Ba(Ga,Ta)(0.05)Ti0.90O3, a B-site dipole-like substituted material is investigated for structural phase transitions over the temperature range 30 to 900 degrees C using x-ray diffraction. Rietveld refinement of the data suggests the material to be Pm[GRAPHICS]m (cubic) from 200 to 900 degrees C, P4/mmm (tetragonal) from 30 to 200 degrees C with phases similar to those of BaTiO3 [12]. Average grain size determined using scanning electron microscopy is 650nm. Measurements of dielectric properties from -50 to 120 degrees C and over a frequency range of 10Hz to 2MHz show a relatively flat dielectric constant that is electric-field tunable indicating that Ba(Ga,Ta)(0.05)Ti0.90O3 is a reasonable candidate for frequency agile components.

The employment of judicious substitution on B-sites in the perovskite oxide, BaTiO 3 , has yielded materials suitable for relatively temperature insensitive electric field tunable microwave devices. The properties, single-phase cubic perovskites with tunabilities as large as 30% at 1 V/μm and room temperature that possess low temperature coefficient of dielectric constant and tunability over the majority of the military specified temperature range, -55 to 125 °C, have been achieved in the charge compensated system Ba 1-x Sr x Ti 1–2y C y D y O 3 where C is Ho, Er, Tm, Lu, Sc, Y, In and D is Ta, Sb with 0 ≤ X ≤ 0.2, and 0 < y ≤ 0.10.

An improvement in ferroelectric device technology has become possible through optimization of the properties of the ferroelectric materials used to make the devices. The improvements discussed herein impact true time delay line and phase shifter performance by enhancing control over dielectric constant and extending the temperature range of tunability and device operation. Figures of merit were obtained for substituted-Ba 1 m x Sr x TiO 3 materials which have lower, less varying dielectric constant and adequate, less varying tunability at 1 MHz over the mil spec ( m 50 °C to 100 °C) range. For the sample whose figure of merit varies the least, dielectric constant and losses at 20 GHz and room temperature are reported. Dielectric constant and losses at 1 kHz are discussed.

The effect that oxygen stoichiometry has on the physical properties of high critical temperature superconductors is well documented. For a general understanding of the conditions necessary for processing high critical temperature superconducting materials, phase equilibrium diagrams have been quite useful; however, such diagrams provide no information concerning the time required to oxygenate superconducting structures. In this paper, we present experimental results that clearly demonstrate the relationships among phase equilibrium diagrams, oxygen diffusion coefficients and grain sizes with the time required to “adequately” oxygenate high critical temperature superconducting materials and device structures. While oxygen processing of the high critical temperature superconductor, YBa2Cu3O7−δ, is emphasized throughout this paper, the concepts and relationships discussed herein, in general, can be applied to the oxygen processing of other high critical temperature superconductors including the Hg and TI based systems.

In the search for lower dielectric constant substrates for use in a high critical temperature superconducting (HTSC) microwave technology, the dielectric constants and microwave loss tangents determined from the complex dielectric properties measured at 10 GHz and 300 K are reported for numerous perovskite antimonates like A/sub 2/MeSbO/sub 6/ where A=Ba or Sr, Me=a rare-earth, Y, Sc, Ga or In and A/sub 4/MeSb/sub 3/O/sub 12/ where A=Ba or Sr and Me=Li, Na or K. Using these material properties, the Clausius-Mossotti relationship and a nonlinear regression fitting program, the polarizability of Sb/sup 5+/ has been investigated and determined to be 1.18/spl plusmn/0.49 /spl Aring//sup 3/ which makes it an excellent candidate for use as a constituent in a HTSC microwave substrate technology.

A new substrate material LSAT, a 30/70 mole % solid solution between LaA103 and Sr2AITaO6, has been prepared for the purposes of eliminating twinning, strain and non-isotropic microwave properties found in pure LaA103 substrates. At 300 K and 30/70 mole %, LSAT is cubic with lattice parameter of 7.737 Å. The dielectric properties of single crystal LSAT (30/70 mole %) substrates have been measured at 10 GHz and 300 K and determined to be: dielectric constant ε=22.5; and, loss tangent tan(δ) ⩽ 10-3. High quality c -axis oriented high critical temperature superconducting (HTSC), YBa2Cu307-δ (YBCO), thin films have been deposited on (001) single crystal LSAT substrates. The crystal quality of these films is excellent as evidenced by the full width half maximum (FWHM) rocking curve widths of typically 300 arc-seconds. Critical current densities (as measured using magnetization) are about 4 × 106 A/cm2 at 10 K. Microwave film properties include an onset transition temperature (Tc) higher than 91 K, transition width (ΔTc) less than 5 K, surface resistance RS lower than copper (30 mω) at 85 K and 35 GHz for a film of thickness 2500 Å.

