Thermal properties of Y1-xMgxTaO4-x/2ceramics via anion sublattice adjustment

A systematic investigation concerned with Y1-xMgxTaO4-x/2(x = 0, 0.08, 0.12, 0.16 and 0.20, respectively) ceramics was fabricated by a solid-state reaction method and characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and thermal analysis. XRD spectra display that all of the samples are excellently consistent with the standard XRD spectrum of monoclinic YTaO4(PDF No. 24-1415; space group:I2 (5)). The Raman peaks of the samples doped with Mg(2+)just widen slightly compared with those of pure YTaO4, which are in agreement with the results of XRD. The thermal conductivity of dense 7 wt%-8 wt% yttria-stabilized zirconia (7-8 YSZ) ceramic is about 2.5 W center dot m(-1)center dot K(-1)at 900 degrees C, while the Y1-xMgxTaO4-x/2(x= 0, 0.08, 0.12, 0.16 and 0.20) ceramics possess lower thermal conductivity in the range of 1.45-1.57 W center dot m(-1)center dot K(-1)at 900 degrees C, which declines by 35% compared with that of 7-8 YSZ. The lower thermal conductivities of Y1-xMgxTaO4-x/2(x= 0, 0.08, 0.12, 0.16 and 0.20) ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg(2+)ions defect complex. However, the thermal expansion coefficients are about 9.0 x 10(-6)-9.5 x 10(-6)K(-1)along with the different amounts of Mg(2+)doping at 1200 degrees C. Compared to the pure sample, the thermal expansion coefficient decreases slightly when the Mg(2+)doping amount is over 20%. The systematic investigations on the phase, microstructure, elastic and thermal properties of Y1-xMgxTaO4-x/2(x= 0, 0.08, 0.12, 0.16 and 0.20) ceramics will provide guidance for its application at high temperature, especially as thermal barrier coatings.