Improved thermal barrier materials exhibiting manufacturability, high toughness, and low thermal conductivity

Abstract

A modified ternary Zr-Ta-Y oxide system is provided that has a larger untransformed tetragonal phase that allows thermal barrier materials to be fabricated with improved properties of low thermal conductivity, higher sintering resistance, higher phase stability, and higher toughness.

Description

[Technical Field]

[0001] The present invention relates to improved thermal barrier materials, and more particularly to thermal barrier coatings that exhibit a non-transformable solid solution tetragonal phase that is stable over a wider composition range than previous thermal barrier materials. [Background technology]

[0002] The fuel efficiency of power generation and aerospace turbines increases as their operating temperatures rise. The drive to increase turbine efficiency exposes turbine components to increasingly higher temperatures, pushing the limits of the mechanical strength, corrosion, and erosion resistance of turbine component materials. One method used to mitigate the effects of elevated temperatures in turbines is to apply thermal barrier coatings (TBCs) to the hottest engine components to provide thermal insulation to the underlying metal or ceramic structural components. A typical TBC material known in the prior art is 6-8 wt. % yttria-stabilized zirconia, known as 7YSZ. 7YSZ has been the primary material used in TBCs due to its high coefficient of thermal expansion (CTE), which increases strain compliance; its relatively low thermal conductivity, which reduces the rate of heat transfer to cooled structural components; and its high toughness, which provides erosion and foreign object damage (FOD) protection. While most ZrO2-based ceramic materials have a relatively high CTE, providing a good coefficient of thermal expansion (CTE) match with Ni-based superalloys that may form the underlying structural components, the thermal conductivity and toughness of zirconia alloys can vary significantly depending on the alloying elements and compositions with which the ZrO2 is alloyed.

[0003] 7YSZ has high toughness compared to other compositions of yttria-stabilized zirconia, as first recognized and demonstrated in Stecura's reactor cycle data (S. Stecura, "Optimization of the NiCrAl-Y / ZrO2-Y2O3 Thermal Barrier System," NASA Technical Memorandum 86905, Cleveland, OH, 1985). The high toughness of 7YSZ was subsequently attributed to the ferroelastic toughening mechanism of YSZ (C. Mercer, J.R. Williams, D.R. Clarke, and A.G. Vans, "On a ferroelastic mechanism governing the toughness of metastable tetragonal-prime(t')Yttria-stabilized zirconia," Proceedings of the Royal Society A, vol. 463, no. 2081, 2007). Ferroelasticity increases a material's toughness when it can switch between equivalent crystallographic variants in its crystal structure upon mechanical loading. In the case of the tetragonal phase exhibited by 7YSZ, the tetragonal phase has three equivalent crystallographic variants that the material can reversibly switch between. These tetragonal variants correspond to three possible orientations of the c-axis in the tetragonal crystal structure, and the c-axis and the two a-axes of the material are not equivalent (i.e., a = a ≠ c). Therefore, mechanical damage to 7YSZ thermal barrier materials can be mitigated by reversible switching between such tetragonal variants, resulting in an erosion-resistant material and a FOD-damage-resistant material. Conversely, the cubic phase of materials such as 20YSZ lacks distinct crystallographic variants because the three principal axes of the crystal are equivalent (i.e., a = a = a). A tetragonal crystal structure is necessary for the activation of this ferroelastic toughening mechanism in ZrO2-based materials, and without such a structure, no other viable toughening mechanism exists in ZrO2-based thermal barrier materials. Therefore, a tetragonal crystal structure is required for ferroelastic-induced erosion resistance in thermal barrier materials.

