I am working on Mn-doped CH3NH3PbBr3 perovskite. I measured these samples by films. At the smallest amount of Mn doping, the lattice parameter increase initially. I am very confused here, the radius of Mn is smaller than Pb, shouldn't the lattice parameter become smaller here?
You are saying that, lattice parameters initially increase, then decrease and then again increase for gradually higher doping percentage of Mn. This is not anticipated ideally.
I think, it means, for some samples, substitutional doping has not occurred fully. Else, some interstitial doping has taken place. Besides, synthetic conditions might have varied a bit. The experiments should be repeated with sophisticatedly maintained synthetic conditions.
I think the increase or decrease in lattice parameters should be ideally consistent with the increase in doping concentration. I suggest you to repeat the synthesis procedure again Zhou Qian
Dear Zhou Qian ,
welcome!
Would you please us how did you measure the lattice consatnt and how much is the doping concentration.
May be more important is the resulting electronic and opto -electronic properties of the material?
The increase may be due to less binding energy with Mn leading to larger bond length.
Best wishes
Dear Zhou Qian,
the same trend was observed in the published article Article Structural, optical and dielectric properties of low tempera...
as doping with the smaller ions at the Pb2+ site in MAPbBr3 matrix leads to reduction in the distortion of the M-Br-M (M = Pb, Cd, Mn) bond angle, relaxation of the lattice strain to maintain the cubic perovskite structure, and resultant expansion of the MBr6 octahedral cage. We suggest that the expansion in the lattice parameter for low doping concentration may arise due to a similar response of the system. The expansion of the lattice parameter is not monotonic but exhibits a maximum at 5% and subsequently contracts. At higher doping concentration, the smaller size of the ion would overcome the initial expansion, leading to contraction of the Cd–Br octahedral cage
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