Title :
Synthesis of Hg-Re-Ba-Ca-Cu-O superconductors by a two-step method
Author :
Wolters, C. ; Amm, K.M. ; Knoll, D.C. ; Peterson, S.C. ; Schwartz, J.
Author_Institution :
Nat. High Magnetic Field Lab., Florida State Univ., Tallahassee, FL, USA
fDate :
6/1/1997 12:00:00 AM
Abstract :
A new two-step method has been developed to synthesize (Hg,Re)Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ with lower annealing temperatures as compared to conventional methods using a precursor which contains the (Hg,Re)Ba/sub 2/CaCu/sub 2/O/sub y/ phase. In the first step, high phase purity (Hg,Re)Ba/sub 2/CaCu/sub 2/O/sub y/ superconductors are prepared from commercially available Ba/sub 2/CaCu/sub 2/O/sub y/ precursors, HgO, and Re/sub 2/O/sub 7/. In the second step, the finely ground (Hg,Re)Ba/sub 2/CaCu/sub 2/O/sub y/ is mixed with Ca-Cu-O and HgO. This precursor mix is encapsulated in evacuated quartz tubes and annealed for 8 to 48 h between 750/spl deg/C and 850/spl deg/C. The resulting samples have (Hg,Re)Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ as a majority phase and exhibit a critical temperature of 133 K as prepared. The superconducting grains are platelike and randomly oriented. The grain sizes depend on the annealing time and temperature and reaches up to 30 /spl mu/m diameter and 5 /spl mu/m thickness. Second phases are mainly unreacted Ba/sub 2/CaCu/sub 2/O/sub y/ and Ca-Hg-O.
Keywords :
annealing; barium compounds; calcium compounds; grain size; high-temperature superconductors; mercury compounds; powder technology; rhenium compounds; superconducting transition temperature; 133 K; 750 to 850 degC; 8 to 48 hr; Ba/sub 2/CaCu/sub 2/O/sub y/ precursors; HTSC; Hg-Re-Ba-Ca-Cu-O; Hg-Re-Ba-Ca-Cu-O superconductors; annealing temperatures; critical temperature; grain sizes; precursor mix; superconducting grains; synthesis; two-step method; Annealing; Conducting materials; Encapsulation; High temperature superconductors; Laboratories; Land surface temperature; Magnetic fields; Mercury (metals); Superconducting materials; Superconductivity;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
