Ref.: MceSi07-001

STRUCTURAL MODIFICATIONS INDUCED BY HYDROSTATIC PRESSURE ON LEAD METASILICATE PHASES

Apresentador: Ariano DeGiovanni Rodrigues

Autores (Instituição): Rodrigues, A.D.(Universidade Federal de São Carlos); Cunha, T.R.(Universidade Federal de Lavras); Pena, R.B.(Federal University of São Carlos (UFSCar)); Kaneko, U.F.(Centro Nacional de Pesquisa em Energia e Materiais); Pizani, P.S.(Universidade Federal de São Carlos);

Resumo:
Among the silicates, lead silicates stand out because of the possibility of making glass and glass ceramics with a wide range of compositions, which enables a great variety of applications ranging from domestic to high technology. For most of them, the control of the nucleation-growth-crystallization process is essential to determine the final physical properties of the resulting glass-ceramic. Nonetheless, the crystallization of silicates is not a straightforward process, but the system reaches intermediate metastable stages before reaching the most stable conformation. Due to the broad range of applications of the lead silicates and its high sensitivity to in situ structural analysis, the lead metasilicate PbSiO3 (PS) presents itself as a model system for the investigation of the structural evolution with pressure and temperature, allowing the evaluation of the thermodynamic quantities involved in this complex process, which are crucial to the physical description of the crystallization of the glasses presenting heterogeneous nucleation. Additionally, from the application point of view, the application of pressures capable of inducing changes in the energy of such phases can be viewed as a potential method to intervene in the stages of the overall crystallization, opening pathways to new properties for the resulting glass-ceramic. In this sense, we report on in situ high-pressure Raman and in-situ X-ray diffraction analyses of stable and metastable phases of PS, crystalized in a monoclinic and a hexagonal structure, respectively. The progressive redshift of the Raman peaks up to 5 GPa confirms that the structures are highly sensitive to the application of hydrostatic pressure. Abrupt shifts of peaks related to Pb-O and Si-O vibrations at P ~ 6GPa and P ~ 15GPa indicate the occurrence of significant structural rearrangements at these pressure values. By following the diffraction patterns we confirm the structural evolution induced by pressure, especially the abrupt shift of the main diffraction peaks for P ~ 6GPa and , which indicates a dramatic softening of the structure at this pressure regime.