[0004] ZrO2-based oxide materials are known to have relatively low thermal conductivity, but further reduction of such properties is desirable for effective operation of thermal barrier materials exposed to increasingly high operating temperatures. Efforts have been made to reduce the thermal conductivity of ZrO2-based materials. One known method for further reducing the thermal conductivity of a material system is by introducing mass disorder into the cation sublattice of a crystal structure already known to have relatively low thermal conductivity (M.R. Winter and D.R. Clarke, "Oxide Materials with Low Thermal Conductivity," Journal of the American Ceramic Society, vol. 90, no. 2, pp. 533-540, 2007). This can be achieved in ZrO2-based systems by increasing the concentration of stabilizer dopants in the ZrO2 alloy and / or by increasing the number of stabilizer dopant species in the alloy. For example, 20 wt% yttria-stabilized zirconia (20YSZ) and ZrO2 doped with three trivalent rare-earth ions, Y3+, Eu3+, and Yb3+ (tri-doped YSZ), both have lower thermal conductivities than 7YSZ. Therefore, it is possible to reduce the thermal conductivity of ZrO2 by increasing mass disorder on the cation sublattice through the use of large amounts of multiple stabilizer dopants alloyed into the material. The drawback of this approach to reducing thermal conductivity in thermal barrier materials is that both of these doping regimes (i.e., the use of large amounts of stabilizers and the introduction of multiple stabilizer ions of different sizes) tend to stabilize the cubic crystal structure of the ZrO2 system, as opposed to the tetragonal phase present in 7YSZ. The cubic crystal structure is disadvantageous because it does not exhibit sufficiently high toughness, as measured by the erosion resistance and FOD resistance of the material. As a result, this design approach creates a property trade-off in that the method for reducing thermal conductivity through increased doping concentration improperly transforms the material's crystal structure to a cubic crystal, which, for the reasons explained above, adversely affects the material's erosion and FOD resistance.

[0005] It is therefore desirable to provide a TBC that has both (i) a lower thermal conductivity than 7YSZ and (ii) the high toughness of 7YSZ provided by a ferroelastic toughening mechanism. To achieve both objectives, materials have been designed using multiple dopants that provide sufficient mass disorder on the cation sublattice while maintaining the material's average cation atomic size to favor tetragonal phase formation as opposed to cubic or other phases. One such multi-dopant material that has been shown to achieve this combination of materials is a solid-solution, non-transformable tetragonal phase (t) in the YO1.5-TaO2.5-ZrO2 system. (CAMacauley, ANFernandez and CGLevi, "Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1500 C," Journal of the European Ceramic Society, vol. 37, no. 15, pp. 4888-4901, 2017, and CA Macauley, ANFernandez, JSVan Sluytman and CGLevi, "Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1250 C,” Journal of the European Ceramics Society, vol. 38, pp. 44523-4532, 2018).

[0006] This solid solution utilizes a combination of large trivalent dopants and small pentavalent dopants to maintain an average cation atom size favoring the formation of a tetragonal phase, while also allowing for a total doping concentration that can exceed 7 atomic % with the combination of multiple dopants, thereby rendering the thermal conductivity of the solid solution substantially lower than that of 7YSZ. However, this solid solution phase is stable only over a relatively small compositional window, making it difficult to manufacture in both powder and coating form using conventional material manufacturing processes used to produce TBC materials and coatings. A related material was proposed in U.S. Pat. No. 11,479,846, which produced a similar composition. However, the material described in U.S. Pat. No. 11,479,846 has clear deficiencies. Specifically, instead of achieving a single-phase material with low thermal conductivity and high toughness, a combination of phases is produced. The use of multiphase materials has significant drawbacks. For example, it is possible to produce a second phase that is not tetragonal and does not exhibit the ferroelastic toughening mechanism that provides erosion resistance. Additionally, the presence of one or more other types of phases that do not have significant mass disorder on the cation lattice results in an insufficient reduction in thermal conductivity to provide thermal protection. Instead, the composite material performance result is a combination of the properties of desirable and undesirable phases for each aspect of the coating performance metric.

[0007] As a result, there is a continuing need for thermal barrier materials that exhibit high toughness and low thermal conductivity. Summary of the Invention

[0008] The present invention may include any of the following aspects in various combinations, and may also include any other aspects described below in the written description or accompanying drawings.

[0009] In a first aspect, there is provided a modified improved thermal barrier composition comprising a first oxide comprising zirconium oxide and cerium oxide, a second oxide comprising one or more second oxide cations of the elements tantalum, niobium, or combinations thereof, and a third oxide selected from the group consisting of oxides of the rare earth elements yttrium, scandium, and any combinations thereof.

