Diatom frustules were used as bio-templates to synthesize functional ceramics via solid-gas displacement reactions. Silica based frustules were exposed to TiF4 at 3300C to form TiOF2 which is later converted to TiO2 (anatase) by heat treatment in air at 6000C. The TiO2 frustules were then exposed to Ba(OH)2 at 1200C or Sr(OH)2 at 1600C to form BaTiO3 or SrTiO3 respectively. Chemical composition, structure, and morphology of the converted frustules were studied by XRD, TEM, SEM, EDS. In both cases near complete conversion was achieved while retaining the morphology of the original silica frustules. Conversion of diatom frustules to Nb2O5 by solid-gas displacement reaction was also studied. Silica based frustules were exposed to NbF5 vapors at 3300C which formed niobium oxy-fluoride ( NbO2F) intermediate. Oxygenation of the intermediate was attempted in oxygen atmosphere at high temperatures which resulted in formation of Nb3O7F along with various off-stoichiometric niobium oxides. Conversion to Nb2O5 and its derivatives accompanied by evolution of NbOF3 which compromised the shape of the original frustules.