Compounds in the series A2MeSbO6 where A = Ba, Sr and Me = Sc, In and Ga have been used as substrate/buffer layers with YBa2Cu3O7−δ thin films. These materials were prepared by solid-state reaction of the oxides and carbonates The compounds are ordered perovskites except for Ba2InSbO6. All compounds are cubic except Sr2ScSbO6 and Sr2GaSbO6 which are pseudo-cubic, tetragonal. Dielectric constant and loss tangent are reported for each bulk compound. Herein is described the succesful deposition of thin films A2MeSbO6 on YBCO, A2MeSbO6/(00ℓ) YBCO/(100) MgO by pulsed-laser ablation.

A series of compounds in the system A4MeSbO12, where A=Ba, Sr and ME=Li, Na, and K, were prepared by solid state reaction at elevated temperature. A new form of strontium sodium antimonate (Sr4NaSb3Ol2) was prepared. The compounds that were prepared were characterized with regard to their lattice parameter, density and dielectric properties. Thin films were prepared by pulsed laser ablation deposition from dense targets, and epitaxial relationships identified between Yttrium barium copper oxide (YBCO) and these compounds.

We have studied the relative diffusion rates of oxygen through dielectric/buffer layers used in high critical temperature superconducting multilayer structures. Epitaxial bilayer films of dielectric (CeO2, LaGaO3, NdGaO3, LaAlO3, MgO, SrTiO3, LaLiTi2O6, or LaNaTi2O6) on YBa2Cu3O7−δ (YBCO) have been deposited onto (001) oriented single-crystal MgO substrates using pulsed laser deposition. These bilayers have been investigated for oxygen diffusion over the temperature range 350 to 650 °C by postdeposition annealing the films for 20 min in 0.5 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile the relative concentration of 18O to 16O in each bilayer. Compared to YBCO, the dielectrics MgO, SrTiO3, LaLiTi2O6, and LaNaTi2O6 are relatively slow diffusers, while CeO2, LaGaO3, NdGaO3, and LaAlO3 are relatively fast diffusers.

: Y124 can be heated to 850 deg C without serious O2 loss, and also Y123 loses O2 from its structure at temperatures above 400 deg C. Partial substitution of Ca for Y and of Li for Cu raised the transition temperature (Tc) and enhanced sintering in Y1 Ba2Cu4O8. We measured the critical temperature by two methods; a microwave technique (RF) which measures the surface resistivity at 35 GHz, and an AC technique which measures the magnetic screening provided by the whole sample. Twelve samples of Y124 or Y(1-z)Ca(z)Ba2Cu(4-x)Li(x)O8 were prepared; a summary is presented. It is desirable to have a thin film of Y124 for device applications; we have not been successful at this endeavor. jg

A series of compounds in the system A4MeSb13O12 where A=Ba, Sr and Me=Li, Na &K were prepared by solid state reaction at elevated temperature. A new form of Sr4NaSb3O12 was prepared. The compounds were characterized with regard to their lattice parameters, density and dielectric properties. Thin films were prepared by PLD from dense targets and epitaxial relationships identified between YBCO and these compounds.

We have studied the rate of oxygen diffusion through ytterbium oxide (Yb2O$3), a buffer and dielectric layer used in high critical temperature superconducting (HTSC) structures. An epitaxial bilayer film of Yb2O3 on YBa2Cu$3)O7-(delta ) (YBCO) was deposited onto an (001) oriented single crystal MgO substrate using the pulsed laser deposition technique. The rate of oxygen diffusion through the bilayer was investigated from 365 to 655 degree(s)C by post deposition annealing individual section of the bilayer in 0.5 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile 18O and 16O in each sample. Oxygen diffusion coefficients for Yb2O3 at 365, 465, 555 and 655 degree(s)C were determined to be roughly (6, 16, 360, and 200) X 10-1, respectively. For temperatures greater than about 500 degree(s)C, these diffusion rates can limit oxygen intake into underlying YBCO films; therefore, HTSC multilayer devices that utilize Yb2O3 as a dielectric layer may require longer annealing cycles in order to fully oxygenate each underlying HTSC layer.

In an effort to improve the high-frequency properties of bulk high-Tc superconductors, the surface resistivity was measured for a series of YBa2Cu3O7 samples with various levels of silver addition. The nominal weight percent of silver in the sample series ranged from 7.0% to 23.8%, and the sintering temperature varied from 860 to 930 °C. The surface resistivity was measured by cavity perturbation at frequencies of 8 and 35 GHz. While the addition of intergranular silver does improve the dc resistance for temperatures above the critical temperature Tc, the high-frequency surface resistivity for T