = Co, Zn). Details on the synthesis and characterization of these products will be presented with a discussion on the utility of these set of reactions for manipulations of other solids.

Development of new routes to magnetic materials is a crucial step for the next generation of energy solutions. Besides the energy savings upon synthesis, low temperature methods significantly enhance the capabilities of fine tuning of the structure and properties of a magnetic material. A recent example is an intercalation of Li-ammonia or Li-pyridine into interlayer space of FeSe superconductor, which leads to the significant increase of the superconducting transition temperature. Products of the Li-amines intercalation into pre-synthesized FeSe are fine powders with low degree of crystallinity. Temperatures of conventional solid state synthesis of FeSe (> 1000 K) are not compatible with organic amines. We have developed low temperature (T < 500 K) synthetic route to iron chalcogenides, FeQ (Q = S, Se, Te). The developed method allows us to modify crystal structure of layered FeQ chalcogenides by means of the intercalation of iron-amino complexes. Unlike traditional intercalation techniques, high quality single crystals were obtained, thus facilitating determination of the crystal structure and evaluation of the properties of the synthesized compounds. Synthesis of new materials, their crystal and electronic structure as well as magnetic properties will be discussed.

Our ability to design new materials with desired electrochemical, thermoelectric or strongly-correlated electron properties is limited by thermodynamic control over reaction products in traditional high-temperature synthetic procedures. On the contrary, topotactic reactions, where extensive parts of the original framework are retained, allow for greater control of the structure of the final products; therefore, a combination of desired structural features, spin and oxidation states can be produced in a final material in a predictable fashion.
A 'chimie douce' solvothermal reduction method was developed for topotactic oxygen deintercalation of complex metal oxides. The reduction of the Ruddlesden-Popper nickelate La₄Ni₃O₁₀ was used as a test case to prove the validity of the method. The completely reduced phase La₄Ni₃O₈ was produced via the solvothermal technique at 150°C - a lower temperature than by other more conventional solid state oxygen deintercalation methods. Unlike other techniques, a pure Ni¹⁺ compound, LaNiO₂, can be prepared by solvothermal reduction, demonstrating the advantages of the developed method for synthesis of highly metastable reduced compounds.
Metastable oxyfluorides SrFeO₂F and La₄Ni₃O₈F₂ were prepared through a low temperature, multistep synthesis via fluorination of the infinite layer intermediate phases. Influence of the synthetic pathway on O/F short range ordering and physical properties will be discussed. Mossbauer spectroscopy measurements revealed the predominance of cis fluorine configuration in FeO₄F₂ polyhedra, confirming a difference in local Fe coordination in comparison with O/F disordered SrFeO₂F.
When trying to achieve anion ordering during synthesis, it is important to perform anion intercalation at as low a temperature as possible to avoid thermal randomization of the anions. A low temperature solvothermal fluorination technique, which we developed, allows for fast and facile synthesis at lower temperatures than gas- solid fluorination by XeF₂.
In all known compounds with the alpha-NaFeO₂ structure transition metals oxidation states are either 3+ or 3+/4+. We have developed an “aliovalent exchange plus intercalation” multistep soft chemistry approach for the preparation of a series of new layered transition metal oxides. The synthetic procedure resulted in compounds with the alpha-NaFeO₂ type structures and, uniquely, with transition metals in mixed valent 2+/3+ oxidation states. The oxidation state in the final compounds can be controlled by utilizing A_xMO₂ precursor phase with different x. Crystal structures and physical properties of these novel compounds will be presented.