[0010] In a second aspect, there is provided a modified thermal barrier material, the material having phase stability at high temperatures of at least 1500°C for at least 100 hours, low thermal conductivity of less than about 2 W / m / K, and a thermal conductivity of less than about 20 J / m 2 A modified thermal barrier material is provided, characterized as a substantially single phase of a non-transformable solid solution tetragonal phase, that exhibits equal to or greater toughness and resistance to sintering at temperatures of at least 1500°C that result in less microstructural degradation than commercially available 7 weight percent yttria-stabilized zirconia materials.

[0011] In a third aspect, there is provided a modified advanced thermal barrier composition comprising a first oxide comprising zirconium oxide, hafnium oxide, or a combination thereof, and cerium oxide; a second oxide comprising one or more second oxide cations of the elements tantalum, niobium, or a combination thereof; and a third oxide selected from the group consisting of oxides of the rare earth elements yttrium, scandium, and any combination thereof. [Brief explanation of the drawings]

[0012] The objects and advantages of the present invention will be better understood from the following detailed description of preferred embodiments thereof when taken in conjunction with the accompanying drawings in which like numerals refer to like features throughout. [Figure 1a] 1 shows a ternary phase diagram for the conventional Zr-Ta-Y oxide system, with values ​​given in atomic percentage (at%), with 10 at% increments on each of the three axes. [Figure 1b]1 shows a modified ternary phase diagram of FIG. 1a in accordance with the principles of the present invention, with values ​​given in at% and each of the three axes in 10 at% increments. [Figure 2] 1B shows an X-ray diffraction pattern of a powder material produced having the composition of the expanded field of FIG. 1B, in accordance with the principles of the present invention, which is indicative of a substantially single-phase tetragonal material. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention overcomes the aforementioned drawbacks. The present invention relates to compositions within a distinct modified phase 50 shown in FIG. 1b. The modified phase 50 is a single-phase, substantially non-transformable solid solution tetragonal phase. Compositions within such modified phase 50 result in materials that exhibit low thermal conductivity while maintaining high toughness, thereby overcoming the property tradeoffs faced by conventional materials.

[0014] The relationship and function of the various elements of the present invention will be better understood from the following detailed description. The detailed description contemplates various permutations and combinations of features, aspects, and embodiments as being within the scope of the present disclosure. Accordingly, the present disclosure may be specified to comprise, consist of, or consist essentially of any such combinations and permutations of these specific features, aspects, and embodiments, or selected one or more of them.

[0015] The term includes the specifically mentioned words, derivatives thereof, and words of similar import. The embodiments illustrated below are not intended to be exhaustive or to limit the invention to the precise form disclosed. The invention may include any of the following embodiments in various combinations, as well as any other aspects described below in the written description or accompanying drawings. These embodiments have been chosen and described to best explain the principles of the invention, its application and practical use, and to enable others skilled in the art to best utilize the invention.

[0016] Unless otherwise indicated, all percentages "%" used herein are in units of atomic percentage, denoted as "at%" or "atomic %" or "atomic percent."

[0017] As used herein and throughout, the term "conventional thermal barrier material" is intended to mean a thermal barrier of composition 7 wt. % yttria stabilized zirconia (7YSZ).

[0018] As used herein and throughout, the term "material" includes compositions of the present invention that can be manufactured in any material form (eg, powders and coatings).

[0019] As used herein and throughout, the term "phase stable" is intended to mean that the non-transformable solid solution tetragonal phase persists for at least 100 hours at elevated temperatures of at least 1500° C. As used herein and throughout, "solid solution" does not include multiphase materials.

[0020] As used herein and throughout, "single phase" means a structurally substantially uniform and distinct region of material having the signature shown in the present invention XRD of FIG.

[0021] As used herein and throughout, the term "rare earth element" is intended to mean the elements lanthanum, cesium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and ytterbium, and any combination thereof.

