Single crystal growth of cuprates from hydroxide fluxes
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Single crystal growth of cuprates from hydroxide fluxes S. A. Sunshine,a) T. Siegrist, and L. F. Schneemeyer Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (Received 3 May 1996; accepted 1 October 1996)
Barium and potassium hydroxide have been investigated as fluxes for the growth of cuprate single crystals. The relatively high solubility of transition metals and lanthanoids in these salt fluxes at moderate temperatures allows significant lowering of the growth temperatures required for many phases. Also, phases not stable at high temperatures become accessible. Two new cuprates have been prepared in the Ba –Ca–Cu–O and Ba–Y –Cu–O systems from a Ba(OH)2 ? H2 O flux. The compounds Ba3 (Y0.23 Cu0.77 )2 O5.78 and Ba3 (Ca0.24 Cu0.76 )2 O4.43 crystallize in a tetragonal (space group I4ymmm) oxygen deficient Sr3 Ti2 O7 -type structure with lattice parameters ˚ 4.022(1) A ˚ and c 21.61(2) A, ˚ 21.63(2) A, ˚ respectively. The a 4.069(2) A, compound (Ba0.92 Sr0.08 ) (Ca0.38 Cu0.62 )O2.1 crystallizes with a doubled perovskite unit cell ˚ In addition, single crystals of Ba2 YCu3 O72d have along all three axes, a 8.116(4) A. been prepared from a KOH flux at 750 ±C.
I. INTRODUCTION
The discovery of superconductivity in the Ba –Y– Cu–O system has led to a vast amount of work on this quaternary system. In addition to BaY2 CuO5 and the superconductor Ba2 YCu3 O7 , several other quaternary phases have been reported. The phase that is formed during the synthesis depends on the temperature, atmosphere, pressure, starting materials, and method of synthesis. The phases Ba3.2 Y0.8 Cu22x O6.42x 0.12 , x , 0.3,1 Ba8 Y3 Cu5 O17.51d ,2 Ba5 YCu2 O8.51d ,2 Ba4 YCu3 O8.51d ,3 and Ba8 YCu4 O162d 4 have been synthesized by traditional solid state reactions in air. In addition to synthesis using traditional solid state methods, there has also been a great deal of work on single crystal growth of Ba2 YCu3 O7 . The majority of this work has involved crystal growth from CuO-rich melts.5 Recently, Ba(OH)2 and Ba(OH)2yBaCl2 mixtures have been demonstrated to be useful fluxes for the growth of barium cuprates.6,7 In addition, KOH and NaOH have been demonstrated to dissolve rare-earth and alkaline-earth oxides and have been used as fluxes in the low temperature synthesis of La22x AEx CuO4 (AE Ca, Sr, Ba).8 Further, single crystals of Ba2 LnCu3 O7 (Ln Y, Nd, Sm, Eu, Gd ) have been grown from NaOH and KOH fluxes.9 Since many of the previous studies have involved the synthesis of phases accessible at temperatures greater than 900 ±C, we have explored the growth and characterization of phases in the Ba–Y–Cu–O system from Ba(OH)2 ? H2 O and KOH fluxes. Use of these fluxes allows for lower synthesis temperatures, thus stabilizing Cu31 , and could
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Present address: RAYCHEM, MS123y6614, 300 Constitution Drive, Menlo Park, California 94025.
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J. Mater. Res., Vol. 12, No. 5, May 1997
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