What do you mean by ‘correct result’? Your micrograph shows a fused set of aggregates made up of smaller primary sized particles. Only one (larger) particle is present. You could look at SSA with BET.
V R Arun Prakash Everything seen under TEM is an artifact of sample preparation and ‘particle’ selection. See attached for cubes. From A Primer of Higher Space Claude Bragdon The Manas Press, Rochester, New York (1913). You'll get a distribution of sizes for a completely monodispersed system (every particle the same).