[0022] The present inventors have recognized that for a new generation of low thermal conductivity, high toughness thermal barrier coating (TBC) materials to be effective, they preferably exhibit each of the following characteristics: (1) they are phase stable in a substantially untransformed tetragonal phase at temperatures of at least 1500°C for greater than 100 hours; (2) they exhibit sintering resistance at temperatures of at least 1500°C that exhibits less microstructural degradation than commercially available 7 weight percent yttria-stabilized zirconia materials; (3) they provide the system with a low thermal conductivity (i.e., "low k") of less than about 2 W / m / K; and (4) they exhibit a thermal conductivity of less than about 20 J / m 2 and (5) they are manufacturable (e.g., have a phase window wide enough to allow for the fabrication of powders and coatings that maintain the desired non-transformable tetragonal phase throughout the manufacturing process). Currently, no thermal barrier system possesses all of these characteristics.

[0023] In addition to identifying the need for a single, untransformed solid solution tetragonal phase, the present invention recognizes the need to increase or broaden the compositional range over which the untransformed tetragonal phase exhibits stability, thereby producing an effective TBC possessing the above characteristics. 1.5 -TaO 2.5The system (C.A. Macauley, A.N. Fernandez, J.S. Van Sluytman and C.G. Levi, "Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1250°C," Journal of the European Ceramics Society, vol. 38, pp. 44523-4532, 2018) contains a stable, non-transformable tetragonal solid solution phase over a narrow compositional range with high tetragonality due to the combination of large cations (Y3+) and small cations (Ta5+) substituted en masse onto the zirconia lattice. Unfortunately, this material system presents significant processing and cost challenges. The inventors have determined that these drawbacks result from the use of a significant amount of tantalum oxide and a small chemical processing window that adversely affects manufacturability due to the stability of the non-transformable tetragonal phase over only a narrow compositional range, as shown in Figure 1a. Figure 1a shows the performance of conventional ZrO2-YO1.5 at 1500°C. 1.5 -TaO 2.5 The phase equilibrium in the system ZrO2-YO at 1500℃ is shown. 1.5 -TaO 2.5 The non-transformable solid solution tetragonal phase, calculated and experimentally confirmed for the system, is marked "t." This phase 10 marked "t" and the phase 30 marked "c" are both single phases on the phase diagram, representing the compositional windows of the single tetragonal and cubic phase material, respectively. The tetragonal phase 10 shares a phase boundary 20 with an additional multi-phase 40 marked "c+t." This phase 40 defines a compositional window where the material exhibits both the cubic and tetragonal phases unfavorably.

[0024] The present invention provides a novel approach to producing thermal barrier materials with a non-transformable tetragonal phase that exhibits stability over a sufficiently wide composition range. In particular, the present invention provides a method for converting cerium oxide into ZrO2-YO 1.5 -TaO 2.5 It is intended for incorporation into the ternary system as well as other functionally equivalent ternary systems described herein below. Cerium oxide is ZrO2-YO 1.5 -TaO 2.5When added to the system, a non-transformable tetragonal phase is created, significantly increasing the composition range that remains stable, as clearly shown in phase 50 in Figure 1b. Ce cations can substitute onto the zirconium lattice, resulting in Zr 4+ Because of the larger ion size compared to Zr 4+ This alleviates oxygen crowding around the ions, thereby maintaining the average cation size necessary to produce the tetragonal phase. The overall manufacturability of materials (e.g., powder compositions and coatings) made therefrom is significantly increased due to the increased compositional range over which the non-transformable tetragonal phase exhibits stability, as shown by a comparison of the "t" phase (i.e., the narrow phase boundary 10 in Figure 1a versus the expanded phase boundary 50 in Figure 1b). Specific manufacturability improvements enabled by the present invention include reduced sensitivity to the manufacturing process, increased toughness due to the presence of a single-phase ferroelastically active material, and reduced thermal conductivity due to increased mass disorder on the cation sublattice. It should be understood that, prior to the advent of the present invention, thermal conductivity and toughness were considered competing design parameters, and therefore achieving lower thermal conductivity came at the expense of toughness.

