SULFUR P-BAND HOLE GENERATION IN BETA-BACU2S2 - SYNTHESIS OF METALLICKXBA1-XCU2S2 FROM MOLTEN MIXED K-BA POLYSULFIDE SALTS

The reaction of Cu with molten mixed polysulfide K2-2xBaxSy flux produ ced KxBa1-xCu2S2 (0.1 < x < 0.4) at 450 degrees C. Crystal data for K0 .36Ba0.64Cu2S2 at 23 degrees C (Mo K alpha radiation): a=3.890(1) Angs trom; c=12.753(3) Angstrom; V=192.9(1) Angstrom(3); Z = 1; d(calc) = 5 .055 g cm(-3); space group I4/mmm (no. 139); 2 theta(max) = 80 degrees ; Mo K alpha radiation; number of data collected, 545; number of indep endent data, 307; independent data observed with I > 3 sigma(1), 196; number of variables, 8; mu = 187.02 cm(-1); final R=0.034; R(w)=0.047; goodness-of-fit=2.32. The structure is isomorphous to that of beta-Ba Cu2S2 (or the well-known ThCr2Si2 structure), with anti-PbO type [Cu2S 2] slabs and a statistical disorder between K+-Ba2+ ions. Substitution of K+ cation for Ba2+ gives rise to mixed valency and a p-type metall ic compound. Charge transport properties are reported.