Crystal Growth of Bulk YBCO Superconducting Oxides; Effect of Undercooling

100

Y-Ba-Cu-O superconductors were prepared by the top-seeded melt growth process with multiseeding technique. By using several seeds at the same time, large samples could be fabricated in a short time with simple heat treatment. However, the samples fabricated by the normal multiseeding technique show a rapid decrease of trapped magnetic field value across the grain boundaries because of the residual liquid layer. To remove the residual liquid layer, various types of multiseeding were newly suggested. The optimum result was obtained when the seeds were arranged without spacing. The individual grains were combined as a single domain and did not show any deterioration of magnetic properties at the boundary. The formation mechanism of a well-combined single domain by the multiseeding technique is discussed.

“…To prepare a single-domained sample of 2 cm × 2 cm size, around 100 h is required only for the undercooling step, although this is variable, depending on the parameters [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Top-seeded melt growth of Y-Ba-Cu-O superconductor with multiseeding

Jee

Kim

Sung

et al. 2000

100

“…There are two different ways to fabricate the single grain YBCO samples, slow cooling [1,9,[11][12][13][21][22] and undercooling [5,23,24]. The quality of the grown Y123 grains strongly depends on the growth rate of the Y123 grain.…”

Section: Top-seed Melt Growth Processmentioning

confidence: 99%

“…The disadvantage of the slow cooling method is that the degree of T varies continuously as the temperature decreases during heat treatment, which results in inhomogeneous grain quality, especially the Y211 distribution in 123 grains. In the case of the undercooling technique, holding at a constant temperature replaces continuous slow cooling [5,23,24]. It results in a constant growth rate and better crystal homogeneity.…”

Section: Two Step Undercoolingmentioning

confidence: 99%

Variables affecting the fabrication of single grain YBa₂Cu₃O_7-ysuperconductors by the top-seeded melt growth process

Kim

Jee

Hong

2000

In this article, we summarize the variables affecting the fabrication of a single grain YBCO superconductor by a top-seeded melt-growth-(TSMG-) process. The important variables are the seed melting and the resolidification which lead to the formation of undesirable subsidiary Y123 grains at the seeded area, and nucleation at both the compact/substrate interfaces and compact surfaces. The undesirable Y123 nucleation acts as the main obstacles for the fabrication of the single grain Y123 superconductor because of its competitive growth with the Y123 grain grown from the seed. The methods of suppressing the formation of the subsidiary Y123 nucleation, and of shortening the entire processing time of the TSMG process were suggested.

“…Top-seeded melt growth (TSMG) [1,2], i.e. the combined technique of seeding and melt-growth, has been widely adopted to prepare well-oriented large single-domained YBa 2 Cu 3 O 7−y (Y123) crystal [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. SmBa 2 Cu 3 O 7−y (Sm123) and NdBa 2 Cu 3 O 7−y (Nd123) quasi-single crystals, whose melting points are higher than that of a Y123 phase, are generally used as seed materials to provide an artificial growth site.…”

Section: Introductionmentioning

confidence: 99%

Dissolution of seed crystals during top-seeded melt growth of

Jee¹,

Hong²,

Kim³

et al. 1998

During top-seeded melt growth processing of (Y123), dissolution of (Sm123) seed crystals was observed at temperatures below the melting point of the seed material. The dissolution was dependent on factors such as the seeding method (cold seeding or hot seeding), the holding temperature and the composition of the seed and compact. Applying the hot seeding method, lowering the seeding temperature and using (Sm211) excessive Sm123 seed and (Y211) excessive Y123 compact decreased the dissolution rate of the seed crystal, resulting in a well-grown Y123 single crystal. The dissolution behaviour of the Sm123 seed was explained in terms of the solubility of samarium in the liquid and the dissolution kinetics at the seed/liquid interfaces.