[0025] Referring to FIG. 1b, the estimated location of the modified phase boundary 60 for the untransformed tetragonal single phase 50 of the new solid solution is calculated using rule-of-mixture calculations of the average cation sizes of the constituent elements of the modified material as defined by the symmetry and valence state of those elements when alloyed into the ZrO2 tetragonal crystal structure. For the constituent elements alloyed into the tetragonal ZrO2 crystal structure, the cation size of tetravalent cerium is 0.97 Å, the cation size of tetravalent zirconium is 0.84 Å, the cation size of trivalent dopant yttrium is 1.019 Å, and the cation size of pentavalent dopant tantalum is 0.74 Å. The composition defining the modified phase boundary 60 is calculated to have an average cation size equal to that of 18 atomic percent ceria-stabilized zirconia. 18 at.% ceria and a corresponding average cation size of 0.8634 Å represent the highest composition of cerium that can be added to a ZrO2 binary system that exhibits a solid solution tetragonal phase. More than 18 at.% ceria may not render the composition single-phase. The calculations are repeated, selecting an at.% Ce less than 18 at.% to determine how much yttria and tantala must be present in the zirconia lattice to achieve the same or smaller average cation size of 0.8634 Å achieved in 18 at.% cerium-stabilized zirconia. In this way, a modified phase boundary 60 is achieved based on the average cation size rule of mixtures for 18 at.% CSZ.

[0026] ZrO2-YO 1.5 -TaO 2.5 Members of the system require intimate and vigorous mixing of lattice cations during processing to achieve significant phase stability, as represented by Figure 1a. However, this typically requires energy-intensive chemical processing routes, which can further introduce significant costs and environmental hazards to powder production. A given amount of cerium oxide is added to ZrO2-YO 1.5 -TaO 2.5By adding cerium oxide to the solid solution of the system and expanding the range of phase stability of its non-transforming tetragonal phase, more practical solid solution processing techniques can be used to produce resulting coating materials with significantly higher temperature phase stability of the non-transforming tetragonal phase. By incorporating cerium oxide to expand the compositional range over which the non-transforming tetragonal phase is stable, thermal barrier materials are produced that are less susceptible to phase decomposition even when exposed to high temperatures for extended periods of time. In this way, the materials of the present invention can provide manufacturable powder processing solutions that were not possible before the advent of the present invention. In addition to expanding the range of acceptable powder processing techniques to include less energy-intensive techniques, the use of cerium oxide as a co-dopant preferably reduces the amount of tantalum oxide required to achieve stabilization of the non-transforming tetragonal phase by altering the effective average ionic size of the cations on the lattice.

[0027] In another embodiment of the present invention, for example, Ta 5+ Similar performance results are observed for materials made for the same ternary system by using pentavalent niobium oxide as a small dopant instead of, or in addition to, the oxides. Additionally, trivalent rare earth oxides and yttrium and scandium oxides can both be used alone or in combination as large dopant ions, since these elements serve the same purpose in stabilizing the nontransformable tetragonal phase.

[0028] The compositions of the present invention are selectively formulated to consist of a first oxide comprising zirconium and / or hafnium oxide and cerium oxide, a second oxide comprising a second oxide cation of the elements tantalum and / or niobium, and a third oxide selected from the group consisting of the rare earth elements yttrium and scandium, or any combination thereof. Trace impurities of up to about 0.5 atomic percent may be present in the composition. As used herein and throughout, the term first oxide is intended to mean that it is present in the maximum amount. It should be understood that the second and third oxides may be utilized in any amount, so long as each is present in an amount less than the first oxide.

