Dear friend Loganathan Kulandaivel

The lower shifts in characteristic XRD (X-ray diffraction) peaks of metal-oxide/chalcogenide composites can be influenced by several underlying factors. Here are a few possible contributors:

1. Crystal Structure Modification: The introduction of chalcogenide materials into metal-oxide matrices can lead to changes in the crystal structure of the composite. These modifications may affect the lattice parameters, interatomic distances, and bond angles, resulting in peak shifts in the XRD pattern. Distortions in the crystal structure can arise due to the difference in ionic radii, electronegativity, and coordination environments between metal-oxide and chalcogenide components.

2. Chemical Interaction: Metal-oxide and chalcogenide materials can undergo chemical interactions within the composite. For instance, oxygen atoms from the metal-oxide component can form bonds with chalcogen atoms, leading to the formation of metal-chalcogenide bonds. These chemical interactions can induce changes in the local environment around the metal atoms, causing shifts in the XRD peaks.

3. Strain Effects: The incorporation of chalcogenide materials into metal-oxide matrices can introduce strain into the composite structure. This strain arises due to the differences in atomic sizes, thermal expansion coefficients, and crystal symmetries between the two components. The strain can influence the arrangement of atoms in the lattice, leading to peak shifts in the XRD pattern.

4. Composition and Stoichiometry: The relative amounts and stoichiometry of the metal-oxide and chalcogenide components can also affect the XRD peak shifts. Varying the composition or changing the metal-to-chalcogen ratio can lead to different local structures, which can manifest as peak shifts in the XRD pattern. Different compositions may result in the formation of different phases or the presence of impurities, which can contribute to peak shifts.

5. Size and Morphology: The size and morphology of the metal-oxide/chalcogenide composites can influence the XRD peak positions. Nanoscale materials or composite structures with high surface area-to-volume ratios can exhibit size-dependent lattice distortions or surface-related effects, which can cause shifts in the XRD peaks.

It is important to note that the specific factors contributing to lower shifts in XRD peaks can vary depending on the specific metal-oxide and chalcogenide materials, their synthesis methods, and the experimental conditions. The characterization of such composites requires a comprehensive analysis that considers various factors and their interplay.

Let us keep discussing and exploring this interesting topic at your convenience.

In addition to the excellent answer by Kaushik Shandilya you should also consider instrumental parameters as possible source of a peak shift in a diffraction pattern such as:

1) incorrect sample height (predominantly in Bragg-Brentano geometry). If the sample is positioned lower than the ideal position of the sample peaks will shift to lower angles on the detector. Can easily occur is the amount of sample is small.

2) 2Theta zero point offset, a common effect after replacing the X-ray tube, correction requires a careful well aligned measurement with a standard sample such as LaB6.