Phase transitions and metastable phase diagram of nanocrystalline ZrO2-Sc2O3 solid solutions

P.M. ABDALA; D.G. LAMAS; A.F. CRAIEVICH; M.C.A. FANTINI

2007 Activity Report of the Brazilian Synchrotron Light Laboratory

Laboratorio Nacional de Luz Sincrotrón (LNLS)

Año: 2008 p. 1141 - 1141

1518-0204

ZrO2-Sc2O3 ceramics are intensively investigated because they exhibit the highest ionic conductivity among ZrO2-based systems. The physical properties of these materials are closely related to their crystal structures and phase changes. The polymorphs observed in this system have monoclinic, tetragonal, cubic or rhombohedral symmetries. The tetragonal phase can exhibit three forms: t, t’ and t". The stable tetragonal form is called the t form. The t’ and t" forms are metastable and have been observed in compositionally homogeneous materials. The further has similar crystal structure than the t form, but it is unstable in comparison with the mixture of the t-form and cubic phase, while the later has an axial ratio, c/a, of unity with the oxygen atoms displaced along the c axis from their sites of the cubic phase. However, the retention of the t"-form has not been reported in ZrO2-Sc2O3 solid solutions with large grain sizes, instead a mixture of cubic and rhombohedral b-phase has been observed. In this work, we investigated the crystal structure of ZrO2-Sc2O3 nanopowders with crystallite size of about 25 nm and their phase transitions at high temperature by synchrotron X-ray powder diffraction (SXPD). From these results, we proposed a metastable phase diagram for these materials.-Sc2O3 ceramics are intensively investigated because they exhibit the highest ionic conductivity among ZrO2-based systems. The physical properties of these materials are closely related to their crystal structures and phase changes. The polymorphs observed in this system have monoclinic, tetragonal, cubic or rhombohedral symmetries. The tetragonal phase can exhibit three forms: t, t’ and t". The stable tetragonal form is called the t form. The t’ and t" forms are metastable and have been observed in compositionally homogeneous materials. The further has similar crystal structure than the t form, but it is unstable in comparison with the mixture of the t-form and cubic phase, while the later has an axial ratio, c/a, of unity with the oxygen atoms displaced along the c axis from their sites of the cubic phase. However, the retention of the t"-form has not been reported in ZrO2-Sc2O3 solid solutions with large grain sizes, instead a mixture of cubic and rhombohedral b-phase has been observed. In this work, we investigated the crystal structure of ZrO2-Sc2O3 nanopowders with crystallite size of about 25 nm and their phase transitions at high temperature by synchrotron X-ray powder diffraction (SXPD). From these results, we proposed a metastable phase diagram for these materials.-Sc2O3 nanopowders with crystallite size of about 25 nm and their phase transitions at high temperature by synchrotron X-ray powder diffraction (SXPD). From these results, we proposed a metastable phase diagram for these materials.