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

The polythermal section at a constant composition of 20 mol% BaCl2 of the q uasi-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 inc ongruent decomposition reactions of the quaternary phases Ba3Cu2O4Cl2 and B a2Cu3O4Cl2 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 meas ured at various temperatures. Both compounds contain two crystallographical ly different types of magnetic Cn atoms. Ba3Cu2O4Cl2 exhibits antiferromagn etic order with a Neel temperature T-N of about 20 K. A spin-flop transitio n is observed below T-N at a field of 2.6 T. Ba2Cu3O4Cl2 shows two antiferr omagnetic transition temperatures at T-NI approximate to 337 K and T-NII ap proximate to 33 K, Below T-NI some spontaneous magnetization is observed. ( C) 1998 Academic Press.