Thermal properties of La2Zr2O7 double-layer thermal barrier coatings

La₂Zr₂O₇ is a promising thermal barrier coating (TBC) material. In this work, La₂Zr₂O₇ and 8YSZ-layered TBC systems were fabricated. Thermal properties such as thermal conductivity and coefficient of thermal expansion were investigated. Furnace heat treatment and jet engine thermal shock (JETS) tests were also conducted. The thermal conductivities of porous La₂Zr₂O₇ single-layer coatings are 0.50–0.66?W?m^?1?°C^?1 at the temperature range from 100 to 900°C, which are 30–40% lower than the 8YSZ coatings. The coefficients of thermal expansion of La₂Zr₂O₇ coatings are about 9–10?×?10^?6?°C^?1 at the temperature range from 200 to 1200°C, which are close to those of 8YSZ at low temperature range and about 10% lower than 8YSZ at high temperature range. Double-layer porous 8YSZ plus La₂Zr₂O₇ coatings show a better performance in thermal cycling experiments. It is likely because porous 8YSZ serves as a buffer layer to release stress.     

Thermal cycling performance of La2Ce2O7/50 vol.% YSZ composite thermal barrier coating with CMAS corrosion

La₂Ce₂O₇ (LC) is receiving increasing attention due to its lower thermal conductivity, better phase stability and higher sintering resistance than yttria partially stabilized zirconia (YSZ). However, the low fracture toughness and the sudden drop of CTE at approximately 350?°C greatly limit its application. In this study, the LC/50?vol.% YSZ composite TBC was deposited by supersonic atmospheric plasma spraying (SAPS). Compared to YSZ or double layered LC/YSZ coating, the thermal cycling life of LC/50?vol.% YSZ coating with CMAS attack increased by 93% or 91%. The latter possessed higher fracture toughness (1.48?±?0.26?MPa?m^1/2) than LC (0.72?±?0.15?MPa?m^1/2) and better CMAS corrosion resistance than YSZ owing to the formation of Ca₂(La_xCe_1-x)₈(SiO₄)₆O_6–4x with <001> orientation perpendicular to the coating surface. The sudden CTE decrease of LC was fully suppressed in LC/50?vol.% YSZ coating due to the change of temperature dependent residual stresses induced by YSZ.     

Preparation of ultralow thermal conductivity (Mg0.5Ca0.3Ba0.2) (AlSi)2O8 ceramics

A type of nonequimolar multicomponent ceramic solid solution (Mg_0.5Ca_0.3Ba_0.2) (AlSi)₂O₈ with a low thermal conductivity was prepared through solid-state synthesis. Results show that the (Mg_0.5Ca_0.3Ba_0.2) (AlSi)₂O₈ solid solution exhibits excellent high-temperature stability and an ultralow thermal conductivity (.3676 W m⁻¹ K⁻¹), far lower than widely used 3YSZ (2.9 W m⁻¹ K⁻¹), La₃NbO₇ (1.5 W m⁻¹ K⁻¹), and Gd₂Zr₂O₇ (1.28 W m⁻¹ K⁻¹). Furthermore, the Young modulus of the final product is 64.56 GPa. Therefore, the proposed ceramic solid solution provides a new research direction for ultralow thermal conductivity materials and has a practical application value for the field of wall thermal insulation.     

Enhanced doping effects of multielement on anisotropic thermal expansion in ZrO2 with new compositions

Coefficient of thermal expansion (CTE) of a solid material plays a critical role for a variety of high temperature applications such as thermal barrier coating (TBC) systems during the thermal cycling process. Ceramics contain ionic bonds; hence they tend to exhibit lower CTE values than alloys/metals. Developing new ceramic thermal barrier materials using promising dopants and compositions that have higher CTE values than the conventional 6-8 wt% Y₂O₃ stabilized ZrO₂(8YSZ) will contribute to the decrease in thermal expansion mismatch between a typical ceramic 8YSZ (10 ~ 11 × 10⁻⁶°C⁻¹) top coat and a metal alloy based bond coat such as NiCrAlY (14 ~ 17×10⁻⁶°C⁻¹, Padture et al., Science, 2002;296:280–4; Liang et al., J Mater Sci Technol, 2011;27(5):408–14), which is highly desirable. This work reports design, modeling, synthesis, and characterization of promising new compositions based on Dy³⁺, Al³⁺, and Ce⁴⁺-doped YSZ that consist of the tetragonal structure and have an enhanced thermal expansion than 8YSZ. The intrinsic CTE at the atomic level has been investigated via molecular dynamics (MD) simulation. The atomic scale analysis provides new insights into the enhanced doping effects of multiple trivalent and tetravalent cations on the lattice structure, lattice energy, and thermal expansion in ZrO₂. The calculated lattice energy becomes smaller with the incorporation of Dy³⁺, Al³⁺, and Ce⁴⁺ions, which corresponds strongly to the increase in CTE. The crystalline size is reduced due to the incorporation of the Al³⁺ and Ce⁴⁺, whereas the sintering resistance is enhanced ascribed to the addition of Dy³⁺ and Al³⁺. Doping Dy³⁺, Al³⁺, and Ce⁴⁺ cations to YSZ increased the CTE value of YSZ and for Dy_0.03Y_0.075Zr_0.895O_1.948, the CTE is 12.494 × 10⁻⁶°C⁻¹ at 900°C, which has an 11% increase, as compared with that of 8YSZ.     

