In-Situ Processing of Epitaxial and Textured High Tc Superconducting Hoba 2 Cu 3 O 7 . X Thin Films By Pulsed Laser Evap
- PDF / 642,224 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 99 Downloads / 153 Views
IN-SITU PROCESSING OF EPITAXIAL AND TEXTURED HIGH Tc SUPERCONDUCTING HoBa 2 Cu307.x THIN FILMS BY PULSED LASER EVAPORATION TECHNIQUE C. B. Lee, R. Prasad, A. K. Singha, S. Sharan, R. K. Singh, P.Tiwari and J. Narayan Dept. of Materials Science and Engineering N.C.State University Raleigh, N.C. 27695-7916 0. W. Holland and L. A. Boatner Solid State Divison OakRidge National Laboratory OakRidge, TN 37831
ABSTRACT Excellent quality epitaxial and textured superconducting HoBa 2 Cu3 07_, (Ho 123) thin films have been fabricated on lattice matched (100) KTaO 3 and (100) LaAIO 3 , and lattice mismatched (100) MgO substrates by the pulsed laser evaporation (PLE) technique. A bulk Ho123 target was evaporated using nanosecond excimer laser pulses with the evaporating material depositing on a substrate maintained in the temperature range of 5506500C. The temperature for zero resistance for HoBa2 Cu3 O7 -, films deposited on various substrates at 650'C varied between 85 to 89K. The epitaxial films deposited on (100) LaAlO 3 substrates exhibited critical current 2
densities greater than 3.5 x 106 Amps/cm at 77 K. The superconducting properties of the Ho 123 films were found to be similar to Y123 films. INTRODUCTION 3 3 The higher magnetic moment of holmium in the 123 phase (10.6, 0 l'B for Ho+ , y+ , respectively)[t] in comparison to yttrium has led to conjectures that the properties of HoBa2 Cu3 07.x superconductors may be different from YBa 2 Cu3 o 7 .x superconductors. High critical current density HoBa 2 Cu3 OTx films have been 7 fabricated on (100) MgO substrates by ff magnetron sputtering followed by ex-situ annealing at 900'C [4]. In this paper, we report and analyze the properties of HoBa 2 Cu3 O7Tx films formed by the biased in-situ pulsed laser deposition (PLE) technique with the maximum substrate temperatures ranging between 500 and 650'C. The films were deposited on lattice matched (100) LaA103, (100) KTaO3 , and lattice mismatched (100) MgO substrates. The important considerations for epitaxial film growth are the crystalline structure and the lattice parameter of the substrate. HoBa 2 Cu 3 0 7 has an orthorhombic structure (a - 3.82 A, b =3.89 A and c - 11.67
A) while MgO
and KTaO 3 are cubic and LaAIO 3 is rhombohedral with a = 4.20, 3.99 and 3.79 A, respectively.
EXPERIMENTAL The experimental setup is similar to deposition of YBa 2 Cu 3 O7 _x film, except that a Ho 123 target was 2
used. An excimer laser (X =308 nm, T =-45 nanoseconds) operating at an energy density of 2-2.5 J/cm was used to evaporate the bulk Ho 123 target, and the evaporated material was deposited on a substrate heated between 5006500C. [3,5]. The whole assembly was placed in an evacuated chamber with an oxygen partial pressure of 200 millitorr. The evaporated plume was green in color in contrast to the reddish blue color observed in the case of evaporation of Y123 targets. The nature and the dynamics of the PLE deposition process have been discussed in detail elsewhere[5]. RESULTS AND DISCUSSION Fig. 1 shows a resistance vs. temperature
Data Loading...
