Hydrothermal Synthesis,Luminescence, and Phase Stability of Solid Solution Nanocrystals Based on Y3NbO7 and ZrO2

Cubic solid solution nanocrystals in the zirconia (ZrO₂)–yttrium niobate (Y₃NbO₇) system were directly formed at 180°C–240°C from the precursor solution mixtures of NbCl₅, ZrOCl₂, and YCl₃ under mild hydrothermal conditions in the presence of aqueous ammonia. The lattice parameter corresponding to cubic phase linearly changed according to the Vegard's law in the wide composition range of ZrO₂ (mol%) = 10–90 in the ZrO₂–1/4Y₃NbO₇ system. The progress of the formation of nanocrystalline solid solutions based on the Y₃NbO₇ was assisted via the presence of ZrO₂ component as a promoter with the same fluorite‐type structure. The optical band gap of the solid solutions was in the range 3.4–3.7 eV. Broadband emissions centered at 360–380 and 390 nm were observed for the nanocrystalline cubic solid solutions and pure cubic Y₃NbO₇, respectively, under excitation at 240 nm Xe lamp. The nanosized cubic crystallites of the solid solutions were maintained after heat treatment up to 800°C for 1 h air. The cubic phase of the solid solutions in the ZrO₂–1/4Y₃NbO₇ system was maintained after heat treatment at 1400°C in air.     

Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics.In this work, phase equilibria in ternary CeO₂–La₂O₃–Dy₂O₃ and binary La₂O₃–Dy₂O₃ systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO₂–La₂O₃–Dy₂O₃ system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO₂ with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln₂O₃.In the La₂O₃–Dy₂O₃ binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La₂O₃, monoclinic modification B-Dy₂O₃ and cubic modification C-Dy₂O₃ separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La₂O₃ are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy₂O₃ at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy₂O₃ in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy₂O₃.In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La₂O₃ in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.     

Oxygen‐ion conduction in scandia‐stabilized zirconia‐ceria solid electrolyte (xSc2O3–1CeO2–(99−x)ZrO2, 5 ≤ x ≤ 11)

Solid oxide fuel cells (SOFCs) operating at intermediate temperature (500°C‐700°C) provide advantages of better durability, lower cost, and wider target application market. In this work, we have studied Sc₂O₃ (5‐11 mol%) stabilized ZrO₂–CeO₂ as a potential solid electrolyte for application in IT‐SOFCs. Lower Sc₂O₃ doping range than the traditional 11 mol% Sc₂O₃‐stabilized ZrO₂ is an interesting research topic as it could potentially lead to an electrolyte with reduced oxygen vacancy ordering, lower cost, and higher mechanical strength. XRD and Raman spectroscopy was used to study the phase equilibrium in ZrO₂–CeO₂–Sc₂O₃ system and impedance spectroscopy was done to estimate the grain, grain boundary, and total ionic conductivities. Maximum for the grain and grain‐boundary conductivities as well as the tetragonal‐cubic phase boundary was found at 8‐9 Sc₂O₃ mol% in ZrO₂‐1 mol% CeO₂ system. It is suggested that the addition of 1 mol% CeO₂ in the ZrO₂ host lattice has improved the phase stability of high‐conductivity cubic and tetragonal phases at the expense of low‐conductivity t′‐ and β‐phases.     

Interaction of ceria and erbia in air within temperature range 1500–600 °C

Phase equilibriums and structure transformations in the CeO₂–Er₂O₃ system have been studied within 1500–600 °C in the full concentration range using XRD and petrography methods. It was established that the system is characterized by the formation of solid solutions on the basis of cubic modification of Er₂O₃ (C-type) and fluorite CeO₂ (F-type). Solubility limits and concentration dependences of lattice parameters were determined for the phases forming in the system.     

Temperature–stable dielectrics based on Cu–doped Bi2Mg2/3Nb4/3O7 pyrochlore ceramics for LTCC

Temperature–stable dielectrics based on Cu–doped Bi₂Mg_2/3Nb_4/3O₇ pyrochlore ceramics were prepared by conventional solid–state reaction. Microstructure analysis indicates that all of the specimen maintain the cubic pyrochlore phase, a fluorite–like phase of Bi₃NbO₇ and a Bi₅Nb₃O₁₅ formed for Cu doping. The dielectric constant is dominated by densification of samples and secondary phases, while the dielectric loss is related by the secondary phases, grain boundaries, and leakage current characteristics. The (1-x)BMN - xCuO(x = 0.1 mol%) ceramic sintered at 925 °C shows excellent dielectric properties with dielectric constant of ~184.06, dielectric loss of ~0.0017 and near zero τ_ε (?20 ppm/°C) is obtained at sintering temperature of 925 °C, which could be a promising candidate for LTCC.     