[0029] Without being bound by any theory, the inventors believe that the addition of cerium to the YO1.5-TaO2.5-ZrO2 system increases the size of the single-phase tetragonal solid solution phase by entering the system as a tetravalent dopant with an ionic size of approximately 0.97 Å, which is larger than the ionic size of tetravalent zirconium (0.84 Å) in the zirconium oxide crystal lattice, but smaller than the trivalent dopant yttrium (1.019 Å) and larger than the pentavalent dopant tantalum (0.74 Å). This intermediate-sized cerium dopant acts to stabilize the tetragonal phase without introducing oxygen vacancies, thereby resulting in a more stable tetragonal structure. Additionally, the trivalent dopant ytterbium, having a cation size of 0.985 Å, can substitute for yttrium in greater amounts while maintaining the average cation size below the upper limit of 0.8634 Å, thereby desirably increasing the size of the modified solid solution non-transformable tetragonal phase for the ternary system YbO1.5-TaO2.5-ZrO2.

[0030] Illustrative examples of compositions bounded by a preferred modified field are now described. The oxide composition is about 2 to about 20 atomic percent cerium oxide, about 1 to about 15 atomic percent tantalum oxide, and about 1 to about 15 atomic percent ytterbium oxide, with the balance being ZrO. More preferably, the exemplary composition window occurs when cerium oxide is about 5 to about 15 atomic percent, tantalum oxide is about 1 to about 7 atomic percent, ytterbium oxide is about 5 to about 10 atomic percent, and the balance is zirconium oxide. All chemicals having the aforementioned ranges fall within the modified field 50 of FIG. 1b and are therefore advantageously single-phase, untransformed tetragonal solid solution phases. [Example]

[0031] Illustrative Examples A powder having a composition within the modified phase field 50 ("t") in Figure 1b was prepared by typical solid solution processing techniques. An X-ray diffraction pattern of the powder material was obtained. The X-ray diffraction pattern is shown in Figure 2 and indicates a solid solution tetragonal single-phase material consistent with the present invention. The diamond locations in Figure 2 indicate the expected peaks for a solid solution tetragonal single-phase material. The alignment of the diffraction pattern peaks with the diamond locations confirms the presence of a solid solution tetragonal single-phase material. No peaks for other phases were observed in Figure 2. This testing verified the manufacturability of the material of the present invention. In contrast, most relevant cerium-free compositions prior to the present invention have been observed to be multiphase, as indicated by the multiphase field 40 in Figure 1a, and have been reported in the published literature. (CAMacauley, ANFernandez, JSVan Sluytman and CGLevi, "Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1250C," Journal of the European Ceramics Society, vol. 38, pp. 44523-4532, 2018).

[0032] The modified TBC composition of the present invention can be utilized as part of any suitable TBC system, including, by way of example, as part of a layer of yttria stabilized zirconia (YSZ) exhibiting a non-transforming tetragonal phase disposed between the bond coat and the modified TBC composition of the present invention. The layers of the TBC system include (i) a low thermal conductivity barrier coating of the present invention (which may be formed over the bond coat) having a composition that forms a non-transforming tetragonal phase, which provides more thermal protection at higher operating temperatures (e.g., 1350°C or higher), and (ii) a commercially available YSZ layer that acts as an additional layer to strengthen the bond by reducing stresses due to the coefficient of thermal expansion (CTE) mismatch between the layers. The TBC may comprise (iii) a continuous oxide layer (TGO) formed on a metallic bond coat; (iv) a metallic bond coat with additional chromium and / or aluminum for improved oxidation protection; and (v) a high-temperature material acting as a substrate for critical components. Other suitable examples are contemplated. Generally speaking, the TBC of the present invention can be incorporated with other layers to form an improved thermal barrier system, providing a so-called "tough phase" with lower thermal conductivity. The TBC material of the present invention can be applied in a microstructure that provides increased strain tolerance (providing longer life after repeated thermal cycling), resulting in improved thermal barrier performance while meeting design criteria (life after repeated thermal cycling). The resulting TBC system has substantially improved performance, allowing for increased thermal protection while maintaining a high thermal barrier. The present invention can enhance thermal barrier systems, enabling components operating in high-temperature environments to function at higher surface temperatures and exhibit longer life. The TBC material of the present invention can be disposed in a layer on an airfoil or turbine component at a thickness that can range from about 1 to about 1500 microns, more preferably from about 25 to about 1000 microns. The TBC material can be deposited by any suitable technique known in the art, including air plasma spray or electron beam evaporation. Preferably, the TBC material has a columnar structure when deposited by electron beam evaporation.

