THE SYNTHESIS AND CRYSTAL-STRUCTURE OF NEW COMPOUND K6CRNB15O42

A new compound was found in the ternary system K2O-Cr2O3-Nb2O5, Chemic al analyses show that the compound formula is K6CrNb15O42. The structu re was solved using direct method and Fourier techniques; it crystalli zes in the hexagonal system with unit cell parameters a = 9.126(3) ang strom, c = 12.068(3) angstrom, V = 870.4(5) angstrom3, and space group P6(3)g/mcm, Z = 1. Of the 829 unique reflections measured by counter techniques 448 with I greater-than-or-equal-to 3 sigma(I) were used in the least-square refinement of the model to R = 0.034 (Rw = 0.044). T he structure of K6CrNb15O42 may be described as consisting of comer-sh ared and edge-shared octahedra the ring units composed of six octahedr a share comers along the c-axis to form a kind of hexagonal column oct ahedra chain, which is the first one discovered in niobates.