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The past year of funding has been very productive.  Through the work done on the PRF grant, we were awarded an NSF-MRI grant (NSF-MRI-0922931) to purchase a single crystal X-ray diffractometer.  In addition, funding from PRF and TCNJ were used to purchase a powder X-ray diffractometer at the same time.  The Bruker Apex 2 and Bruker Focus D8 instruments were installed in December 2009 and March 2010.  The two instruments dramatically increased our productivity and have excited students working on X-ray characterization based projects.

            We have spent considerable time working on several projects that were stalled because of the lack of X-ray diffraction facilities.  We have completed the studies of Cs₆Nb₄Se₂₂ and K₁₂Nb₆Se_35.3 and published the results in Acta Crystallographica C:  Communications.  The structures are closely related to each other through the formation of niobium selenide polyhedra.  The structural diversity and relationships to literature structures were discussed in the paper.

            Our original proposed project has proven to be difficult.  We found a large thermodynamic sink in the formation of black Se crystals when LaCl₃ is reacted with K₂P₂Se₆ in acetonitrile at 150 C for three days.  Even with shorter reaction times, the formation Se was favored.  We attempted some exploratory work by reacting LaCl₃ with Ge, K₂S₂, and additional S in water, methanol, ethylene diamine, and acetonitrile under solvothermal conditions.  We obtained clear crystals after reacting for only 2 days in ethylene, however the materials were oxides instead of sulfides.  The crystal structure could not be finished.  Further EDS studied confirmed the formation of oxides.  We were disappointed and may return to this project at a later time.

            We have been much more successful in the use of alkali chalcogenide fluxes (A₂Q_n; A=K, Cs; Q=S, Se) to react a variety of metals.  We have discovered a new superconducting phase based on K_xNbSe₂, but have had difficulty in reproducing the structure and superconducting phase.  We do understand PRF does not fund these types of compounds, however, we believe we have discovered a new avenue of research.  Several students are trying to reproduce the superconductor and also explore selenium analogs of the novel arsenide superconductors.  If the compounds can be made, we anticipate submitting a grant to NSF to fund this side of the project.

            Our current most active project has led us to energy related materials.  We have begun to explore quaternary phase space to discover new potential thermoelectric materials.  We used the Cs-Bi-Te thermoelectric materials discovered by Kanatzidis as our model system and began to logically modify the structures.  The Cs in the structure disrupted the NaCl-type structure of the Bi-Te, which decreases the translation of phonons and the conduction of heat through the material.  We hypothesized that the addition of another element, a rare earth, with its higher coordination environment may further disrupt the structure.  We began to explore the K-La-Bi-Se composition space for novel compounds.  We discovered a new compound K₂La₂Bi₂Se₉ with a novel structure.  The La and Bi polyhedra alternate to form wave-like slabs.  The gaps in the waves form channels where the K resides.  The oxidation state of Bi was determined to be 3+ through the stoichiometry and we recently obtained XPS data, which indicates the Bi is in a mixed oxidation state +3 and +5.  We are doing further studies through bond valence calculations and magnetic studies to confirm the mixed oxidation states.  The structure is also being reexamined for supercells. Very preliminary resistivity experiments showed the compound was not conductive so further thermoelectric properties were not explored in this compound.  We are now preparing a communication to be sent to Inorganic Chemistry to disseminate our results.  We are now working on preparing a series of rare earth analogs of the structure and anticipate a publication for Journal of Solid State Chemistry by the end of the funding period. If we discover a compound has a strong thermoelectric effect, we will publish the full paper in Materials Chemistry.

Impacts of the PRF Grant

            We have had a very exciting year and the PRF grant allowed us to purchase a Powder XRD in addition to the single crystal XRD.

            The project has funded two student projects directly Sarah Wehrhan (2011, applying to graduate schools) over an 8 week summer session and Rachel Roesch (2012) during the academic year.  Rachel Roesch and Matthew Kita have committed to working on the PRF grant during the summer of 2011.

            The PRF grant has led to one publication in Acta Cryst. C and one in preparation for Inorganic chemistry.  A full paper is expected towards the end of the grant period.  In addition, several other crystal structures have been collected and could be published in Acta Cryst E; however, we are focusing our efforts on higher impact work.