T. Claeson

Epitaxial growth and properties of YBa2Cu3Ox‐Pb(Zr0.6Ti0.4)O3‐YBa2Cu3Ox trilayer structure by laser ablation

We have grown YBa2Cu3Ox‐Pb(Zr0.6Ti0.4)O3‐YBa2Cu3Ox multilayer structure on SrTiO3 and Al2O3 substrates using laser ablation. The deposition conditions for the growth of trilayers and their properties are studied in this investigation. Scanning electron microscope images and x‐ray diffraction analyses indicate that all the constituent films in the trilayer grow epitaxially on SrTiO3 and were highly oriented on Al2O3. Transport measurements on these multilayers show that top YBa2Cu3Ox films have good superconducting properties.

Bi-epitaxial weak links based on YBa2Cu3O7- delta on NdGaO3

Thin epitaxial yttria-stabilized zirconia films were used as seed layers to form bi-epitaxial 45 degrees crystallographic boundaries in YBa2Cu3O7- delta films on (110) NdGaO3 substrates. The crystallographic alignment of the seed layer on the substrate and three different in-plane orientations (0 degrees , 9 degrees and 45 degrees ) of c-axis oriented YBa2Cu3O7- delta films on the (100) plane of yttria-stabilized zirconia were analysed. The microwave and magnetic field responses of bi-epitaxial-based Josephson junctions were registered.

Dielectric permittivity dynamics of Ba1−x SrxTiO3 epitaxial films (x=0.75): Microstructure and depolarization effects

Trilayer epitaxial heterostructures including metal oxide electrodes (SrRuO3, 200 nm) and a sandwiched dielectric layer (Ba0.25Sr0.75TiO3, 700 nm) were grown by laser ablation on (001)LaAlO3 substrates. The maximum permittivity of the Ba0.25Sr0.75TiO3 layer (ɛ′/ɛ0≈3700) was obtained at TM=160 K and an external electric field E≈106 V/m. The ɛ′(T) dependence for the Ba0.25Sr0.75TiO3 layer in the paraelectric phase is well fitted by the Curie-Weiss relation, with the Curie constant and the Weiss temperature differing only insignificantly from the corresponding bulk values. The change in the permittivity of the Ba0.25Sr0.75TiO3 layer induced by the application of a ±2.5 V bias voltage to the electrodes reached as high as 85%. The electric-field dependence of the polarization retained clearly pronounced saturated hysteresis loops up to temperatures 10–15 K above TM.

Permittivity of BaTiO3 epitaxial films grown on the YBa2Cu3O7−δ(001) surface

The epitaxial heterostructures YBa2Cu3O7−δ and YBa2Cu3O7−δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7−δ are grown by the laser evaporation method on an LaAlO3(100) substrate. The permittivity of a BaTiO3 layer is approximately doubled (T=300 K) when a SrTiO3 thin layer is inserted between a ferroelectric layer and superconducting cuprate electrodes. A maximum in the temperature dependence of the permittivity for a barium titanate layer in the YBa2Cu3O7−δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7−δ heterostructure is shifted by 70–80 K toward the low-temperature range with respect to its location in the corresponding dependence for the BaTiO3 bulk single crystal. The bias voltage dependence of the permittivity for the BaTiO3 grown layers exhibits a clearly pronounced hysteresis (T=300 K). The superconducting transition temperature for the lower YBa2Cu3O7−δ electrode in a superconductor/ferroelectric/superconductor heterostructure considerably depends on the rate of its cooling after the completion of the formation process.

Dielectric response of Ba0.75Sr0.25TiO3 epitaxial films to electric field and temperature

The structure and dielectric parameters of the intermediate ferroelectric layer in the (001)SrRuO3 ∥ (100)Ba0.75Sr0.25TiO3 ∥ (001)SrRO3 heterostructure grown by laser ablation on (001)La0.294Sr0.706Al0.647Ta0.353O3 were studied. Tensile mechanical stresses accounted for the polar axis in the ferroelectric, being oriented predominantly parallel to the substrate plane. The remanent polarization in the Ba0.75Sr0.25TiO3 layer increased approximately linearly with decreasing temperature in the interval 320–200 K. The real part of the dielectric permittivity of the intermediate ferroelectric layer reached a maximum ɛ′/ɛ0=4400 at TM≈285 K (f=100 kHz). The narrow peak in the temperature dependence of the dielectric loss tangent for the Ba0.75Sr0.25TiO3 ferroelectric layer, observed for T<TM, shifted toward lower temperatures with decreasing frequency and increasing bias voltage applied to the electrodes.

Response of the electrical resistivity and magnetoresistance of La0.67Ca0.33MnO3 epitaxial films to biaxial compressive mechanical (001) or (110) strains

The behavior of the electrical resistivity and magnetoresistance of 40-to 120-nm-thick La0.67Ca0.33MnO3 films grown on differently oriented lanthanum aluminate substrates was studied. The cell volume in thin (40 nm) La0.67Ca0.33MnO3 films grown coherently on (001)LaAlO3 was found to be substantially smaller. Mechanical stress relaxation in biaxially strained La0.67Ca0.33MnO3 films is accompanied by an increase in the cell volume. The temperatures at which the electrical resistivity and magnetoresistance in biaxially strained La0.67Ca0.33MnO3 films were maximum can differ by 60–70 K from those observed in bulk single crystals.

Ten-fold tunability of the permittivity of Ba/sub 1-x/Sr/sub x/TiO/sub 3/ in epitaxial multilayers with (Y/Nd)Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta//

Dielectric properties of 400-600 nm thick epitaxial layers of SrTiO/sub 3/ and Ba/sub 0.9/Sr/sub 0.1/TiO/sub 3/, inserted between YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// or NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, were investigated as functions of temperature and electric field. The electric field response of the dielectric permittivity of the ferroelectric layer correlated with the Curie point and was considerably higher with Nd based than with Y based superconducting electrodes. Insertion of thin buffer layers improved the tunability and decreased the microwave losses of the Ba doped dielectric.

YBa2Cu3O7−δ/CeO2 heterostructures on sapphire R-plane

Abstract(001)YBa2Cu3O7−δ epitaxial films were prepared by laser ablation on

Growth and properties of NdGaO 3 /YBa 2 Cu 3 O 7-δ multilayer structures

(1\bar 102)Al_2 O_3