Effect of grain size and grain boundary defects on electrical and magnetic properties of Cr doped ZnO nanoparticles

•Single phase nanoparticles of pure ZnO and Cr doped ZnO have been synthesized through sol–gel route.•Defects like HO, H, and oxygen vacancy have been estimated via FTIR and XPS.•Dielectric and impedance spectroscopy have been discussed on the light of grain size and grain boundary defects.•There surface defects and size of nanoparticles effect on the FM properties of the samples.•The appearances of FM in pure ZnO indicate to the importance of grain sizes and grain boundary defect magnetic properties.

Nanostructure of Zn1−xCrxO (x = 0.0, 0.05 and 0.1) were synthesized successfully through sol–gel route. The effects of grain size and grain boundary defects on the electrical and magnetic properties have been investigated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results reveal the single-phase character. Crystallite sizes were obtained from the XRD patterns whose values are decreasing from ∼27 to ∼16 nm with increase in Cr content from 0% to 10% respectively. X-ray photoelectron spectroscopy (XPS) confirms the incorporation of Cr3+/Cr2+ ions in the lattice structure of ZnO, which causes decreasing in the valence electron density of Zn. Dielectric constant (ε) has been explained in the light of Maxwell–Wagner interfacial model, which differentiates between the structure of grain-core and grain-boundary. Complex impedance spectroscopy has been used to separate the grain and grain boundary contributions, the high resistivity values (107 Ω) can be attributed to the dominance of grain boundary resistance. The samples exhibit room temperature ferromagnetic (RT-FM) behavior, which has been discussed based on BMP model and effect of grain/grain boundary structure.