Fabrication of La2Zr2O7 ceramic fibers via electrospinning method using different La2O3 precursors

Despite La₂Zr₂O₇ ceramic fiber has been fabricated by electrospinning method, the effects of thermal pyrolysis process on the microstructures and properties of the fibers have seldom been considered. Three La₂O₃ precursors were used to prepare La₂Zr₂O₇ ceramic fibers. Phase transformation of La₂Zr₂O₇ ceramic fibers were characterized by XRD and Raman spectra. The influence of the decomposition process on the microstructure of the fibers was studied by TG/DSC, XPS and SEM. The results show that slow weight loss leads to smaller grain size which could obtain higher strength fibers while fast weight loss could develop pores which are benefit to the decrease of the thermal conductivity.     

Phase stability and thermo-physical properties of ZrO2-CeO2-TiO2 ceramics for thermal barrier coatings

The properties of ZrO₂ co-stabilized by CeO₂ and TiO₂ ceramic bulks were investigated for potential thermal barrier coating (TBC) applications. Results showed that the (Ce_0.15Ti_x)Zr_0.85-xO7 (x?=?0.05, 0.10, 0.15) compositions with single tetragonal phase were more stable than the traditional 8YSZ at 1573?K. These compositions also showed a large thermal expansion coefficient (TEC) and a high fracture toughness, which were comparable to those of YSZ. However, the phase stability, fracture toughness and sintering resistance of the CeO₂-TiO₂-ZrO₂ system showed a decline tendency with the increase of TiO₂ content. The TEC of the ceramic bulks decreased with increase of TiO₂ content as well because the crystal energy was enhanced with increasing substitution of Zr⁴⁺ by smaller Ti⁴⁺. The (Ce_0.15Ti_0.05)Zr_0.8O₂ had the best comprehensive properties among the (Ce_0.15Ti_x)Zr_0.85-xO₂ compositions as well as a low thermal conductivity. Therefore, it can be explored as a TBC candidate material for high-temperature applications.     

Thermal stability of plasma-sprayed La2Ce2O7/YSZ composite coating

A composite coating composed of La₂Ce₂O₂ (LCO) and yttria-stabilized zirconia (YSZ) in a weight ratio of 1:1 was deposited by the plasma spraying using a blended YSZ and LCO powders, and the stability of the LCO/YSZ interface exposed to a high temperature was investigated. The LCO/YSZ deposits were exposed at 1300 °C for different durations. The microstructure evolution at the LCO/YSZ interface was investigated by quasi-in-situ scanning electron microscopy assisted by X-ray energy-dispersive spectrum analyses and X-ray diffraction measurements. At an exposure temperature of 1300 °C, the grain morphology of LCO splats in contact with YSZ splats changed from columnar grains to quasi-axial grains with interface healing, and some grains tended to disappear during the thermal exposure. The results indicate that the phases in LCO–YSZ composite coating are not stable at 1300 °C. The element La in the LCO splat diffused towards the adjacent YSZ splat during the exposure, generating the reaction product layers composed of La₂Zr₂O₇ between the LCO and YSZ splats. After exposed for 200 h, the composite coating consisted of a mixture of mainly La₂Zr₂O₇ and CeO₂ and a minor amount of YSZ, accounting for the unusual decrease in the thermal conductivity at the late stage of exposure.     

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.     

Influence of B-site substituent Ce on thermophysical,oxygen diffusion,and mechanical properties of La2Zr2O7

Pyrochlore-type La₂Zr₂O₇ (LZ) is a promising candidate for high-temperature thermal barrier coatings (TBCs). However, its thermal expansion coefficient and low fracture toughness are not optimal for such application and thus, need to be improved. In this study, we systematically report the effect of CeO₂ addition on phase formation, oxygen-ion diffusion, and thermophysical and mechanical properties of full compositions La₂(Zr₁?_xCe_x)₂O₇ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1). La₂(Zr₁?_xCe_x)₂O₇ exhibits a pyrochlore structure at x ≤ 0.3, while a fluorite structure is observed outside this range. With the increase in CeO₂ content, thermal expansion coefficient and oxygen-ion diffusivity in La₂(Zr₁?_xCe_x)₂O₇ are increased. Oxygen-ion diffusivity of La₂(Zr₁?_xCe_x)₂O₇ is two orders of magnitude less than that of classical 8YSZ. Among La₂(Zr₁?_xCe_x)₂O₇ compounds, La₂(Zr_0.7Ce_0.3)₂O₇ and La₂(Zr_0.5Ce_0.5)₂O₇ exhibit relatively low oxygen diffusivities. The composition La₂(Zr_0.5Ce_0.5)₂O₇ presents the lowest thermal conductivity due to the strongest phonon scattering and also the highest fracture toughness due to the solid-solution toughening. The highest sintering resistance is achieved by the composition La₂(Zr_0.7Ce_0.3)₂O₇ because of its ordered pyrochlore structure and high atomic mass of Ce. Based on these results, the compositions La₂(Zr_0.5Ce_0.5)₂O₇ and La₂(Zr_0.7Ce_0.3)₂O₇ are alternatives for classical 8YSZ for TBC materials operating at ultrahigh temperatures.     

