NEUTRON-DIFFRACTION AND H-1 RIGID LATTICE WIDE-LINE NMR-STUDIES OF POWDER (K, BIIII, BIV) PYROCHLORES

The structure of an A cation-deficient pyrochlore (K, Bi)// approximately equals //1//. //5Bi//2O// minus //6(H//2O)// minus //1 has been investigated by powder neutron diffraction using a deuterated sample. Main results of previous X-ray work are confirmed: 25% of A sites are empty; only a small amount of oxygen is found in 8(b) positions, a greater proportion being located in 32(e) positions which are displaced toward the A vacancy. The latter oxygen atoms belongs to a heavy water molecule, the deuterium atoms of which are distributed near 96(g) positions. Proton wide-line nuclear magnetic resonance experiments were performed at 4 K using an undeuterated sample.