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The room temperature electronic transport properties of 1 μm thick Bi0.4Sb1.6Te3 (BST) films correlate with overall microstructural quality. Films with homogeneous composition are deposited onto fused silica substrates, capped with SiN to prevent both oxidation and Te loss, and postannealed to temperatures ranging from 200 to 450 °C. BST grain sizes and (00l) orientations improve dramatically with annealing to 375 °C, with smaller increases to 450 °C. Tiny few-nanometer-sized voids in the as-deposited film grain boundaries coalesce into larger void sizes up to 300 nm with annealing to 350 °C; the smallest voids continue coalescing with annealing to 450 °C. These voids are decorated with few-nanometer-sized Sb clusters that increase in number with increasing annealing temperatures, reducing the Sb content of the remaining BST film matrix. Resistivity decreases linearly with increasing temperature over the entire range studied, consistent with improving crystalline quality. The Seebeck coefficient also improves with crystalline quality to 350 °C, above which void coalescence and reduced Sb content from the BST matrix correlate with a decrease in the Seebeck coefficient. Nevertheless, a plateau exists for an optimal power factor between 350 and 450 °C, implying thermal stability to higher temperatures than previously reported. [ABSTRACT FROM AUTHOR]

In this paper we show that experimentally realizable apparently piezoelectric thin-film superlattices can be created from nonpiezoelectric materials provided an odd-order (e.g., trilayer) stacking sequence is used. The size-dependent mechanism of flexoelectricity, which couples gradients of strain to polarization, allows such a possibility. We present closed-form analytical expressions for the response of various thin-film and superlattice configurations. We also clarify some of the subtleties that arise in considering interface boundary conditions in the theory of flexoelectricity as well as the relationship of flexoelectricity to the frequently used polarization gradient terms used in modeling ferroelectrics. We find that for certain (optimum) material combinations and length scales, thin-film superlattices yielding apparent piezoelectricity close to 75% of ferroelectric barium titanate may be achievable. [ABSTRACT FROM AUTHOR]

Amorphous Fe73.9Nb3.1Cu0.9Si13.2B8.9 thin films have been produced by ion beam sputtering with two different beam energies (500 and 1000 eV). Magnetic measurements indicate that the samples display a uniaxial magnetic anisotropy, especially for samples prepared with the lower beam energy. Magnetization relaxation has been measured on both films with an alternating gradient force magnetometer and magneto-optical Kerr effect. Magnetization relaxation occurs on time scales of tens of seconds and can be described with a single stretched exponential function. Relaxation intensity turns out to be higher when measured along the easy magnetization axis. [ABSTRACT FROM AUTHOR]

The simple binary compound, MgB[sub 2], has created enormous excitement, due to its remarkably high T[sub c] (39 K), its exotic electronic and phononic structure, as well as its potential technological application. However, contrary to the initial expectation, worldwide efforts to enhance the T[sub c] of this material by means of chemical doping and applying hydrostatic pressure have failed. Investigations of other diborides or related materials have also resulted in finding of lower T[sub c]'s. In this letter we report a slight, but significant enhancement of T[sub c] in MgB[sub 2] films grown on boron crystals, which may stem from tensile-type strain. This finding opens up a new possibility for further optimizing T[sub c] in MgB[sub 2] and perhaps in related materials. © 2001 American Institute of Physics. [DOI: [10.1063/1.1427157]. [ABSTRACT FROM AUTHOR]