94 research outputs found
High-Temperature Transport Properties of Yb4−xSmxSb3
Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K
X-ray Absorption Studies of Ceria with Trivalent Dopants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65899/1/j.1151-2916.1991.tb04328.x.pd
Effect of Ta 2 O 5 , Nb 2 O 5 , and HfO 2 Alloying on the Transformability of Y 2 O 3 -Stabilized Tetragonal ZrO 2
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65528/1/j.1151-2916.1990.tb05100.x.pd
Ab Initio Study of the Structural Phase Transition in Cubic Pb_3GeTe_4
In the substitutionally disordered narrow-gap semiconductor Pb_{1-x}Ge_xTe, a
finite-temperature cubic-rhombohedral transition appears above a critical
concentration . As a first step towards a first-principles
investigation of this transition in the disordered system, a (hypothetical)
ordered cubic Pb_3GeTe_4 supercell is studied. First principles
density-functional calculations of total energies and linear response functions
are performed using the conjugate-gradients method with ab initio
pseudopotentials and a plane-wave basis set. Unstable modes in Pb_3GeTe_4 are
found, dominated by off-centering of the Ge ions coupled with displacements of
their neighboring Te ions. A model Hamiltonian for this system is constructed
using the lattice Wannier function formalism. The parameters for this
Hamiltonian are determined from first principles. The equilibrium
thermodynamics of the model system is studied via Metropolis Monte Carlo
simulations. The calculated transition temperature, T_c, is approximately 620K
for the cubic Pb_3GeTe_4 model, compared to the experimental value of T_c
\approx 350K for disordered Pb_{0.75}Ge_{0.25}Te. Generalization of this
analysis to the disordered Pb_{1-x}Ge_xTe system is discussed.Comment: 38 pages, LaTeX, 11 PostScript figure
Symbiotic relationship between brain structure and dynamics
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