Phase relation studies in the CeO2–La2O3–Er2O3 system at 1500°C

Materials based on CeO₂–La₂O₃–Er₂O₃ system are promising candidates for a wide of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the isothermal section of the phase diagram for 1500 °C was investigated. The phase relations in the CeO₂–La₂O₃–Er₂O₃ ternary system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. To study phase relationships at 1500 °C the as-repared samples were thermally treated in two stages: at 1100 °C (for 300 in air) and then at 1500 °C (for 70 h in air) in the furnaces with heating elements based on Fecral (H23U5T) and Superkanthal (MoSi2), respectively. The solid solutions based on various polymorphous forms of constituent phases and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the CeO₂–La₂O₃–Er₂O₃ system has been constructed. It was established that in the ternary CeO₂–La₂O₃–Er₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, cubic modification of CeO₂ with fluorite-type structure (F), cubic modification Er₂O₃ and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions. The maximal solubility of ceria in LaErO₃ was found to be around ∼ 2 mol% CeO₂ along the section CeO₂–(50 mol % La₂O₃ –50 mol% Er₂O₃).     

Structural parameters and oxygen ion conductivity of Y2O3–ZrO2 and MgO–ZrO2 at high temperature

The oxygen ion conductivity of zirconia-based solid electrolytes doped with 8 mol% Y₂O₃–ZrO₂ (YSZ) and 9 mol% MgO–ZrO₂ (Mg-PSZ) at high temperature was investigated in terms of their thermal behavior and structural changes. At room temperature, YSZ showed a single phase with a fluorite cubic structure, whereas Mg-PSZ had a mixture of cubic, tetragonal and some monoclinic phases. YSZ exhibited higher ionic conductivity than Mg-PSZ at temperatures from 600 °C to 1250 °C because of the existence of the single cubic structure and low activation energy. A considerable increase in the conductivity with increasing temperature was observed in Mg-PSZ, which showed higher ionic conductivity than YSZ within the higher temperature range of 1300–1500 °C. A monoclinic-to-tetragonal phase transformation was found in Mg-PSZ and the lattice parameter of the cubic phase increased at 1200 °C. The phase transformation and the large lattice free volume contributed to the significant enhancement of the ionic conductivity of Mg-PSZ at high temperatures.     

Hydrothermal synthesis of Y3NbO7 nanowires for the photocatalytic degradation of omeprazole sodium

Novel Y₃NbO₇ nanowires were successfully synthesized by a facile hydrothermal method using Y(NO₃)₃·6H₂O and Nb₂O₅ as raw materials. X-ray power diffraction (XRD), High resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (UV–vis-DRS), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) techniques were employed to determine the structure, morphology, specific surface area and optical properties of the as-prepared samples. Photocatalytic examination of the samples was carried out using aqueous solution of omeprazole sodium under visible light irradiation. The effects of initial omeprazole sodium concentration and catalyst amount on the photocatalytic degradation were also investigated. Detailed characterization demonstrated that Y₃NbO₇ nanowires have cubic fluorite crystal structure with a diameter of about 20 nm and a length up to several micrometers. Photocatalytic activity tests revealed that omeprazole sodium photocatalytic reactions followed pseudo-first-order kinetics and Y₃NbO₇ nanowires exhibited greater photocatalytic activity than its bulk counterparts.     

Interaction of ceria and ytterbia in air within temperature range 1500 – 600 °C

Phase equilibria and structure transformations in the CeO₂–Yb₂O₃ system have been studied in air within the temperature range 1500 - 600 °C in the full concentration range using X-ray diffraction analysis (XRD) and petrography methods. It was established that the system is characterized by the formation of solid solutions on the basis of cubic modification of Yb₂O₃ (C- type) and fluorite CeO₂ (F- type) separated by two-phase (F + C) region. The systematic study that covered whole composition range excluded formation of new phases. Solubility limits and concentration dependences of lattice parameters were determined for the phases forming in the system.     

