Palladium-based Ferroelectrics

该学生将制作和表征钛酸铅锆酸盐（PZT）和钛酸铅样品，在钙钛矿b位点上取代30%的钯，取代钛。生长将以陶瓷粉末的形式，压成颗粒，电极溅射。表征将强调介电测量（介电常数和损耗）作为温度的函数，从低温水平（约20K）到升高水平（约500C），它还将包括磁测量，电子显微镜，x射线研究，可能还有比热测量。将根据现有的多铁性、磁电晶体模型进行分析，包括Blinc等人的模型。由于Pd通常是非磁性的，但已知在外加电场和/或单轴机械应力下会变成磁性，因此也将使用Tula Paudel和Evgeny Tsymbal的2016年模型。它们的密度泛函计算表明，为了同时发生磁性和铁电性，一些Pd必须处于+4价态，一些Pd必须处于+2价态，而且它们不可能全部进入Ti+4位；相反，一些必须在超大的Pb+2位置偏离中心。虽然钯很昂贵，但预期的设备是薄膜存储器，而且钯的数量非常小，每个芯片的额外成本只有几便士。由于PZT是领先的室温铁电器件材料（例如，用于汽车燃油喷射器），这表明了大批量实际商业产品的潜力。

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.