Investigation of the R2Se3-Cu2Se-In2Se3 (RÂ =Â La, Pr, Y and Er) systems at 870Â K and crystal structure of the R2CuInSe5 (RÂ =Â La, Ce and Pr) compounds

Phase equilibria in R2Se3-Cu2Se-In2Se3 (R = La, Pr, Y and Er) systems at 870 K were determined using X-ray powder diffraction. The existence of the RCuSe2 (LaCuS2 structure type, space group P21/c) and La5Cu13Se14 (unknown structure) compounds was confirmed in the R2Se3-Cu2Se (R = La, Pr) sections. The formation of the solid solutions R(2+x)/3Cu2−xSe2 (0 ≤ x ≤ 1) (Er2/3Cu2S2 structure type, space group P3¯) and the ErCu5Se4 compound with unknown structure was confirmed in the R2Se3-Cu2Se (R = Y, Er) sections. The existence of the La3In1.67Se7 (Ce3Al1.67S7 structure type, space group P63) and La4In4.67Se13 (La4In4.72Se13 structure type, space group Pbam) compounds in the La2Se3-In2Se3 system and the Pr3InSe6 (Pr3InSe6 structure type, space group Pnnm) compound in the Pr2Se3-In2Se3 system was confirmed. No ternary compounds exist in the Er2Se3-In2Se3 and Y2Se3-In2Se3 sections. The formation of the CuInSe2, CuIn3Se5, CuIn5Se8, CuIn7Se11 and CuIn11Se17 compounds in the Cu2Se-In2Se3 section was observed. The crystal structure of new quaternary R2CuInSe5 (R = La, Ce and Pr) compounds (space group Pnma, a = 1.20382(6) nm, b = 0.41185(2) nm, c = 1.7556(1) nm (for La2CuInSe5), a = 1.19997(7) nm, b = 0.40855(2) nm, c = 1.7464(1) nm (for Ce2CuInSe5) and a = 1.1973(3) nm, b = 0.40649(9) nm, c = 1.7408(4) nm (for Pr2CuInSe5)) was determined.