Characterization of Thin Film CuCr2Se4 Synthesized by A Modulated Elemental Reactant Deposition

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Turbostratic Disorder in [(Bi2Te3)x(TiTe2)y] Superlattices

ABSTRACTA family of metastable [(Bi2Te3)x(TiTe2)y] superlattices (where × and y denote the number of layers of each of the two components) was prepared by annealing modulated elemental reactant precursors at temperatures below 280°C. Structural analysis by traditional XRD shows the superlattice structures are highly aligned to the substrate with many orders of diffraction peaks from the c direction of the superlattice. Off-axis diffraction techniques presented in this paper suggest that the order between the layers in the a-b direction of these superlattice structures is turbostratic. In this type of behavior, the quasi two-dimensional crystals of Bi2Te3 and TiTe2 that comprise the superlattice structure lie like a deck of cards thrown in disarray on a surface. An analysis of the diffraction data leading to this conclusion is given.

Rational Synthesis of The Metastable Compounds BixCo4-xFexSb12

The synthesis of many targeted ternary compounds using conventional synthesis approaches has been unsuccessful because the ternary compounds are thermodynamically unstable with respect to disproportionation to a mixture of binary compounds. Typically these compounds have been synthetic targets based on predictions of enhanced properties. The ternary skutterudites with formula M'xM4Sbl2 (where M' = La, Lu, Y) are prime examples. Compounds with this structure have been found to be very promising thermoelectric materials having both good electrical properties and low thermal conductivities. Inserting heavy M' atoms into this crystal structure has been predicted to further decrease the thermal conductivity by increased phonon scattering. Attempts to make the title compound using conventional synthesis approaches failed due the formation of binary compounds as reaction products. Using modulated elemental reactants we were able to prepare the title compound at 160°C. Annealing at temperatures above 500°C resulted in exothermic decomposition into binary compounds. The Bi containing compounds are therefore thermodynamically unstable with respect to disproportionation at all temperatures. The amount of Bi can be varied by varying the composition of the starting modulated elemental reactant. Preliminary measurements to determine the variation of electrical conductivity and Seebeck coefficient as a function of bismuth content are presented.