[0033] While we have shown and described what are considered to be certain particular embodiments of the invention, it will of course be understood that various modifications and changes in form or detail can be readily made therein without departing from the spirit and scope of the invention. It is therefore intended that the invention not be limited to the exact forms and details shown and described herein, nor be limited to anything less than the full scope of the invention disclosed herein and claimed below.

Claims

1. 1. A modified advanced thermal barrier composition comprising: a first oxide comprising zirconium oxide and cerium oxide; a second oxide comprising one or more second oxide cations of the elements tantalum, niobium, or a combination thereof; and a third oxide selected from the group consisting of the oxides of the rare earth elements yttrium, scandium, and any combination thereof.

2. 10. The modified thermal barrier composition of claim 1, wherein the composition forms a substantially single-phase, non-transformable solid solution tetragonal solid solution phase material.

3. 10. The modified thermal barrier composition of claim 1, wherein the second oxide cation is tantalum.

4. 10. The modified thermal barrier composition of claim 1, wherein the second oxide cation is niobium.

5. 10. The modified thermal barrier composition of claim 1, wherein the third oxide is an oxide of yttrium.

6. 10. The modified thermal barrier composition of claim 1, wherein the third oxide is an oxide of ytterbium.

7. The composition comprises, based on total atomic percent: about 2 to about 20 atomic percent CeO; about 1 to about 15 atomic percent of a second oxide; about 1 to about 15 atomic percent of a third oxide; trace impurities of about 0.5 atomic percent or less; 10. The modified thermal barrier composition of claim 1, comprising: ZrO2; and the balance ZrO2.

8. The composition comprises, based on total atomic percent: about 5 to about 15 atomic percent CeO; about 1 to about 7 atomic percent of said second oxide; about 5 to about 10 atomic percent of said third oxide; trace impurities of about 0.5 atomic percent or less; 10. The modified thermal barrier composition of claim 1, comprising: ZrO2; and the balance ZrO2.

9. 10. The modified thermal barrier composition of claim 1, wherein the first oxide is substantially zirconium oxide, the second oxide is substantially tantalum oxide, and the third oxide is substantially ytterbium oxide.

10. 10. The modified thermal barrier composition of claim 1, wherein the second oxide is tantalum oxide and the third oxide is ytterbium oxide.

11. 10. The modified thermal barrier composition of claim 1, wherein the composition forms a substantially single-phase tetragonal solid solution phase material.

12. 1. A modified thermal barrier material, the material having phase stability at high temperatures of at least 1500° C. for at least 100 hours, low thermal conductivity of less than about 2 W / m / K, and low thermal conductivity of less than about 20 J / m ２ A modified thermal barrier material characterized as a substantially single phase of untransformed tetragonal phase that exhibits equal to or greater toughness and resistance to sintering at temperatures of at least 1500°C that result in microstructural degradation that is less than that of commercially available 7 weight percent yttria-stabilized zirconia materials.

13. The modified thermal barrier material of claim 12, disposed in a layer on an airfoil, said layer having a thickness of from about 1 to about 1500 microns.

14. 13. The modified thermal barrier material of claim 12, disposed in a layer on a turbine component, said layer having a thickness of from about 25 to about 1000 microns, and wherein the thermal barrier coating is deposited by air plasma spraying.

15. The modified thermal barrier material of claim 12 , disposed in a layer on a turbine component, the microstructure of the layer being columnar, and the layer being deposited by electron beam physical vapor deposition.

16. The thermal barrier coating composition of claim 1 , wherein the bond coat is provided on a substrate comprising a turbine engine component.

17. 1. A modified advanced thermal barrier composition comprising: a first oxide comprising zirconium oxide, hafnium oxide, or a combination thereof, and cerium oxide; a second oxide comprising one or more second oxide cations of the elements tantalum, niobium, or a combination thereof; and a third oxide selected from the group consisting of the oxides of the rare earth elements yttrium, scandium, and any combination thereof.

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