Q. Xiong

Fabrication of biaxially aligned YBa2Cu3O7−x thin films on glass substrates

Abstract Biaxially aligned YBa 2 Cu 3 O 7− x thin films have been fabricated on glass substrates with an in-plane aligned yttria-stabilized zirconia (YSZ) buffer layer. Ion-beam assisted pulsed laser deposition was used to prepare the YSZ buffer layers on amorphous glass substrates. The YSZ films deposited at room temperature exhibited (001) orientation, whereas at temperatures higher than 300°C, YSZ grew with high degree of (111) orientation. Both the (001) and (111) YSZ films were biaxially aligned. YBa 2 Cu 3 O 7− x films deposited using pulsed laser deposition on biaxially aligned (001) YSZ on glass were highly c -axis oriented and strongly a - b plane aligned. A critical temperature T c0 ( R = 0) of 87.1 K was routinely achieved and J c was in the range of ∼ 10 4 A/cm 2 . The limitation in J c was found to be due to microcracks in the YBCO film caused by the tensile stress resulting from the thermal expansion mismatch between the glass and YBCO. The results suggest that glass with a better thermal expansion match to YBCO would lead to higher J c values.

Y1BA2CU3O7-X MULTILAYER STRUCTURES WITH A THICK SIO2 INTERLAYER FOR MULTICHIP MODULES

For high temperature superconducting multichip modules and other related electronic applications, it is necessary to be able to fabricate several Y 1 Ba 2 Cu 3 O 7– x (YBCO) layers separated by thick low dielectric constant dielectric layers. In this work, we report the successful fabrication of YBCO/YSZ/SiO 2 (1–2 μm)/YSZ/YBCO multilayer structures on single crystal yttria stabilized zirconia (YSZ) substrates. In contrast to previously reported work, the top YBCO layer did not show any cracking. This is due to a technique that allows for stress relief in the SiO 2 layer before the second YBCO layer is deposited. The top YBCO layer in our multilayer structure had T c = 87 K and J c = 10 5 A/cm 2 (at 77 K), whereas the bottom YBCO layer had T c = 90 K and J c = 1.2 × 10 6 A/cm 2 (at 77 K). We also showed that the quality of the bottom YBCO layer was preserved during the fabrication of the multilayer due to the annealing process during which O 2 diffused into the YBCO, replacing the O 2 lost during the deposition of the top YBCO layer.

Epitaxial Tl2Ba2CaCu2O8 superconducting thin film on Sr2(AlTa)O6 buffer layer

Epitaxial Tl2Ba2CaCu2O8 superconducting films have been successfully grown on the dielectric Sr2(AlTa)O6 (SAT) buffer layers. X‐ray diffraction data showed that the films were highly c‐axis oriented with a rocking curve full width half maximum as narrow as 0.3°. The films also had an excellent in‐plane epitaxy with Tl2Ba2CaCu2O8[100] aligned with SAT[100] and MgO[100] of the substrate. The zero resistance temperature Tc of the superconducting films ranged from 95 to 103 K and the transport critical current density Jc in zero field was 3×105 A/cm2 at 77 K.

Synthesis and start cation-composition of HgBa2CuO4+δ

Abstract The synthesis conditions of HgBa 2 CuO 4 + δ were studied. It was observed that the best phase purity was achieved at an apparent cation ratio of Hg:Ba:Cu = 0.7:2:1 that was obtained by either Hg deficient initial compositions or extra Hg absorbents, e.g. Au foil. No significant impurities or site mixing can be identified by X-ray/neutron powder diffraction investigations in these non-stoichiometric samples. However, their large paramagnetic background suggests the existence of (Ba, Cu) oxides. Our data also show that this apparent Hg deficiency is likely to be synthesis-reaction related.

Hg deficiency and phase segregation in HgBa2CuO4+δ

Abstract HgBa2CuO4+δ (Hg-1201) samples synthesized with various initial compositions and at different Hg vapor pressures were examined by SEM, TEM, EDS and X-ray diffraction. The results suggest that Hg-1201 is intrinsically a Hg non-stoichiometry phase. The allowed Hg vapor pressure, which is limited by the competitions from HgBaO2, required an equilibrium defect density in the Hg site at synthesis temperatures. These defects correspond to a 30% Hg deficiency at ∼800°C with a balance Hg vapor pressure at the order of 10−1 atm. However, the equilibrium defect density should decrease with temperature, and is approximately zero at room temperature based on our EDS data. Therefore, cation diffusion, defect coarsening, and possible phase segragation occur during the cooling, which create various impurities and inclusions in the samples obtained. Further investigations on the related phase diagrams are needed to design a better synthesis procedure.

