Mitsunori Sato

Growth and superconducting properties of Bi2Sr2CaCu2O8+δ single-crystal whiskers using tellurium-doped precursors

Bi2Sr2CaCu2O8+δ (Bi2212) single-crystal whiskers were grown by annealing sintered Te-doped Bi–Sr–Ca–Cu–O precursors that had not passed through a melt-quenched glassy state, a process that is known well at this time. The optimum nominal composition of precursors is Ca-rich Bi2Sr2Ca2Cu2Te0.5Ox with a Te content of 0.5. The whiskers contain no Te element. The precursors are mainly composed of Bi2212 and (SrCa)3TeO6 (STO) phases. The STO or the element Te acts as a catalyst in enhancing whisker growth. The critical current (Ic) with a multibranched structure of the current–voltage characteristics due to the intrinsic Josephson junctions along the c axis is quite uniform, showing that the whiskers are homogeneous and of good quality.

Growth and Superconductivity of (BiPb)2Sr2Ca2Cu3O10+δ Single-Crystal Whiskers

(BiPb)2Sr2Ca2Cu3O10+δ ((BiPb)2223) single-crystal whiskers with a length of about 2 mm were grown by annealing a sintered Te-doped (BiPb)2Sr2Ca2Cu3Ox precursor pellet. The pellet was formed by mixing single-phase (BiPb)2223 with TeO2; the content ratio of TeO2 to Bi2223 was 0.5. For the growth, it is very important to use (BiPb)2223 single-phase powder as a precursor. The whiskers contain no Te and their composition is Ca-rich (BiPb)2(Sr0.3Ca0.7)4Cu3Ox. The whiskers have excellent crystallinity and a critical temperature of about 106 K. The critical current, which exhibits a multibranched structure in the current–voltage characteristics due to the intrinsic Josephson junctions along the c-axis, is quite uniform, showing that the whiskers are homogeneous and of good quality.

Superconducting properties of single-crystal whiskers of (Y0.86Ca0.14)Ba2Cu3Ox grown from precursors containing calcium and tellurium

Single-crystal whiskers of YBa2Cu3Ox (Y-123) phase with a length of about 2.5 mm were grown from sintered precursor powders with a nominal composition of Y1Ba2Cu3Te0.5Ca1.0Ox. Electron probe microanalysis analyses showed that the whiskers contain Ca but no Te with a composition of (Y0.86Ca0.14)Ba2Cu3Ox in which 14%Y is substituted by Ca. The precursor powder is composed of Ca-doped Y-123 and (BaCa)3TeO6 phases. The presence of the (BaCa)3TeO6 plays an important role in enhancing the growth of the whiskers. The whiskers show a critical temperature Tc of about 83 K and a critical current density, Jc of 4.4×104 A/cm2 at 82 K and self-field along the c axis. The whiskers exhibit interesting intrinsic Josephson effects along the c axis.

Properties of Czochralski‐grown RAIO3 (R: Dy, Ho, and Er) single crystals for magnetic refrigeration

Magnetization of RAlO3 (R: Dy, Ho, and Er) single crystals along the c axis have been measured by the superconducting quantum interference device magnetometer. The single crystals are nominally pure and large sized, grown by the Czochralski method. Paramagnetic properties depend on the rare‐earth elements. According to the magnetic entropy change, ErAlO3 single crystals are promising materials for the magnetic refrigerants using the Carnot cycle in the temperature range below 20 K.

Czochralski growth of Gd3(Ga1-xAlx)5O12 single crystals

Abstract Single crystals of Gd 3 (Ga 1- x Al x ) 5 O 12 with x =0.1−0.4 have been grown by the Czochralski method. They were colorless and transparent, and about 30 mm in diameter and 60 mm in length. The lattice parameters decreased linearly with increasing aluminum concentration, x , and varied from 12.354A( x =0.1) to 12.260A( x =0.4). The distribution coefficients of the aluminum ions varied from 1.14 ( x =0.1) to 1.07 ( x =0.4).

