Table 3: Comparison of particle size determined from TEM.

Methods
Particle size (TEM) (nm)
Crystal size (XRD) (nm)References

(i) Air oxidationNot mentioned26[23]
(ii) Ball milling50Not mentioned[24]
(iii) Combustion reaction20–3018–61[25]
(iv) Combustion route10–20 and 25–80 [26]
(v) Solid state reaction1015–30[27]
(vi) Autocombustion assisted7–87.4[28]
(vii) Sol-gel methodNot mentioned35[29]
(viii) Combustion reaction28–4628–46[30]
(ix) Microwave hydrothermal method23[31]
(x) Solution combustion synthesisFigure 651.9, 50.9, 34.4, 27.9, 24.4, 16.4Present works