Structure and X-ray reference diffraction patterns of (Ba_(6-x)Sr_x)R_2Co_4O_(15) (x= 1, 2) (R= lanthanides)

摘要

The structure and X-ray patterns of two series of barium lanthanide cobaltates, namely, Ba_4Sr_2/R_2Co_4O_(15) (R = La, Nd, Sm, Eu, Gd, and Dy), and Ba_5SrR_2Co_4O_(15) (R = La, Nd, Sm, Eu, and Gd) have been determined. These compounds crystallize in the space group Pb_3mc; the unit-cell parameters of Ba_4Sr_2/R_2Co_4O_(15) (R from La to Dy) decrease from a = 11.6128(2) A to 11. 5266(9) A, c = 6.869 03(11) to 6. 7630(5) A, and V=802.23(3) A~3 to 778.17(15) A~3, respectively. In the Ba_4SrR_2Co_4O_(15) series (R = La to Gd), the unit-cell parameters decrease from a= 11.735 44(14) A to 11.619 79(12) A, c = 6.942 89 (14) A to 6.836 52(8) A, and V= 828.08(3) A~3 to 799.40(2) A~3. In the general structure of (Ba_(6-x)Sr_x)R_2Co_4O_(15), there are four Co ions per formula unit occupying one CoO_6 octahedral and three CoO_4 tetrahedral units. Through corner-sharing of these polyhedra, a larger CO_4O_(15) unit is formed. Sr~(2+) ions adopt both octahedral and 8-fold coordination environment. R~(3+) ions adopt 8-fold coordination (mixed site with Sr), while the larger Ba~(2+) ions assume both 10-and 11-fold coordination environments. The samples were found to be insulators. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File (PDF).