Crystallization in hafnia- and zirconia-based systems

Crystallization of hafnia and zirconia and their alloys with silica and lanthana was studied in bulk and thin film samples by thermal analysis, X-ray diffraction and electron microscopy. Crystallization temperatures of hafnia and zirconia increase by more than 300 degreesC with increase of surface/interface area of the amorphous phase. Crystallization temperatures of zirconia and hafnia alloys with silica and lanthana increase with dopant content and exceed 900 degreesC for 50 mol% SiO2 and LaO1.5. Energies for tetragonal HfO2 and ZrO2 interfaces with amorphous silica were derived from their crystallization enthalpies from silicates as 0.25 +/- 0.08 and 0.13 +/- 0.07 J/m(2), respectively. The crystallization pathways in bulk powders and films of zirconia and hafnia can be interpreted as resulting from thermodynamic stabilization by the surface energy term of tetragonal and amorphous phases over monoclinic. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.