The structures of the metal-cyanide layers within the group 10 compounds Ni(CN)2, Pd(CN)2 and Pt(CN)2, which consist of vertex-sharing square-planar M(CN)4 units, have recently been determined in detail using total neutron diffraction and will be discussed. Moving to group 11, the binary cyanide, Cu(CN)2, is not known to exist. However, we show here that copper(II) can be stabilised in a cyanide-only environment in the stoichiometric, mixed copper-nickel cyanide, CuNi(CN)4, and in the solid-solution, Cu1-xNi1+x(CN)4 (½ le; x < 1).
The atomic structure of the layers in CuNi(CN)4 and the stacking relationship between nearest-neighbour layers have been determined from total neutron diffraction studies at 10 and 300 K. The structure consists of flat layers of perfectly square-planar [Ni(CN)4] and [Cu(NC)4] units linked by shared cyanide groups i.e. both the metal and cyanide groups are perfectly ordered with Cu(II) coordinated to the nitrogen end of the cyanide group and Ni(II) to the carbon end. It is rather unusual to find Cu(II) in a square-planar environment within an extended solid. The layered structure of this new mixed-metal cyanide is closely related to those of Ni(CN)2, which forms more extended sheets, and Pd(CN)2.xNH3 and Pt(CN)2.xH2O, which form as nanocrystalline materials.
The overall appearance of the powder X-ray diffraction pattern of CuNi(CN)4, including the unusual peak shapes of the observed Bragg reflections, has been successfully explained using models incorporating stacking disorder between next nearest neighbour layers. CuNi(CN)4 shows similar thermal expansion behaviour to that observed previously for Ni(CN)2 [1,4] with negative thermal expansion within the layers (αa = -9.7 MK-1) and positive thermal expansion between the layers (αc = +89 MK-1) measured over the temperature range 200-540 K.
The stability of Cu(II) atoms in a cyanide-only environment has been investigated by varying the ratio of the Cu2+ and Ni2+ ions used in the synthesis. Using a Cu:Ni ratio of 1:1, the anhydrous phase, CuNi(CN)4, is precipitated directly. For Cu:Ni ratios less than one, hydrates of the form Cu1-xNi1+x(CN)4.yH2O (½ le; x < 1; y le; 6) are produced which can be dehydrated to form the corresponding anhydrous compounds, Cu1-xNi1+x(CN)4. These compounds readily rehydrate. Replacement of Cu2+ by Ni2+, which occurs when the Cu:Ni ratio is less than one, leads to the creation of [Ni(NC)4] units. These in turn readily hydrate to form six-coordinated [Ni(NC)4(H2O)2] groups similar to those found in nickel-cyanide hydrates, such as Ni(CN)2.3H2O. [Ni(CN)4] units do not hydrate; hence CuNi(CN)4, which contains such units, is not found in a hydrated form. With Cu:Ni ratios above one, partial reduction of the Cu(II) occurs to form LT-CuCN, in addition to CuNi(CN)4. This result further confirms that Cu(II) ions can only be stabilised when connected to the nitrogen ends of bridging cyanide

The discovery of giant magnetocaloric effect (MCE) in rare-earth and transition metal based materials and prototype equipment development has sparked great interest for magnetic cooling technology. This has also made it a promising alternative to the current vapor compression technology. However, significant synthetic challenges for industrial scale production of MCE materials exist for the successful commercialization of this technology.
We have focused our research activities on the Mn_xFe_2minus;xP_ySi_1-y family of magnetocaloric materials which shows great promise due to their large magnetocaloric properties as a result of being first-order phase transition materials (Tegus et al. 2002, Thanh et al. 2008). Additionally, they exhibit tunable Curie temperatures and earth abundant constituent raw materials. Moreover, they possess excellent long-term stability and their ability to be formed into complex shapes. In this presentation, we will discuss some of the challenges encountered during the up-scaled production of these materials, and how these have been overcome using industrial synthetic routes (for e.g. meltspinning and atomization) in addition to more traditional academic ball milling approach. We will also discuss the magnetocaloric properties of the obtained materials and the performance of these materials during magnetocaloric cycling.
REFERENCES
Tegus, O.; Brück, E.; Buschow, K.; de Boer, F., Transition-metal-based magnetic refrigerants for room-temperature applications, Nature2002, 415, 150.
Thanh, D.; Brück, E.; Trung, N.; Klaasse, J.; Buschow, K.; Ou, Z.; Tegus, O.; Caron, L., Structure, magnetism and magnetocaloric properties of MnFeP1-xSix compounds, J. Appl. Phys.2008, 103, 07B318.

Accommodation of excess oxygen in CeO₂, ThO₂ and UO₂ has been investigated using ab-initio modelling. Hyperstoichiometry was preferentially accommodated by the formation of peroxide species in CeO₂, ThO₂ but not in UO₂, where oxygen interstitial defects are dominant. Migration of the excess oxygen defects was also studied; the peroxide ion in CeO₂ and ThO₂ is transported via a different mechanism to the oxygen interstitial in UO₂. Formation of Frenkel defects was investigated to understand the eect of a peroxide formation on the drive for defect recombination. The presence of the Frenkel vacancy in proximity to the associated additional oxygen defect induces the oxygen to take up an interstitial site, similar to excess oxygen defects in UO₂ rather than remain part of a peroxide molecule.

