Thermodynamic properties of the La ₂ O ₃ –ZrO ₂ system by Knudsen effusion mass spectrometry at high temperature

Rationale Zirconia doped with a lanthanum oxide system is of high interest due to its exceptional thermal stability for the development of high‐performance ceramics. It possesses the beneficial properties of pure zirconia, such as heat resistance, mechanical strength and inertness, but also eliminates its main disadvantage, i.e. brittleness. At high temperatures, components of such systems may vaporize selectively, leading to significant change in composition, and hence, the thermal resistance, phase stability and performance of the ceramic materials. Therefore, information on the vaporization processes and thermodynamic properties of the La 2 O 3 −ZrO 2 system is of great importance . Methods Knudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La 2 O 3 −ZrO 2 system at 2110 K. Pure La 2 O 3 was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis. Results Zirconia‐doped lanthania precursor powders and ceramics with La 2 O 3 of 33.3, 50, 70 and 90 mol.% content were manufactured by solid‐state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO 2 were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La 2 O 3 were calculated. Via XRD analysis it was shown that the phase composition of xLa 2 O 3 –(100–x)ZrO 2 powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen. Conclusions According to the XRD results combined with Rietveld refinement of the patterns, 33.3 La 2 O 3 –66.7 ZrO 2 ceramics after solid‐state synthesis are composed of well‐formed cubic pyrochlore‐type La 2 Zr 2 O 7 with 5 wt.% admixture of monoclinic and cubic ZrO 2 whereas 33.3 La 2 O 3 –66.7 ZrO 2 precursor powders after cryochemical synthesis correspond to low‐crystalline La(OH) 3 . The components of the La 2 O 3 –ZrO 2 system evaporate separately: there is no temperature range where lanthanum and zirconium gaseous species are present together. It was found that the activities of lanthania have low negative deviation from the ideal case.