Harlan James Brown-Shaklee

Thermal conductivity of nano-grained SrTiO3 thin films

We measure the thermal conductivities of nano-grained strontium titanate (ng-SrTiO3) films deposited on sapphire substrates via time-domain thermoreflectance. The 170 nm thick oxide films of varying grain-size were prepared from a chemical solution deposition process. We find that the thermal conductivity of ng-SrTiO3 decreases with decreasing average grain size and attribute this to increased phonon scattering at grain boundaries. Our data are well described by a model that accounts for the spectral nature of anharmonic Umklapp scattering along with grain boundary scattering and scattering due to the film thickness.

Optical anisotropy near the relaxor-ferroelectric phase transition in lanthanum lead zirconate titanate

We examine the optical activity, birefringence, and transparency of Lanthanum-doped, lead zirconate titanate (PLZT 7/65/35) bulk ceramic wafer sections over visible and near-IR spectra and on heating. Optical transitions are compared to both crystallographic (rhombohedral-cubic) and domain (relaxor-ferroelectric) transitions identified with x-ray diffraction, dielectric, and calorimetry measurements. Optical activity and birefringence are shown to be enhanced for disordered domains near room temperature, to attenuate above the relaxor-ferroelectric transition and to gradually decay above the Curie point regardless of the initial poling state. The results are interpreted in light of the change of crystallographic symmetry due to the local strains induced by ferroelectric architecture. The heterogeneous local strains more strongly influence the optical properties than the macro-scale structure of the polycrystalline PLZT ceramic. This mechanism is significant for understanding optical rotation and birefring...

Oxygen partial pressure dependence of thermoelectric power factor in polycrystalline n-type SrTiO3: Consequences for long term stability in thermoelectric oxides

The Seebeck coefficient and electrical conductivity have been measured as functions of oxygen partial pressure over the range of 10−22 to 10−1 atm at 1173 K for a 10% niobium-doped SrTiO3 ceramic with a grain size comparable to the oxygen diffusion length. Temperature-dependent measurements performed from 320 to 1275 K for as-prepared samples reveal metallic-like conduction and good thermoelectric properties. However, upon exposure to progressively increasing oxygen partial pressure, the thermoelectric power factor decreased over time scales of 24 h, culminating in a three order of magnitude reduction over the entire operating range. Identical measurements on single crystal samples show negligible changes in the power factor so that the instability of ceramic samples is primarily tied to the kinetics of grain boundary diffusion. This work provides a framework for understanding the stability of thermoelectric properties in oxides under different atmospheric conditions. The control of the oxygen atmosphere ...

Fabrication of Wound Capacitors Using Flexible Alkali-Free Glass

Alkali-free glasses, which exhibit high energy storage densities (~35 J/cc), present a unique opportunity to couple high temperature stability with high breakdown strength, and thus provide an avenue for capacitor applications with stringent temperature and power requirements. Realizing the potential of these materials in kilovolt class capacitors with >1 J/cc recoverable energy density requires novel packaging strategies that incorporate these extremely fragile dielectrics. In this paper, we demonstrate the feasibility of fabricating wound capacitors using 50-μm-thick glass. Two capacitors were fabricated from 2.8-m-long ribbons of thin (50 μm) glass wound into 125-140-mm-diameter spools. The capacitors exhibit a capacitance of 70-75 nF with loss tangents below 1%. The wound capacitors can operate up to 1 kV and show excellent temperature stability to 150 °C. By improving the end terminations, the self-resonance can be shifted to above 1 MHz, indicating that these materials may be useful for pulsed power applications with microsecond discharge times.

Fabrication of Solid-State Multilayer Glass Capacitors

Alkali-free glasses show immense promise for the development of high-energy density capacitors. The high breakdown strengths on single-layer sheets of glass suggest the potential for improved energy densities over existing state-of-the art polymer capacitors. In this paper, we demonstrate the ability to package thin glass to make solid-state capacitors. Individual layers are bonded using epoxy, leading to capacitors that exhibit stable operation over the temperature range −55 °C to +65 °C. This fabrication approach is scalable and allows for proof testing individual layers prior to incorporation of the stack, providing a blueprint for the fabrication of high-energy density capacitors.

X-ray powder diffraction study of La2LiTaO6

The structure of La 2 LiTaO 6 has been derived from the powder X-ray powder diffraction (XRD) data. La 2 LiTaO 6 is monoclinic with unit-cell parameters a = 5.621(1) A, b = 5.776(1) A, c = 7.954(2) A, β = 90.34(2)°, space group P 2 1 / n (14), and Z = 2. The structure of La 2 LiTaO 6 is an ordered perovskite with alternating Li and Ta octahedra. A new set of powder XRD data ( d -spacing and intensity listing) has been generated to replace entry 00-039-0897 within the Powder Diffraction File. The newly elucidated structural data for La 2 LiTaO 6 shall facilitate quantitative analysis of this impurity phase which is often observed during synthesis of the fast-ion conductor phase Li 5 La 3 Ta 2 O 12 .