Effect of magnetic field strength in melt-processing on texture development and critical current density of Bi-oxide superconductors

Abstract Vertical magnetic fields up to 15 T were applied to the magnetic melt-processing (MMP) of Bi2212 bulks and Ag-sheathed tapes with a core thickness above 80 μm, which were set horizontally. Texture with the c -axis along the direction of magnetic field applied during MMP is developed due to the anisotropy in magnetic susceptibility of Bi2212. The degree of texture and the anisotropy factor in magnetization increase almost linearly as the magnetic field strength H a during MMP is increased. The anisotropy factor in magnetization reaches 6.5 at a H a of 13 T for Ag-doped Bi2212 bulks, whereas for Bi(Pb)2212 in which Pb partially substitutes for Bi the factor is suppressed to a half of that of Ag-doped Bi2212. The transport critical current I c and the critical current density J c of Bi2212 tapes also increase with increasing H a due to the texture development and I c reaches above 1000 A in self-filed for the tapes with a core thickness of 180 μm. However, for further thicker tapes, I c decreases. The suppressions in the I c for the tapes and in the anisotropy factor in magnetization for Bi(Pb)2212 bulks are due to inhomogeneous melting, and inhomogeneous nucleation and growth of crystals during MMP. When crystal growth is restricted, crystal alignment is suppressed.

Microstructure and critical current density of Bi2212 tapes grown by magnetic melt-processing

Abstract Vertical magnetic fields up to 9 T were applied to the magnetic melt-processing (MMP) of dip-coated and Ag-sheathed Bi2212 mono-core tapes with a core thickness of about 150 μm, which were set horizontally. SEM observation shows that a uniform high-degree of texture is formed throughout the thickness of the tapes by the magnetic field H a during MMP, whereas a large portion of the area is non-textured without H a . The critical current density J c of the tapes increases with increasing H a up to about 6 T due to the texture development. However, when H a >6 T some disturbance in J c appears; one is increased and the other is decreased. This may be due to the change of O 2 atmosphere around the tapes during MMP, which comes from the change of O 2 gas flowing by the magnetic field. The results suggest that a high magnetic field is very effective to enhance the texture development and to fabricate tapes with high critical current I c .

Single crystal growth and characterization of (Dy1−xGdx)3Ga5O12 Garnets

Single crystals of (Dy1−xGdx)3Ga5O12 (0<x<1) pseudo-binary garnets have been grown by the Czochralski method. They were homogeneous with good quality, about 25 mm in diameter and 50 mm in length. The lattice parameter increases with increasing gadolinium concentration. In the crystals, stress-birefringence due to dislocations was rarely observed under crossed nicols. The spiral growth occurs during the crystal growth, and tends to be suppressed by increasing gadolinium concentration. The spiral growth is likely to be affected by an asymmetric faceting growth.

Growth and electrical transport characteristics of Bi2Sr2Ca1Cu2Ox and Bi2Sr2CuOx single-crystal whiskers using tellurium-doped precursors

Abstract Bi 2 Sr 2 CaCu 2 O x (Bi2212) and Bi 2 Sr 2 CuO x (Bi2201) single-crystal whiskers were grown by annealing sintered Te-doped Bi–Sr–Ca–Cu–O precursors. The growth of Bi2212 or Bi2201 whiskers definitely depends on the Ca content of precursors; the optimal composition is Ca-rich Bi 2 Sr 2 Ca 2 Cu 2 Te 0.50 O x for Bi2212 and Bi 2 Sr 2 CaCuTe 0.50 O x for Bi2201. In the precursors Te ions exist in the phase of (SrCa) 3 TeO 6 . The whiskers contain no Te element. The Bi2212 whiskers have a critical temperature of about 80 K and the critical current with a multibranched structure of the current–voltage characteristics due to the intrinsic Josephson junctions along the c -axis is quite uniform, showing that the whiskers are homogeneous and of good quality. The Bi2201 whiskers show semiconducting resistance with no superconducting transition down to 4.2 K.

Growth of R-123 Phase Single Crystal Whiskers

Single-crystal whiskers of R1Ba2Cu3Ox (R-123, R = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) phase have been successfully grown by the Te- and Ca-doping method. The whiskers were grown from precursor pellets at just below their partial melting (peritectic) temperatures. The nominal composition of the R-123 whiskers is R1+uBa2+vCawCu3Ox (u+v+w=0, w>0) with R and/or Ba sites being substituted by Ca. However, the amount of Te was less than the analytical limit. The critical temperatures of the R-123 whiskers were around 80 K, and among these whiskers those with larger R ionic radii such as Dy, Gd, Eu and Sm require post-annealing in an oxygen atmosphere.