Microstructure Evolution and Cation Interdiffusion in Thin Sm2O3 Films on CeO2 Substrates

Samaria (Sm₂O₃) thin films with a thickness of 180 nm were deposited on polycrystalline CeO₂ substrates by pulsed layer deposition to study phase formation and bulk cation interdiffusion in the Ce_1?xSm_xO_2?x/2 system after annealing at temperatures between 987°C and 1266°C. Transmission electron microscopy combined with electron diffraction and analytical techniques was applied for phase determination. The cubic fluorite and cubic bixbyite phases were observed at low and intermediate Sm concentrations. The monoclinic phase occurs only at very high Sm concentrations due to the low Ce‐solubility in Sm₂O₃. Furthermore, a cubic phase with I2₁3 structure was observed at higher Sm concentrations. Cation interdiffusion coefficients were derived from Sm concentration profiles across the Sm₂O₃/CeO₂ interface using the diffusion–couple solution of the diffusion equation. The temperature dependence of interdiffusion coefficients is well described by an Arrhenius‐type relation, which yields an activation enthalpy of 2.26 eV/atom for bulk cation interdiffusion.     

Structure-activity Relation of Fe2O3–CeO2 Composite Catalysts in CO Oxidation

A series of Fe₂O₃–CeO₂ composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe₂O₃–CeO₂ composites with an Fe molar percentage below 0.3 form solid solutions with the CeO₂ cubic fluorite structure, in which the doped Fe³⁺ initially substitutes Ce⁴⁺ in fluorite cubic CeO₂, but then mostly locate in the interstitial sites after a critical concentration of doped Fe³⁺. With an Fe molar percentage between 0.3 and 0.95, the Fe₂O₃–CeO₂ composites are mixed oxides of the cubic fluorite CeO₂ solid solution and the hematite Fe₂O₃. XPS results indicate that CeO₂ is enriched in the surface region of Fe₂O₃–CeO₂ composites. The Fe₂O₃–CeO₂ composites have much higher catalytic activities in CO oxidation than the individual pure CeO₂ and Fe₂O₃, and the Fe_0.1Ce_0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe₂O₃–CeO₂ composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO₂-like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.     

Hydrothermal formation and up‐conversion luminescence of Er3+‐doped GdNbO4

The effect of concentration of Er³⁺ on the up‐conversion and photoluminescence properties of Gd_1.00?xEr_xNbO₄, x=0‐0.50 which has monoclinic fergusonite‐type structure as a main phase has been investigated, using a processing technique based on hydrothermal method. Under weakly basic hydrothermal condition at 240°C for 5 hours, a single phase of fergusonite‐type Gd_1.00?xEr_xNbO₄ solid solution was directly formed as nanocrystals by the substitutional incorporation of Er³⁺ into GdNbO₄ because of the gradual and linear decrease in the lattice parameters of the monoclinic phase corresponding to the Vegard's Law. The gadolinium niobate doped with 2 mol% Er³⁺, Gd_0.98Er_0.02NbO₄ after heating at 1300°C for 1 hour, which has nanocrystalline structure whose crystallite size is around 29 nm, exhibits the highest photoluminescence intensity in the green spectral region, 515‐560 nm under excitation at wavelength of 254 nm. On the other hand, the up‐converted luminescence intensity of the niobate nanocrystals becomes the maximum at the concentration of 20 mol% Er³⁺, Gd_0.80Er_0.20NbO₄ under excitation at 980 nm. These results demonstrate that the material, Er³⁺‐doped GdNbO₄ nanocrystals prepared through hydrothermal route and postheating has potential for up‐converting phosphor.     

Experimental Phase Diagram Determination and Thermodynamic Assessment of the CeO2‐Gd2O3‐CoO System

New phase diagram data and a thermodynamic assessment of the CeO‐Gd₂O₃‐CoO system using the CALPHAD approach are presented. This information is needed to understand the surprisingly low sintering temperature (950°C–1050°C) of CeO₂‐based materials doped with small amounts of transition metal oxide (e.g., CoO). Experimental phase equilibria between 1100°C and 1300°C are reported based on the analysis of annealed and molten samples. No isolated compound exists in the ternary. At 1300°C the Co solubility in the ternary compounds Ce_1?x?yGd_xCo_yO_2?x/2?y (fluorite) is 2.7 mol% and is less than 1 mol% in the Gd_2?xCe_xO_3+x/2 (bixbyite). The Ce solubility in the perovskite GdCoO_3?δ was found to be 1 mol%. The lowest temperature eutectic melt in the ternary has a composition of 57.2 mol% Co and 41.1 mol% Gd melting at an onset temperature of 1303 ± 5°C, which is close to the binary eutectic in the Gd₂O₃‐CoO system at 60 ± 2 mol% Co and 1348 ± 1°C.     

