K7-X-YBAYNB14P9O60(X=0.27(5), Y=0.63(3)), A NIOBIUM PHOSPHATE BRONZE - SYNTHESIS, STRUCTURE, AND PHYSICAL-PROPERTIES

Large dark blue plate-like single crystals of K7-x-yBayNb14P9O60 (x = 0.27(5), y = 0.63(3)) have been synthesized by a solid state technique . A single crystal X-ray diffraction study shows that it crystallizes in the orthorhombic space group Pmma(#51) with the lattice parameters a = 36.809(3), b = 10.596(1), and c = 6.459(1) Angstrom and z = 2. A f ull matrix least-squares refinement based on 2451 reflections for I > 2 sigma(I) yielded R(F) = 0.047 and R(w)(F-2) = 0.114. The title compo und is isostructural with the previously reported K7Nb14+xP9-xO60 (x = 0.13). Among the five unique K atoms in the crystal structure of K7Nb 14.13P8.87O60, only K(5) appears to be predominantly substituted by ba rium. K6.10B0.63Nb14P9O60 shows semiconducting behavior with an activa tion energy of 0.16(1) eV. Magnetic susceptibility measurements on a c ollection of randomly oriented single crystals indicated Curie behavio r with an effective magnetic moment of mu(eff) = 1.30 mu(B)/Nb4+. A co mparison of the structure as well as the electrical transport and magn etic properties of K6.10Ba0.63Nb14P9O60 With that of K7Nb14.13P8.87O60 is presented. (C) 1996 Academic Press, Inc.