Phase diagram investigations in the system Ba-Cu-O-Cl and magnetic properties of Ba3Cu2O4Cl2 and Ba2Cu3O4Cl2

摘要

The polythermal section at a constant composition of 20 mol% BaCl2 of the quasi-ternary system BaCl2BaO-CuOx was investigated at p(O-2) = 0.21 bar by means of DTA/TG and soaking experiments. Our results show the nature of incongruent decomposition reactions of the quaternary phases Ba3Cu2O4Cl2 and Ba2Cu3O4Cl2 at T = 925 degrees C (+/-5) and T = 975 degrees C (+/-5 degrees), respectively. Single crystals of both compounds were grown, Furthermore, field-dependent magnetic properties of Ba3Cu2O4Cl2 and Ba2Cu3O4Cl2 are measured at various temperatures. Both compounds contain two crystallographically different types of magnetic Cn atoms. Ba3Cu2O4Cl2 exhibits antiferromagnetic order with a Neel temperature T-N of about 20 K. A spin-flop transition is observed below T-N at a field of 2.6 T. Ba2Cu3O4Cl2 shows two antiferromagnetic transition temperatures at T-NI approximate to 337 K and T-NII approximate to 33 K, Below T-NI some spontaneous magnetization is observed. (C) 1998 Academic Press. [References: 19]