Y. Q. Tang

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.

Epitaxial Sr2(AlTa)O6 films as buffer layers on MgO for YBa2Cu3O7−x thin film growth

Sr2(AlTa)O6 thin films (2000–3000 A) have been deposited on MgO (001) substrates using pulsed laser deposition (PLD). X‐ray‐diffraction analysis shows that the Sr2(AlTa)O6 grows with the c axis highly oriented normal to the substrate plane and very good in‐plane epitaxy. The subsequently deposited YBa2Cu3O7−x films using PLD on Sr2(AlTa)O6 buffered MgO substrates exhibit excellent epitaxial growth with a narrow rocking curve width and a small φ scan peak width. The critical temperature Tc0 of 90–92 K has been achieved reproducibly and the critical current density is over 2.7×106 A/cm2 at 77 K.

Superconducting TlSr2(Ca,Cr)Cu2O7 thin films with critical current density up to 106 A/cm2

Superconducting TlSr2(Ca,Cr)Cu2O7 thin films with zero resistance temperature Tc up to 102 K and critical current density Jc as high as 106 A/cm2 at 77.7 K have been successfully prepared via laser ablation and thallium diffusion. Prolonged low temperature annealing in air was used for film processing. X‐ray diffraction patterns indicated that the films were highly oriented 1212 phase with c axes normal to the LaAlO3(100) or MgO(100) substrates.

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.

A new 1223-type high Tc cuprate (Tl, V) Sr2Ca2Cu3O9

A new 1223-type (Tl, V)-based superconducting layered cuprate (Tl1−xVx) Sr2Ca2Cu3O9 withx=0.25 and 0.50 has been successfully synthesized in the nearly-pure form and identified by powder X-ray diffration analyses. An excessive quantity of Tl is necessary for the preparation of the (Tl, V)-based 1223-type compound. Resistance and ac susceptibility measurements showed that the new (Tl, V)-based 1223 cuprate exhibits Tc above 110 K.

Synthesis and superconductivity of a new 1222-type T1-based layered cuprate (T1, Nb) Sr2(Nd, Ce)2Cu2O z

Synthesis and superconductivity of a new 1222-type layered cuprate (Tl1−xNbx) Sr2(Nd1−yCey)2Cu2Oz have been studied. The structure of this cuprate is directly related to that of Nb-1222 NbSr2(Nd, Ce)2Cu2Oz with tetragonal body-center lattice. Partial substitution of Tl for Nb in Nb-1222 phase improves its superconductivity. (Tl1−xNbx) Sr2(Nd0.75Ce0.25)2Cu2Oz samples prepared by the typical procedure exhibit superconductivity withTc of 30–40 K. Effects of Tl and Nb on superconductivity of this cuprate are briefly discussed.