Structure Determination of the α = 3, β = 6 Term of the (A3B2O6)α(A3B3O9)β Homologous Series (A = Ba, B = Rh) by a Combination of Powder X-ray Diffraction and Electron Microscopy

The α = 3, β = 6 term of the series (A3B2O6)α (A3B3O9)β has been synthesized in polycrystalline form. The structural characterization by powder X-ray diffraction, electron diffraction and high-resolution electron microscopy indicates that this material is isostructural with Ba9Co8O24. In the structure, seven face-sharing octahedra alternate with a trigonal prism defining chains running parallel to the c axis of a rhombohedral unit cell (Rc), with parameters a = 1.00766(4) nm and c = 4.1571(2) nm. The structural refinement shows the presence of a small percentage of Rh vacancies leading to the composition Ba9Rh7.92O24. Pauli paramagnetic behaviour is observed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)