Abstract
The structure of a new calcium intergrowth tungsten bronze, CaxWO3, prepared at P = 80 kbar and T = 1670 K, has been studied by high-resolution transmission electron microscopy and supplementary techniques. The unit-cell dimensions, determined from X-ray powder data, are: a = 10.1500(9), b = 7.4232(7) and c = 3.7915(4) Å. The crystal structure is of (n)-ITB type with n = 2. It is isotypic with those recently reported for the RExWO3 bronzes (RE = Pr and Nd) prepared at P = 50 kbar. Combined electron diffraction and energy-dispersive X-ray spectroscopy (EDX) studies of thin crystallites showed that the hexagonal tunnels were less than half-filled with Ca atoms (x ≈ 0.07 ∓ 0.01). Electron diffraction patterns revealed ordered superstructures of (2)-ITB as well as an order—disorder transformation under the intense electron beam. A calcium bronze (Ca≈0.12WO3) with an hexagonal tungsten bronze structure (HTB) was also observed in the sample.
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