PROPERTIES OF STRUCTURALLY AND CHEMICALLY COMPLEX MATERIALS
Negative thermal expansion
ZrW2O8 has been show to exhibit negative
thermal expansion over a wide temperature range.
Materials with the Sc2(WO4)3 structure
have also been shown to display negative thermal expansion over a wide
temperature range. Sc2(WO4)3 itself shows a bulk volume
contraction from 10 K to at least
800 K. A wide range of A and M cations can be substituted into
this
structure type, leading to materials with controllable expansion
properties.
More information at http://www.dur.ac.uk/john.evans/webpages/nteintro.html
Thermoelectric materials http://www.its.caltech.edu/~jsnyder/Research.html
The thermoelectric effect is the coupling between a temperature
gradient and electric field.
Thermoelectric materials convert heat flow into electrical current -
and vice versa. For example, thermoelectric elements in NASA
spacecraft visiting the outer planets convert heat energy into
electrical energy to power the spacecraft (when
solar power is not feasible). Similarly,
thermoelements in a battery powered picnic cooler use electric current
to pump heat from the inside of the cooler to the outside, or be used
to cool microprocessors on computer chips. Thermoelectric sensors are
widely used for the measurement of thermal quantities.
Some new materials that have been investigated include skutterudites
(below),
Chevrel
phases
(Cuw,
CuxFey, or Tiz)Mo6Se8
[where w<4, x<2, y<1, and z<1]
, and
solid solutions of beta-Zn4Sb3
and
Cd4Sb3.
YbFe4Sb12 (skutterdite)
from http://wyvern.phys.s.u-tokyo.ac.jp/~fujimori/Research/arch/thermo.pdf
More information about the search for new materials
http://www.zts.com/darpa/dubois99/ppframe.htm
http://www.its.caltech.edu/~jsnyder/Research.html
Correlated-electron physics in transition-metal oxides:
spin/charge/orbital ordering
See article in Physics Today, July 2003
- metal-insulator transition, stripe phases
- colossal magnetoresistance (CMR): perovskite-structure prototype
(La,Ca)MnO3
http://www.ill.fr/dif/3D-crystals/magnets.html
- high-Tc superconductivity: La2-xSrCuO4 (Tc=40K),
YBaCu3O7 (Tc=93K), and a more complex
Hg-cuprate
superconductor (Tc>150K).
http://www.ill.fr/dif/3D-crystals/superconductors.html
- magnetic oxide semiconductors
from R. Vidya et al., Phys. Rev. B65, 144422 (2002)
Ferroelectrics and active materials http://www.mri.psu.edu/faculty/gopalan/Materials.htm
Loosely
speaking, ferroelectrics are electrical analogues to ferromagnets. Ferroelectrics
have frozen-in electrical dipoles in their crystal structure in the
absence of any external fields. These
dipoles can be
switched to various orientations (determined by crystal symmetry) using
external
fields. Regions of uniform dipoles are
called
domains, and two different ferroelectric domains differ in their
dipole
orientations, and are separated by a domain wall.
Ferroelectrics
bundle
a number of electrical, elastic and optical properties in one material,
leading
to many cross-coupled phenomena such as piezoelectricity (electric
fields
and elastic strains), pyroelectricity
(temperature
gradients and electric fields), electro-optic (refractive index to
electric
fields), elasto-optic (strains to index), photorefraction (light
induced
electric fields and optical changes), and nonlinear optical properties
(such
as optical frequency conversion).
LiNbO3 (not in the
perovskite
structure):