Sains Ma1aysiana 26(2): 15-26 (1997)                                                                                           Sains Fizis/

                                                                                                                                                                 Physical Sciences

Effects of Yttria Doping on Some Properties of

YBa₂Cu₃O_7-δ Superconductor

Mustaffa Hj. Abdullah & Tan Tuan Keat

Jabatan Fizik

Fakulti Sains Fizis & Gunaan

Universiti Kebangsaan Malaysia

43600 UKM Bangi Selangor D.E.

ABSTRACT

Samples of Y-Ba-Cu-O superconductor with nominal compositions of YBa₂Cu₃O_7-d + x (weight %) Y₂O₃ (x = 0 - 15) were prepared by solid state reaction method using the Y₂Cu₂O₅ and BaCuO₂ precursors as the starting reagents. The X-ray diffraction (XRD) diffractograms for the doped samples (x> 0) show an additional non-superconducting Y₂BaCuO₅ (211) phase. The scanning electron microscope (SEM) micrographs show that the smaller Y₂BaCuO₅ grains are precipitated on the surface of the larger YBa₂Cu₃O_7-d (YBCO) crystals. The grain size of the YBCO decreases with increasing yttria. The superconducting zero resistivity critical temperature (T_co) of the doped samples is very close to the T_co of the YBCO for x < 5, but it seems to be significantly decreasing for larger x. The transport critical current density (J) for x < 5 is enhanced due to magnetic flux pinning process by the 211 phase. However, J_c decreased for larger x due to the increase of weak links at the grain boundaries of the YBCO phase.

ABSTRAK

Sampel superkonduktor Y-Ba-Cu-O dengan komposisi nominal YBa₂Cu₃O_7-d  + x (% berat) Y₂O₃ (x = 0 -15) disediakan dengan kaedah tindakbalas keadaan pepejal menggunakan bahan pelopor Y₂Cu₂O₅ dan BaCuO₂ Difraktogram pembelauan sinar-X (XRD) bagi sampel yang didop (x > 0) menunjukkan wujudnya fasa tak mensuperkonduksi Y₂BaCuO₅ (211). Mikrograf mikroskop imbasan elektron (SEM) menunjukkan bahawa butiran Y₂BaCuO₅ yang lebih kecil itu termendap di atas permukaan hablur YBa₂Cu₃O_7-d yang lebih besar. Saiz hablur YBCO mengecil dengan peningkatan yittria. Suhu genting kerintangan sifar (T_c) bagi sampel yang didop adalah hampir dengan T_co bagi YBCO untuk x<5, tetapi menurun dengan agak cepat untuk x yang lebih besar. Ketumpatan arus genting angkutan (J) untuk x < 5 meningkat jika dibandingkan dengan YBCO disebabkan oleh proses kepinan fluks magnet oleh fasa 211. Walau bagaimanapun, J_c menurun untuk x yang lebih tinggi kerana meningkatnya hubungan lemah pada sempadan butiran fasa YBCO.

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