I have doped ZnO with yttrium by gel combustion method using citric acid as a fuel in the XRD data I am not getting any impurity peak of Y2O3 for 1% doping of Y but still the lattice parametters are decreased reative to pure ZnO, please explain if anyone has an idea about it.
In fact, this phenomenon is observed when any rare earth (RE) oxide is added as a dopant. Some of the BO of Zn are repaced as NBO by dopant RE oxide which occupy the interstitial sites (pores/ empty spaces/holes) and brings about nonlinearity in ZnO.So Y2O3 doping INCREASES NONLINEAR COEFFICIENT, REDUCES POROCITY ,lowers sintering temperature, decreases grain size of ZnO due to PINNING EFFECT of SPIENAL SPACE containing Y2O3..Also, Y (+3) and Zn (+2) differ in size/mass.All these changes brought about by even less than 1% addition of Y2O3 can change the lattice parameters (distance between unit cells in a crystal lattice) of ZnO. It has Wurtzite structure with hexagonal unit cell.
The increase in nonlinearity leading to the decrease in both the grain size and porocity are primarily responsible for the decrease in lattic constants.
Also if you are comparing the lattice constants of undoped and doped ZnO nanoparticles you have to make sure that the average crystallite size of both undoped and doped nanopartciles are nearly same. As lattice constants for some of the samples strongly depends on the average crystallite size upto certain extent.
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