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 Srn+1TinO3n+1 Ruddlesden-Popper (RP) phases under tensile biaxial strain, where beyond a critical layer thickness n>nc, 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.