CeO2–YO1.5–NdO1.5 system: An extensive phase relation study

The sub-solidus phase relations in the CeO₂–YO_1.5–NdO_1.5 system have been studied. About 45 compositions in the series Ce_1?x(Y_0.70Nd_0.30)_xO_2?0.5x, Y_1?x(Ce_0.50Nd_0.50)_xO_1.5+0.25x and Nd_1?x(Ce_0.55Y_0.45)_xO_1.5+0.275x were prepared and characterized by powder XRD. In the Ce_1?x(Y_0.70Nd_0.30)_xO_2?0.5x series, there was a gradual transformation from the defective F-type cubic lattice to an ordered C-type phase with increasing x, whereas in the Y_1?x(Ce_0.50Nd_0.50)_xO_1.5+0.25x series, the C-type cubic lattice of yttria was retained over the entire range. In the Nd_1?x(Ce_0.55Y_0.45)_xO_1.5+0.275x system, the compositions with NdO_1.5 content greater than 95 mol% showed coexistence of hexagonal, monoclinic and cubic phases. A biphasic region of monoclinic and C-type cubic phases was observed as NdO_1.5 decreases from 90 to 70 mol%. All the compositions below 70 mol% NdO_1.5, were found to be C-type cubic solid solutions. The phase relations are distinctly characterized by an extensive range of cubic solid solutions, stable under the slow-cooled conditions. To the best of our knowledge, this is the first detailed sub-solidus study reported in CeO₂–YO_1.5–NdO_1.5 system.     

In Situ Diffraction from Levitated Solids Under Extreme Conditions—Structure and Thermal Expansion in the Eu2O3–ZrO2 System

The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500°C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200°C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu₂O₃–ZrO₂ binary system were investigated, including the high‐temperature order–disorder transformation in Eu₂Zr₂O₇. The disordered fluorite phase is found to be stable above 1900°C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu₂Zr₂O₇ show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6–12.0 × 10^?6 C^?1. These studies open new vistas for in situ exploration of complex structural changes in high‐temperature materials.     

Vapor-Phase Dehydration of 1,3-butanediol over CeO2–ZrO2 Catalysts

The dehydration of 1,3-butanediol was investigated over CeO₂–ZrO₂ catalysts prepared by impregnation at temperatures of 325–375 °C. Pure CeO₂ selectively catalyzed the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol, while pure ZrO₂, which was less active than pure CeO₂, catalyzed the dehydration to 3-buten-1-ol. In the CeO₂/ZrO₂ catalyst in which CeO₂ was supported on zirconia, the presence of a small amount of CeO₂ suppressed the formation of 3-buten-1-ol and induced the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol and the subsequent dehydrogenation of 3-buten-2-ol to form 3-buten-2-one and butanone. The activity would be related to the redox features of CeO₂. The monoclinic phase of zirconia support decreased while the cubic CeO₂ phase increased as CeO₂ content was increased. In contrast, in the ZrO₂/CeO₂ catalyst in which ZrO₂ was supported on cubic CeO₂, only the cubic CeO₂ phase was observed and ZrO₂ species appeared in the form of a solid solution of CeO₂–ZrO₂ with fluorite structure. Regardless of zirconia loading, ZrO₂ species did not affect the catalytic activity of ZrO₂/CeO₂, which was controlled by CeO₂ species.     

Large recoverable energy storage density and low sintering temperature in potassium‐sodium niobate‐based ceramics for multilayer pulsed power capacitors

Multilayer pulsed power ceramic capacitors require that dielectric ceramics possess not only large recoverable energy storage density (W_rec) but also low sintering temperature (<950°C) for using the inexpensive metals as the electrodes. However, lead‐free bulk ceramics usually show low W_rec (<2 J/cm³) and high sintering temperature (>1150°C), limiting their applications in multilayer pulsed power ceramic capacitors. In this work, large W_rec (~4.02 J/cm³ at 400 kV/cm) and low sintering temperature (940°C) are simultaneously achieved in 0.9(K_0.5Na_0.5)NbO₃–0.1Bi(Mg_2/3Nb_1/3)O₃–1.0 mol% CuO ceramics prepared using transition liquid phase sintering. W_rec of 4.02 J/cm³ is 2‐3 times as large as the reported value of other (Bi_0.5Na_0.5)TiO₃ and BaTiO₃‐based lead‐free bulk ceramics. The results reveal that 0.9(K_0.5Na_0.5)NbO₃–0.1Bi(Mg_2/3Nb_1/3)O₃–1.0 mol% CuO ceramics are promising candidates for fabricating multilayer pulsed power ceramic capacitors.     

