In this study, flame aerosol synthesis of phosphor (Y2O3:Eu3+) and NMC (LiNi1/3Mn1/3Co1/3O2) particles was performed. The particle size distribution and morphology of the crystalline particles synthesized from aqueous metal nitrate solutions aerosolized by the new submicron droplet atomizer was compared with those of the particles obtained by means of regular ultrasonic nebulization. Product microscopic analysis demonstrated considerable differences in final particle size distribution as well as in particle morphology and in surface structure when submicron and micron-size droplets were utilized. A schematic diagram of particle formation routes from initial aerosol droplets was proposed and a theoretical model implementing combined timescale analysis and thermodynamic approach was developed. The model enables predicting final particle morphology from initial droplet diameter, concentration of solute, rate of surrounding gas temperature change and thermodynamic properties of solution. The results demonstrate that the developed theoretical approach fairly explains the experimental observations and can be helpful in forecasting droplet-to-particle formation routes and morphology for flame aerosol particle synthesis.