Increase in d-spacing is attributed to difference in the ionic radii of Zn, Mn and Ag ions.The ionic radii of Mn, Ag ions are greater than the Zn ions (Mn : 80pm , Ag:94pm and Zn:74 pm). Thus it implies that 2theta shifts to lower values (Braggs law) and lattice volume increases and suggests that Mn and Ag ions are being incorporated into the lattice.

Increase in d-spacing is attributed to difference in the ionic radii of Zn, Mn and Ag ions.The ionic radii of Mn, Ag ions are greater than the Zn ions (Mn : 80pm , Ag:94pm and Zn:74 pm). Thus it implies that 2theta shifts to lower values (Braggs law) and lattice volume increases and suggests that Mn and Ag ions are being incorporated into the lattice.

Doped materials of Ag and Mn are arranged as a interstitial atoms inside the ZnO lattices, it is reason for the variations of the lattice planes.

It depends on the change of the location of dopant ion and the lattice parameters are influenced by the difference in ionic raddi of the involved elements.

Ionic radius of Zn2+ ions determine the lattice spacing value of ZnO semiconductor matrix. During impurity adding, the Zn2+ ions replaced by dopant ions. Therefore, with respect to ionic radius of doping element, the lattice parameter value is slightly shrinking (or) expanding. In your case, Both dopant ions (Mn, Ag) have higher ionic radius than that of Zn2+ ions. This is the reason for slightly increasing d-spacing value after doping.

What puzzles me is the huge value of lattice parameter change. Between 0.23 and 0.28 you observe practically a lattice parameter change of more than 20%. How reliable is this?

How much your material is doped? Or does this already describe another phase? A dotation of only some percent won't cause such big changes in lattice parameters. Moreover, with increasing dotation your images should become more blurred since the periodicity is no more exactly fullfilled as required for an ideal crystal (cf. martensite).

The position of the peaks shift toward lower or higher diffraction angles ‎with an increase of the Mn or Ag content, indicating changes in the lattice ‎parameters thus d-space due to the presence of tensile strain in the host upon ‎incorporation of the dopant ions into the basic cell in the grown films. The ‎change in lattice parameters is probably because the ionic radius of Mn2+ ‎‎(0.8 ˚ A) is larger than that of Zn2+ (0.74 ˚ A) ions, which indicates that the ‎divalent Mn2+ ions substituted for the Zn2+ ions in the ZnO crystal matrix.‎

I want to clear that and deviation from Hume – Rothery Rules causes change ‎in lattice parameters ‎thus interplaner space (d-space)

Hume – Rothery Rules

1. r (atomic radius) < 15%

2. Proximity in periodic table

i.e., similar electronegativities. If the difference in electronegativity is too great will tend to form intermetallic compounds instead of solid solutions

3. Same crystal structure for pure metals

4. Similar Valency

Metals have a greater tendency to dissolve metals of higher valency than lower valency

I agree with Dr Essam's reply. The shifting of XRD peaks are due to : 1. The microstrain (tensile or compressive) causes the shifting of X-ray diffraction peaks as compared to virgin sample because of substitution of foreign particles.  2. Stacking Faults sometimes cause shifting of peak position and variation of intensity. 3. Mounting of sample is not uniform ( say the virgin ZnO film of thickness x1 is  mounted on a TiO2 substrate, during modification -adding Mn or Ag via a physical / heating technique may decrease or increase the thickness of the filn x2 may cause the shifting of peak position, in order of micron or less). 4. New phases formed due to modification are also responsible for the shifting of peak position and d-value.

In the grown crystal the d- value is fingerprints of specific sample which is determined by XRD. The shifting of plane spacing (d-value) is due to  rearrangement of lattice  positions. It is due to doping of ions, atoms and impurity. The driving forces are electrostatic forces which rearrange the different atomic position inside the crystals. Another thing which affects the d value is stress forces which is external forces.

Due to higher ionic radius of Mn and Ag than Zn2+, d-spacing increases with respect to dopant concentration