Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Abstract: C1.00202 : Negative thermal expansion in Prussian Blue analogs
Author:
While many Prussian Blue (PB) analogs are known to display
negative thermal
expansion (NTE), few have been studied in detail. Not all
compounds in this
family exhibit NTE. Because it is possible to systematically vary
ion size
and charge in these materials, they represent an interesting
playground to
study NTE and possible correlations with electronic and crystal
structures.
By contrast with many silicates displaying NTE and in which
tetrahedral
units are linked with apical oxygens, the octahedral units in PB
compounds
are linked with a linear cyanide ligand. This introduces more
degrees of
freedom in the (mostly) cubic PB structures compared to the
silicates.
Polycrystalline samples of PB analogs,
$M^{II}_{2}$\textit{[Fe}$^{II}$\textit{(CN)}$_{6}]$ and
$M^{III}_{2}[A^{III}$\textit{(CN)}$_{6}]_{2}$\textit{(M = Mn, Co,
Ni, Cu, Zn; A = Cr, Fe, Co) }were synthesized via standard chemical
precipitation. Variable temperature X-ray powder diffraction
patterns were
collected \textit{in-situ} in the range 300-123 K to study the
T-dependence of the lattice
parameter and to obtain an average coefficient of thermal
expansion (CTE).
Lattice parameters were extracted using the Rietveld refinement
technique
with the General Structure Analysis System (GSAS) software. The
determined
average CTEs, for the compounds showing NTE behavior, are in the
range -4.9
x 10$^{-6 }$K$^{-1}$ to -39.5 x 10$^{-6}$ K$^{-1}$ while the CTEs
for the
other materials showing positive TE behavior are in the range 5.9
x 10$^{-6
}$K$^{-1}$ -- 59.2 x 10$^{-6}$ K$^{-1}$.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.C1.202
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