Phase Equilibrium and Martensitic Transformation in Lanthana‐Doped Zirconia

Abstract

The system Zr02-La203 has been studied in the 0 to 15 mol% La203 range using X-ray diffraction and thermal analysis. Tho kinds of diagrams were elaborated: First is a phase equilibrium diagram where the eutectoid decomposition of ZrOz,,,(T) -+ Zr02,..(M) + Py,, occurs at 1100°C and 0.75 mol% La203 (Py is the pyrochlore compound ZrzLaz07). The maximum solubility of La203 in ZrOz,..(M) is 0.5 mol% at room temperature. Second, a nonequilibrium diagram is determined showing the correlations between grain size, La203 content, and the martensitic transformation temperature start (Ms).

Assessment of thermodynamic functions in the ZrO2–La2O3–Al2O3 system

“…The calculated data on invariant reactions are presented in Table 3. The calculations agree with experimental phase equilibria [21,[39][40][41]. The detailed comparison of the calculated phase diagrams with the experimental data is given elsewhere [42].…”

High‐Temperature Stable Zirconia Particles Doped with Yttrium, Lanthanum, and Gadolinium

“…These results are consistent with the www.particle-journal.com www.MaterialsViews.com fi ndings of Bastide et al for La-doped bulk zirconia, for which both a stabilization of the tetragonal phase with increasing La content and the formation of a pyrochlore phase after heating to 1200 °C were documented. [ 21 ] Furthermore, the appearance of the pyrochlore phase coincided with the observed increase in particle disintegration at high dopant concentrations. This fi nding can possibly be attributed to a mismatch in thermal expansion coeffi cient between La 2 Zr 2 O 7 (9.1-9.7 × 10 −6 K −1 ) and ZrO 2 /YSZ (10.3 × 10 −6 K −1 , 10.5-11.5 × 10 −6 K −1 ).…”

“…The diffraction refl exes for La 2 Zr 2 O 7 were no longer observed after reheating (see Supporting Information Figure S20), suggesting redissolution of the La 2 Zr 2 O 7 into the monoclinic phase. The La concentrations for the particles (3% and less) are borderline with the range for solid solubility in monoclinic zirconia, as given by the phase diagrams for the La 2 O 3 -ZrO 2 system, [22][23][24] but are higher than maximum solubility of 1% La reported by Bastide et al [ 21 ] Lastly, after heating at 1500 °C, all samples were fully sintered and had lost their spherical shape, as shown in the Supporting Information ( Figure S4). …”

“…[21][22][23][24] La 2 Zr 2 O 7 and Gd 2 Zr 2 O 7 have been considered for TBC applications due to their high melting points, phase stabilities, and low thermal conductivities. However, their use is impeded by a low toughness compared to YSZ [ 25 ] and a thermal expansion mismatch between the coating and metallic layer in the components.…”

LSM–YSZ Reactions in Different Atmospheres

“…This is due to the large solubility of Mn in YSZ (∼5 cat.-% in 8YSZ at 1,000°C in air and ∼8 cat.-% at 1,000°C and P(O 2 ) = 10 0 Pa) [16]. Due to small solubility of La and Sr in YSZ (<2 cat.% La and ∼0 cat.% Sr at temperature below 1,500°C) [17][18][19][20][21][22][23][24][25], the diffusion of La and Sr from LSM into YSZ and the corresponding influence on the interface stability is quite limited. It is however a different situation for the Mn diffusion, due to relatively high solubility of Mn in YSZ and its dependence on P(O 2 ).…”