Thermal properties of Y1-xMgxTaO4-x/2 ceramics 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 Mg2+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·m-1·K-1at 900°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·m-1·K-1at 900°C,which declines by35%compared with that of 7–8 YSZ.The lower thermal conductivities of Y1-xMgxTaO4-x/2(x=0,0.08,0.12,0.16and 0.20)ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg2+ions defect complex.However,the thermal expansion coefficients are about 9.0910-6–9.5910-6K-1along with the different amounts of Mg2+doping at 1200°C.Compared to the pure sample,the thermal expansion coefficient decreases slightly when the Mg2+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.