A method for preparing highly dense functional oxides with crystallite size in the range of 10-20 nm. Using a high pressure modification of a the Spark Plasma Sintering (SPS) technique, rapid thermal cycles (<10 min) coupled with very rapid pressure increase up to 1 GPa can be obtained allowing high degree of compaction and very limited grain growth. This combination of techniques was employed to produce the finest-grained ceramics ever prepared in bulk form in the case of fully stabilized zirconia and Sm-doped Ceria.