The decomposition of metal (Ti, Zr, Sn) alkoxides at 250 °C in a solution of tetradecene and dodecylamine resulted in the formation of ultra-small (1–2 nm) oxide nanoparticles. The nanoparticles showed unusual structural properties. The high-pressure orthorhombic phase was found for SnO2. The as-synthesized ZrO2 nanoparticles were only partially crystallized. It was possible to observe their in situ crystallization under the TEM beam. The TiO2 nanoparticles appeared amorphous, with only a few nanocrystals dispersed in the sample. The temperature evolution of the samples was investigated in situ by Raman spectroscopy. All SnO2 was converted to stable cassiterite at 350 °C. TiO2 and ZrO2 samples displayed phase stability reversal over a broad range of temperatures.