The CaCuP films deposited by reactive sputtering at 490 °C are polycrystalline. In Figure we show the XRD pattern of five films around the stoichiometric point to illustrate the main trends in their structural properties as a function of the composition. In each film, the diffraction peaks above the noise level can be attributed to CaCuP in the P6 3 /mmc structure. Changes in the Cu/Ca ratio do not have a strong influence on the XRD pattern. On the other hand, substantially different patterns are obtained at different P contents (moving vertically in the ternary diagram in the inset of Figure ). When the P content is more than ∼ 2% above the ideal stoichiometry (Films D and E) the peaks become broader and less intense, indicating a smaller crystallite size and a higher fraction of non-crystalline material in the film, respectively. Furthermore, the (002) and (004) peaks become less intense for increasing P content, compared to the other peaks in the pattern. This indicates a tendency for the c-axis to align closer to the growth direction under P-poor conditions. The grain size of Film C in the substrate plane is on the order of 50 nm as estimated by SEM images (Figure ). †