Low-temperature Structural Properties of Calcium Tungstate and Calcium Molybdate-II
- Details
- Category: Tungsten Information
- Published on Thursday, 16 July 2015 17:53
At room temperature CaWO4 and CaMoO4 echibit scheelite structure, having a complex layer structure with the layers being perpendicular to the c-axis. Each layer has a two-dimensional CsCl type arrangement of a Ca cation and complex anion WO4 –2 or MoO4 –2, which are surrounded by eight ions of opposite charge. Our studies reveal a scheelite type of structure in the whole temperature region investigated (5 – 300 K for CaWO4 and 12 – 300 K for CaMoO4). No structural anomalies have been observed.
The lattice parameters increase nonlinearly with temperature (see Figs. 1 and 2). There is a pronounced anisotropy of thermal expansion in CaWO4 and CaMoO4: the thermal expansion in the [100] direction is about 50 % of that in the [001] direction of the tetragonal cell. Thermal dependences of the lattice parameters obtained using synchrotron radiation agree well with the respective ones from elastic neutron scattering and links fairly well to the high-temperature data.
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