Growth of (Y_1−xCa_x)Ba₂Cu₄O₈in ambient pressure and its tri-axial magnetic alignment

Abstract

We report the growth of single crystals in ambient pressure and tri-axial orientation under modulated rotation magnetic fields (MRFs) for124 crystals approximately 50 μm in size have been successfully grown for x0.1 in a growth temperature region from 650 °C to 750 °C. Their critical temperatures increased with x and exhibited approximately 91 K for x=0.1. By applying an MRF of 10 T, pulverised powders of (Y 1−x Ca x )124 were tri-axially aligned in epoxy resin at room temperature in a whole x region below x=0.1. The magnitude relationship of the magnetic susceptibilities (χ) along crystallographic directions for (Y 1−x Ca x )124 was χ c >χ a >χ b at room temperature and was unchanged with a change in x. From changes in the degrees of the c-axis and the in-plane orientation (Δω) for the (Y 1−x Ca x )124 powder samples aligned under three different MRF conditions, it was found that MRFs above at least 1 T were required to achieve almost complete tri-axial alignment with Δω<5°. Irreversibility lines for H//c were successfully determined even from the powder samples by the introduction of magnetic alignment without using single crystalline samples. The present study indicates that magnetic alignment is a useful process for the fabrication of quasi-single-crystals from the perspective of solid-state physics and the production of cuprate superconducting materials.

Increasing theTcof YBa2Cu4O8to 90 K by Sr substitution via the KOH flux method

“…[22][23][24] These crystals even exhibit a higher T c than those prepared using other synthesis methods, 25,26) indicating higher crystalline perfection. Ca is easily doped into the Y124 crystal by adding Ca to the molten KOH solution, and the Ca-doped Y124 shows T c = 90 K. 22,28,29) These findings suggest that the KOH flux method can easily provide Sr-substituted Y124 crystals with high crystalline perfection.…”

“…This T c value is obviously higher than the previously reported T c of Sr-substituted Y124 and at the same level of Y124 with doped with 10 at% Ca that substitutes the Y site. [7][8][9][10]22,28,29) In the high-Sr-content region of x = 0.3-0.5, T c remains steady at a high value of 89 K. This remarkable T c increase indicates that Sr substitution strongly affects the electric state of crystalline Y124. The pristine Y124 phase with no Sr substitution shows a c-lattice parameter of 27.23 Å, which is the typical value of pure Y124 synthesized using conventional high-temperature, high-pressure methods, as shown in Fig.…”

“…11,20) Single crystals of Y124 and of Y124 with other rare-earth elements substituting for Y (RE124), have also been grown from molten hydroxide solutions at low temperatures ranging from 475 °C to 800 °C. [21][22][23][24][25][26][27][28][29] Y124 and RE124 crystals grown from molten KOH solutions show a sharp superconducting transition despite the low growth temperature of approximately 700 °C. [22][23][24] These crystals even exhibit a higher T c than those prepared using other synthesis methods, 25,26) indicating higher crystalline perfection.…”

Low-temperature liquid-phase epitaxy of YBa2Cu3Oy films by the molten KOH method

“…The nucleation of Y124 crystals was not seen on the LAO substrate, and the STO substrate melted above 550 °C because of the KOH flux. Furthermore, the in-field characterization of triaxially oriented Y124 powders prepared by the modulated rotation of magnetic fields was reported by Horii et al 22) [23][24][25] where the Y123 phase was stable at temperatures higher than that of the Y124 phase at constant oxygen partial pressure [ p(O 2 )]. Moreover, Y123 was stabilized at lower temperatures with decreasing p(O 2 ).…”

Linear drive type of modulated rotating magnetic field for a continuous process of three-dimensional crystal orientation

“…Substances with a triaxial magnetic anisotropy under the MRF that have sufficiently high orientation energy are biaxially aligned. In practice, biaxial magnetic alignment has been demonstrated in substances with an orthorhombic crystal structure such as RE 2 Ba 4 Cu 7 O y (RE: rare-earth element), 1),3),4),7) REBa 2 Cu 4 O 8 4)6), 8) and L-alanine. 2) Figure 1(a) shows a schematic of an intermittent type of MRF as an example.…”