Evolution of the local structure at Hf sites in SiHfOC upon ceramization of a hafnium-alkoxide-modified polysilsesquioxane: A perturbed angular correlation study

• Published in: Journal of the European Ceramic Society 2015-01, Vol.35 (1), p.29-35
• Main Authors: Umićević, Ana B., Cekić, Božidar Đ., Belošević-Čavor, Jelena N., Koteski, Vasil J., Papendorf, Benjamin, Riedel, Ralf, Ionescu, Emanuel
• Format: Article
• Language: English
• Subjects: HfO2/SiOC nanocomposites; Nanostructure evolution; Perturbed angular correlation (PAC); Polymer-derived ceramics (PDCs); Polymer-to-ceramic transformation
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2014.08.023

The evolution of the environment of Hf sites in a hafnium-alkoxide-modified polysilsesquioxane upon polymer-to-ceramic transformation was investigated via the perturbed angular correlation (PAC) method. The results of the PAC measurements on samples thermally treated at temperatures from 400 to 1300°C indicate that Hf is surrounded only by oxygen at all studied temperatures. This finding is in agreement with the evolution pathway of polymer-derived SiHfOC ceramics, which were reported to be generated as single-phase amorphous materials upon pyrolysis of alkoxide-modified polysiloxanes and subsequently to phase separate and crystallize towards HfO2/SiOC nanocomposites. Thus, the results presented here support our previous statement that there is a thermodynamic control on the phase separation and crystallization behavior of SiMOC (M=metal) ceramics (Ionescu et al. 96;2013:1899–1903), which in the case of Hf leads to the precipitation and crystallization of hafnia nanoparticles within a SiOC matrix.