Introduction of nitrate groups in the “123” structure: The 82 K superconductor YCaBa 4Cu 5(NO 3) 0.3(CO 3) 0.7O 11

Abstract

The introduction of nitrate groups in the “123”-type matrix has been performed for the first time. A new superconductor, YCaBa 4Cu 5(NO 3) 0.3(CO 3) 0.7O 11 with a T c onset of 82 K and a Meissner volume fraction of 15% at 4.2 K has been synthesized. The X-ray diffraction and electron diffraction study shows that its orthorhombic cell corresponds to a superstructure of YBa 2Cu 3O 7 with “2a 123×b 123×2c 123” , the subcell parameters are a 123=3.879(1) A ̊ , b 123=3.885(1) A ̊ , c 123=11.536 (3) A ̊ . HREM investigation shows that its structure is derived from the YBa 2Cu 3O 7 structure by replacing one row of CuO 4 groups (Cu1) out of two by a mixed row of NO 3 and CO 3 groups. The latter groups point one of their apices toward the adjacent row of CuO 4 groups, so that one observes rows of CuO 5 pyramids running along b . The superconducting properties of this phase, contrary to the oxycarbonate Y 1.6Ca 0.4Ba 4Cu 5CO 3O 11, are explained in terms of hte hole carrier density.