Mn-doped CeO2 electrolytes were prepared using a soft chemical technique which involved co-precipitation of Mn2+ and Ce4+ using oxalic acid as the precipitant. The incorporation of MnO into ceria lattice was found to be pH dependant. A wider solubility range of managanese dopant concentration into ceria lattice prepared via this method is highlighted. The resultant powders of Mn-doped CeO2 solid solutions, formulated as Ce1-xMnxO2-x, (0.05 le; x le; 0.25), were investigated thoroughly for the first time, from the aspect of synthesis where pH was precisely controlled and varied from 5 - 11. The optimized pH for a stable incorporation of Mn dopant into ceria was found to be pH = 10, in order to obtain the correct stoichiometric compound. The solubility limit of MnO in the CeO2 fluorite lattice structure was suggested to be x = 0.20. The phase composition, morphology properties and elemental analysis of the oxalate and derived-powder was characterized using X-ray diffraction, DTA/TG, SEM and X-ray fluorescence (XRF) respectively. The grain size decreases with increase of MnO content. The electrical conductivity of sintered samples of Mn-doped CeO2 ceramics were investigated in air as a function at 473 - 1073 K using AC impedance spectroscopy. The contributions of the bulk (grain interior), the grain boundary and the electrode polarization behaviour are well documented. The bulk conductivities of the Mn-doped CeO2 ceramics sintered at 1473 K at a test temperature of 1073 K were determined to be 4.223 x 10-4 S cm-1 for Mn content x = 0.10 with activation energy, Ea = 0.88 eV.

Magnetic ceramic nanoparticles of the type xIn2O3-(1-x)alpha-Fe2O3, xV2O5-(1-x)alpha-Fe2O3 and xZnO-(1-x)alpha-Fe2O3 (x=0.1-0.7) were synthesized from the mixed oxides using mechanochemical activation for 0-12 hours. X-ray diffraction was used to derive the phase content, lattice constants and particle size information as function of ball milling time. Mossbauer spectroscopy results correlated with In3+, V5+ and Zn2+ substitution of Fe3+ in the hematite lattice. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced systems with a wide range of particle size distribution, from nanometer particles to micrometer agglomerates, but with a uniform distribution of the elements. Simultaneous DSC-TGA investigations up to 800 degrees C provided information on the heat flow, weight loss and the enthalpy of transformation in the systems under investigation. This study demonstrates the formation of a nanostructured solid solution for the indium oxide, an iron vanadate (FeVO4) for the vanadium oxide, and of the zinc ferrite (ZnFe2O4) for the zinc oxide. The transformation pathway for each case can be related to the oxidation state of the metallic specie of the oxide used in connection with hematite.
NSF-DMR-0854794

Metal-Organic Frameworks (MOFs) have gained a tremendous amount of attention in the past few decades. Due to the tunable nature of their ligand geometry, their enormous surface area and their large gas uptake capacities, MOFs are widely applied in many areas such as gas storage, gas separation, CO2 capture, catalysis, drug delivery, sensors, photosensitive materials and magnetic materials. However; it is still problematic to construct MOFs with large porosity, high stability and good crystal quality, while many potential MOF applications require them to possess those properties simultaneously. Typically, in order to attain larger pore sizes and surface areas, researchers attempt elongation of MOF constructional units. However, this will often inherently undermine the framework stability and crystallinity and increase the possibility of framework interpenetration. Additionally, recent research indicates that the crystal size, quality and morphology can largely affect the surface area of the resulting MOFs.
The MOFs based on the ultrastable zirconium polyoxo clusters have demonstrated their excellent stability toward air, water, or even concentrated acid. Even though a limited number of Zr MOFs were published, many of them suffer from a low crystallinity and limited pore sizes. In this work, a series of non-interpenetrated zirconium MOFs were synthesized from a group of tetrahedral ligands via a modulated synthesis strategy. All of them possess new MOF topologies, large cavities and high crystal quality. Two categories of polymorphic MOFs can be identified and their isostructural MOFs were obtained by using elongated analogous ligands. Remarkably, PCN-525 has largest surface area, pore size (up to 25Å) and solvent accessible volume (up to 84.10%) among all the MOFs constructed from tetrahedral ligands. It is one of the rare examples of mesoporous Zr MOFs with three dimensional channels. PCN-522 is the first MOF that contains two distinctive Zr-based clusters, which has an unprecedented 4, 12, 12-connected topology that incorporates tetrahedra, cuboctahedra and icosahedra in the same network. This work provides both insights into novel framework topologies with tetrahedral building units and a practical method of constructing MOFs with large pore size and high stability.