Investigation on microstructures and thermo-physical properties of ferroelastic (Y1-xDyx)TaO4 ceramics

A series of ceramics of (Y 1-x Dy x )TaO 4 monoclinic phases (space group: I2 (5)) are prepared by the solid-state reaction method. The high-resolution transmission electron microscopy (HRTEM) suggest the (Y 1-x Dy x )TaO 4 ceramics possess ferroelastic domain, which is derived from reversible second-order ferroelastic transformation between the high-temperature tetragonal (t) and low-temperature monoclinic (m) phase. Similar to metastable tetragonal YSZ ceramics, the ferroelastic toughening mechanism may exist in m-phase (Y 1-x Dy x )TaO 4 ceramics through the shift or reorientation of ferroelastic domain under the stress field of a crack. The energy dispersive spectroscopy reveals that the elements of Y and Dy are inhomogeneous in the grain of (Y 1-x Dy x )TaO 4 ceramics, which breaks down the relationship of concave parabola between thermal conductivity and composition parameter (x). Moreover, the thermal conductivities (1.7–2.0 W/m/k at 900 ̊C) and thermal expansion coefficients (TECs) (10–11 × 10 −6 K −1 ) of (Y 1-x Dy x )TaO 4 ceramics are comparable to that of YSZ (yttria-stabilized zirconia). In view of the low thermal conductivity, high thermal expansion coefficients, good high-temperature phase stability and ferroelastic transformation, the (Y 1-x Dy x )TaO 4 ceramics show great potentials in the application of high-temperature thermal insulator materials, particularly as thermal barrier coatings .