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Layered Ferroics as Superior Microwave Dielectrics

The Penn State MRSEC IRG1 tean
(Strain-enabled multiferroics), in close collaboration with the Cornell MRSEC,
U Maryland, NIST and others, has designed and demonstrated the world
s best tunable microwave dielectric
to date operating with the highest reported figure of merit up to 125 GHz.
This could result in a new
generation of superior electronically tunable microwave filters, antennas, and
phase shifters for improved wireless communications using cellular telephones
and other devices.  The team
predicted an unusual polar state in Sr
n+1TinO3n+1 Ruddlesden-Popper (RP) phases under tensile
biaxial strain, where beyond a critical layer thickness
an in-plane polarization sets in within the perovskite layers.  This indicates the importance of the dimensionality
 n in turning on and off the
ferroelectric properties. Moreover, these layered structures are believed to
accommodate nonstoichiometry through the formation of additional rock-salt
layers (SrO), thus significantly decreasing dielectric losses.