Synthesis of a new copper oxide "In_0.3Cu _0.7Ba₂LaCu₂O_y" and characterization of its physical properties

Though we previously reported a copper oxide, InBa₂CuO _y with an a-axis length of 4.18Å, its electric property was insulating. Based on the assumption that the insulating property comes from the existence of the oxygen vacancy correlated with the extremely long a-axis length, shortening the a-axis length below 4.0Å was tried to diminish the oxygen vacancy. The compound that we expected is represented by In _xCu_1-xBa₂LnCu₂O_y (In1212). To prepare the In_xCu_1-xBa₂LnCu ₂O_y, various kind of lanthanoides revealing that the smallest amount of impurity phases was formed when Ln = La. With changing the In content, x in In_xCu_1-xBaLa₂Cu ₂O_y from 0.2 to 1.0, the least impurity was prepared when x was 0.3. The XRD pattern of In_0.3Cu_0.7Ba ₂LaCu₂O_y was refined by the Rietveld analysis, suggesting that the structure is tetragonal with a-axis length of3.91±0.03 Ǻ and a c-axis length of 11.81±0.09 Ǻ, and is similar in structure to LaBa₂Cu ₃O_y except the partial substitution of In for Cu(2) Its resistivity was semiconducting. After annealing in O₂, the resistivity was drastically decreased, but superconductivity was not observed above the temperature of 10K. According to the Hall effect measurement, the hole density of the oxygen-annealed sample was 7.9 × 10¹⁹ cm ^-3 at room temperature. While the ratio of itinerant holes v/p in the YBa₂Cu₃O_6.76 superconductor was as large as 100-200%, the ratio for In_0.3Cu_0.7Ba₂LaCu ₂O_y was 0.001% to 10%, suggesting that the majority of holes are maybe localized in the In,Cu(2) plane.