Structural studies of calcium tungsten bronzes, CaxWO3, formed at high pressure

The structure of a new calcium intergrowth tungsten bronze, CaxWO3, prepare d at P = 80 kbar and T = 1670 K, has been studied by high-resolution transm ission electron microscopy and supplementary techniques. The unit-cell dime nsions, determined from X-ray powder data, are: a = 10.1500(9), b = 7.4232( 7) and c = 3.7915(4) Angstrom. The crystal structure is of (n)-ITB type wit h n = 2. It is isotypic with those recently reported for the RE WO bronzes (RE = Pr and Nd) prepared at P = 50 kbar. Combined electron diffraction and energy-dispersive X-ray spectroscopy (EDX) studies of thin crystallites sh owed that the hexagonal tunnels were less than half-filled with Ca atoms (x = 0.07+/-0.01). Electron diffraction patterns revealed ordered superstruct ures of (2)-ITB as well as an order-disorder transformation under the inten se electron beam. A calcium bronze (Ca approximate to(0.12)WO(3)) with an h exagonal tungsten bronze structure (HTB) was also observed in the sample.