The tetragonal–monoclinic, ferroelastic transformation in yttrium tantalate and effect of zirconia alloying

Abstract

Oxide compositions of equimolar YO1.5 and TaO2.5 in the Y-Ta-Zr-O system have attractive properties for high temperature applications including as thermal barrier coatings. The effect of zirconia concentration, from 0 to 20 mole percent cation, on the tetragonal to monoclinic phase transition has been studied using high temperature X-ray diffraction, Raman spectroscopy, and electron microscopy. The transformation is reversible and the temperature variation of an order parameter based on the spontaneous strain is consistent with the transformation being ferroelastic, a critical feature for toughening at high temperatures. The presence of twin domains further supports this conclusion. Additionally, stabilization of the tetragonal phase with increasing ZrO2 is evident from the amount of partially retained tetragonal phase at room temperature.2

First-principles calculations of the high-temperature phase transformation in yttrium tantalate

“…However, as seen in 21 . This is also consistent with our finding that the temperature dependent order parameter can be represented in terms of the spontaneous breaking strains 42 .…”

“…This analysis is supported by recent TEM observations of twin boundaries with rotational relation of 95.05º between the domains 42 .…”

“…with the recent in-situ measurement of the transition temperature by high temperature powder Xray diffraction (1426 ± 7℃) 42 . The crystal structures and atomic positions of the two YTaO 4 polymorphs were also obtained at different temperatures using the same method.…”

Theoretical and experimental investigations of mechanical properties for polymorphous YTaO4ceramics

“…The YTaO 4 –ZrO 2 pseudo‐binary phase diagram from room temperature to 1600°C shows, over the entire compositional range, there are three regimes including YTaO 4 solid solution, ZrO 2 solid solution, and two‐phase region . In the YTaO 4 solid‐solution region, the incorporation of zirconia can effectively decline the Curie phase transition temperature of YTaO 4 between M and T phases, almost from 1425°C to 450°C . In the ZrO 2 rich area, the high temperature tetragonal phase of ZrO 2 (above 1060°C) can be stabilized to room temperature through the substitution of Zr 4+ by equal Y 3+ and Ta 5+ ions .…”

Interactions of Ta2O5 with water vapor at elevated temperatures

“…Ta 2 O 5 has a number of attractive properties as an EBC which include a good match of coefficient of thermal expansion, no reactivity with the underlying silicon‐based ceramic, and good thermal stability. In addition, complex oxides with a Ta 2 O 5 component are candidate coating materials . Regardless, if the coating is composed entirely of Ta 2 O 5 or contains Ta 2 O 5 in a complex oxide, it is important to understand its reaction with molten salts and water vapor.…”