HIGH-PRESSURE SYNTHESIS AND SUPERCONDUCTIVITY OF SR-CA-CU-O-CL COMPOUNDS WITH 0212-TYPE AND 0223-TYPE STRUCTURE

We synthesized 02(n - 1)n-type Sr2Can-1CunOxCly (n = 2, 3) with their apical sites occupied by both oxygen and chlorine by a high-pressure t echnique without using a precursor. The n = 2 phase showed superconduc tivity below 83 K, while the T-c for the n = 3 phase was found to be 3 5 K. We examined the effects of oxygen partial pressure and Cl content on the phase formation by varying the nominal composition in starting materials. It was found that phases with a fewer number of CuO2 sheet s are formed, when samples are heated under higher oxygen pressure, wh ich is similar to the tendency observed in other homologous series of cuprates. The results of thermoelectric power measurements suggest tha t the as-synthesized n=2 phase is located in the underdoped region and the n=3 phase is much more underdoped than the n = 2 phase. (C) 1998 Elsevier Science B.V. All rights reserved.