Processing of 0.7BaTiO3–0.3BiScO3 Solid‐Solution Coatings

Coatings with the 0.7BaTiO₃–0.3BiScO₃ solid‐solution composition were formed on palladium and single‐crystal (001) SrTiO₃ substrates using a polymeric metal citrate precursor. Solutions of TiOCl₂, Ba(NO₃)₂, Sc(NO₃)₃, and Bi(NO₃)₃ were mixed with citric acid and polymerized with ethylene glycol. Stable mixed‐metal citrate solutions were formed at pH > 9 and used for coatings. The phase and composition of powders and coatings were characterized using DTA, TGA, SEM, TEM, and X‐ray diffraction. Single‐phase cubic 0.7BaTiO₃–0.3BiScO₃ solid solutions formed at 600°C. Coatings on Pd using precursors doped with 5 wt% lithium nitrate were dense after sintering at 950°C/1 h. Coatings without lithium nitrate required 1050°C/50 h to densify. Coatings on SrTiO₃ heat‐treated at 1150°C were dense but formed a (Sc,Ti)‐rich second phase.     

Microstructural,electrophysical and gas-sensing properties of CeO2–Y2O3 thin films obtained by the sol-gel process

Nanopowders and thin films of (СeO₂)_1-x(Y₂O₃)_x composition (x = 0.10, 0.15 and 0.20) were obtained by the sol-gel process, using hydrolytically active complexes of the metal alkoxoacetylacetonate class [M(C₅H₇O₂)_3-y(C₅H₁₁Oⁱ)_y] (M = Ce³⁺ and Y³⁺) as precursors. The impact of the chemical composition and crystallization conditions on the microstructure, electrophysical and chemosensory characteristics of the obtained planar-type solid electrolytes was studied. The prospects of the thin-film nanostructures obtained as receptor components of resistive oxygen sensors, as well as of electrolytes of planar-type intermediate-temperature solid oxide fuel cells (SOFC) have been shown. It has been found that (CeO₂)_0.90(Y₂O₃)_0.10 thin films demonstrate the maximum values of electrical conductivity (550 °C) and the highest sensory response when detecting oxygen (concentration range 1–20%, operating temperature range 300–450 °C).     

Impact of ZrO2 alloying on thermo-mechanical properties of Gd3NbO7

The ZrO₂ alloying effect is widely used to optimize the thermo-mechanical properties of potential thermal barrier coatings. In this study, dense x mol% ZrO₂-Gd₃NbO₇ with C222₁ space group were manufactured via a solid-state reaction. The crystalline structure was determined through X-ray diffraction and Raman spectroscopy, when the surface morphology was observed by scanning electron microscopy. ZrO₂-Gd₃NbO₇ had identical orthorhombic crystal structures, and there was no second phase. The crystalline structure of ZrO₂-Gd₃NbO₇ shrunk with the increasing ZrO₂ content as indicated by XRD and Raman results. The heat capacity and thermal diffusivity of ZrO₂-Gd₃NbO₇ were 0.31–0.43 J g⁻¹ K⁻¹ (25–900 °C) and 0.25–0.70 mm²/s (25–900 °C), respectively. It was found that ZrO₂-Gd₃NbO₇ had much lower thermal conductivity (1.21–1.82 W m⁻¹ K⁻¹, 25–900 °C) than YSZ (2.50–3.00 W m⁻¹ K⁻¹) and La₂Zr₂O₇ (1.50–2.00 W m⁻¹ K⁻¹). The thermal expansion coefficients (TECs) were higher than 10.60 × 10⁻⁶ K⁻¹ (1200 °C), which were better than that of YSZ (10.00 × 10⁻⁶ K⁻¹) and La₂Zr₂O₇ (9.00 × 10⁻⁶ K⁻¹). The mechanical properties of Gd₃NbO₇ change little with the increasing ZrO₂ content, Vickers hardness was about 10 GPa, and Young's modulus was about 190 GPa, which was lower than YSZ (240 GPa). Compared with previous work about alloying effects, much lower thermal conductivity was obtained. Due to the high melting point, high hardness, low Young's modulus, ultralow thermal conductivity and high TECs, it is believed that ZrO₂-Gd₃NbO₇ is promising TBCs candidate.