Palladium-based Ferroelectrics

The student will fabricate and characterize samples of lead-zirconate titanate (PZT) and lead titanate with up to 30% palladium substituted at the perovskite B-site, replacing titanium. Growth will be in the form of ceramic powders, pressed into pellets, with electrodes sputtered on. Characterization will emphasize dielectric measurements (permittitivity and loss) as functions of temperature from cryogenic levels ca. T=20K to elevated levels (>500C), and it will also include magnetic measurements, electron microscopy, X-ray studies, and probably specific heat measurements.

Analysis will be in terms of existing models for multiferroic, magnetoelectric crystals, including the model of Blinc et al. Since Pd is normally not magnetic but is known to become magnetic under applied electric fields and/or uniaxial mechanical stress, the 2016 model of Tula Paudel and Evgeny Tsymbal will also be used. Their density functional calculations imply that for simultaneous magnetism and ferroelectricity to occur, some of the Pd must be in +4 valence state and some in +2, and moreover, that it cannot all go into the Ti+4 site; instead some must go off-center in the oversized Pb+2 site.

Although Pd is expensive, the intended devices are thin-film memories, and the Pd amounts are so small that the added cost would be only a few pence per chip. Since PZT is the leading room-temperature ferroelectric device material (e.g., for automobile fuel injectors), this suggests the potential for large-volume real commercial products.