Magnetic field and temperature dependence of critical current densities in multilayer YBa2Cu3O7−δ films

In order to build high‐temperature superconductor (HTS) multichip modules (MCMs), it is necessary to grow several epitaxial layers of YBCO that are separated by thick dielectric layers without seriously affecting the quality of the YBCO layers. In this work, we have successfully fabricated YBCO/YSZ/SiO2/YSZ/YBCO structures on single‐crystal LaAlO3 substrates using a combination of pulsed laser deposition for the YBCO layers and ion‐beam‐assisted rf sputtering to obtain biaxially aligned YSZ intermediate layers. The bottom YBCO layer had a Tc∼89 K, Jc∼7.2×105 A/cm2 at 77 K, whereas the top YBCO layer had a Tc∼86 K, Jc∼6×105 A/cm2 at 77 K. The magnetic field and temperature dependence of Jc for the YBCO films in the multilayer have been obtained. The results for each of the YBCO layers within the YBCO/YSZ/SiO2/YSZ/YBCO structure are quite similar to those for a good quality single‐layer YBCO film.

Tl2Ba2CaCu2Oy superconducting thin films on polycrystalline Al2O3 substrates with textured YSZ buffer layers

Abstract We report for the first time the successful fabrication of Tl 2 Ba 2 CaCu 2 O y superconducting thin films on polycrystalline Al 2 O 3 substrates using yttria-stabilized-zirconia (YSZ) buffer layers. Ion beam-assisted laser deposition was used to obtain the textured YSZ buffer layers. The Tl 2 Ba 2 CaCu 2 O y thin films were shiny, highly c -axis oriented with respect to the film surface and strongly in plane textured. The zero resistance temperature of these films was as high as 108 K with a critical current density of ∼ 10 5 A/cm 2 at 77 K.

Improvement of in-plane alignment of YBa2Cu3O7−x films on polycrystalline alumina substrates using biaxially aligned CeO2/YSZ buffer layers

Abstract Biaxially aligned superconducting YBa 2 Cu 3 O 7−x thin films have been fabricated on ceramic alumina substrates. Yttria-stabilized zirconia buffer layers were first deposited on alumina using ion-beam assisted pulsed laser deposition. CeO 2 and YBCO films were subsequently deposited on the YSZ layer using pulsed laser deposition (PLD). All three layers were (001) oriented and biaxially textured. The YBCO films have T c values of 89 K and J c of 1×10 5 A/cm 2 at 77 K.

Fabrication techniques and electrical properties of YBa2Cu3O7−x multilayers with rf sputtered amorphous SiO2 interlayers

Abstract We have successfully fabricated YBa 2 Cu 3 O 7−x /YSZ/YBa 2 /YSZ/YBa 2 Cu 3 O 7−x multilayer structures on single crystal LaAlO 3 (100), substrates. The YBa 2 Cu 3 O 7−x (YBCO) layers were deposited using pulsed laser ablation (PLD), the biaxially aligned YSZ (250 nm thick) layers were deposited using ion beam assisted PLD (IBAD-PLD), and an amorphous SiO 2 (1–2μm) layer fabricated via rf sputtering was sandwiched between the YSZ layers. Fabrication techniques and characterization results are reported for patterned layers in this work.

Enhancement of critical current density in Tl2Ba2CaCu2Oy superconducting thin film on polycrystalline Al2O3 substrates using textured YSZ buffer layers

Abstract Tl 2 Ba 2 CaCu 2 O y superconducting thin films on polycrystalline Al 2 O 3 substrates with and without textured yttria-stabilized-zirconia(YSZ) or CeO 2 /YSZ buffer layers were fabricated. Ion beam-assisted laser deposition was used to obtain the textured YSZ buffer layers. The Tl 2 Ba 2 CaCu 2 O y thin films grown on the YSZ buffer layers were highly c-axis oriented with respect to the film surface and strongly in plane textured. The zero resistance temperature of these films was 100–108K. The critical current density (J c ) of the films grown on the YSZ buffer layers was 10 5 A/cm 2 . J c of the films grown on the CeO 2 /YSZ buffer layer or on Al 2 O 3 substrates directly was less than 10 4 A/cm 2 .