A novel porous La2Zr2O7 ceramic aerogels with ultralow thermal conductivity and photocatalytic property

Porous La₂Zr₂O₇ ceramic aerogels (CAs) were prepared by sol-gel template method and thermal treated process. The microstructure and crystallisation behavior of the samples were systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. The results indicated that the as-prepared porous La₂Zr₂O₇ CAs had a single-phase pyrochlore structure with typical three-dimensional (3-D) porous structure. Meanwhile, the formation mechanisms of the as-prepared porous La₂Zr₂O₇ CAs were investigated. At the same time, the as-prepared porous La₂Zr₂O₇ CAs presented an ultralow room-temperature thermal conductivity of 0.07 W/(m K), high specific surface areas of 325.17 m²/g, and a relatively high compressive strength of 11.95 MPa. What's more, the as-prepared porous La₂Zr₂O₇ CAs possessed ideal photocatalytic activities due to its high crystallinity, large surface area as well as unique 3-D porous structure. Therefore, the present work is proposing some new insight to prepare rare-earth zirconates CAs with porous structures for thermal insulation and dye degradation applications.     

Structure evolution,thermal properties and sintering resistance of promising thermal barrier coating material La2(Zr0.75Ce0.25)2O7

Rare-earth doped zirconates are promising candidate materials for high-performance thermal barrier coatings (TBCs). The phase and microstructure stability is an important issue for the materials that must be clarified, which is related to the long-term stable work of TBCs at high temperatures. In this work, La₂(Zr_0.75Ce_0.25)₂O₇ (LCZ) ceramic coatings prepared by atmospheric plasma spraying present a metastable fluorite phase, which can transform into stable pyrochlore under high-temperature annealing. The detailed structure evolution of the ceramic coatings is characterized systematically by SEM, XRD and Raman. The associated thermal properties of LCZ ceramics were also reported. Results show that LCZ ceramic has an ultralow thermal conductivity (0.65 W/m·K, 1200 °C), which is only 1/3 of that of yttria-stabilized zirconia (YSZ). The thermal expansion coefficients of LCZ ceramic increase from 9.68 × 10^-6 K^-1 to 10.7 × 10^-6 K^-1 (300 - 1500 °C), which are relatively larger than those of La₂Zr₂O₇. Besides, Long-term sintering demonstrates that LCZ ceramic coating has preferable sintering resistance at 1500 °C, which is desirable for TBC applications.     

High entropy (LaCeSmEuNd)2Zr2O7 ceramic aerogel with low thermal conductivity and excellent structural heat resistance

Dimensions and thermal insulation properties of nanoporous ceramics are unstable at high temperatures due to structural disruptions. This work prepared high entropy (LaCeSmEuNd)₂Zr₂O₇ ceramic aerogel via non-alkoxide sol-gel, supercritical drying, and calcination. XRD and EDS analysis showed that the (LaCeSmEuNd)₂Zr₂O₇ ceramic existed as a single phase. SEM images demonstrated the successful synthesis of aerogel structure. After two hours of annealing at 1200 °C, the cylindrical sample pressed from (LaCeSmEuNd)₂Zr₂O₇ ceramic aerogel had a compressive strength of 58.75 MPa, and its diameter shrinkage was 0.56%, whereas the La₂Zr₂O₇ reached 13.68%. The thermal diffusivity of annealed (LaCeSmEuNd)₂Zr₂O₇ was as low as 0.119 mm² s^?1, and its thermal conductivity at room temperature was 0.073 W·m^?1 K^?1, which was attributed to lattice disorder, stable porous structure, and abundance of grain boundaries caused by high entropy effects. Extending the high entropy effect to ceramic nano-insulation products is beneficial for enhancing their thermal stability.     

Phase structure and thermophysical properties of co-doped La2Zr2O7 ceramics for thermal barrier coatings

La₂Zr₂O₇ has high melting point, low thermal conductivity and relatively high thermal expansion which make it suitable for application as high-temperature thermal barrier coatings. Ceramics including La₂Zr₂O₇, (La_0.7Yb_0.3)₂(Zr_0.7Ce_0.3)₂O₇ and (La_0.2Yb_0.8)₂(Zr_0.7Ce_0.3)₂O₇ were synthesized by solid state reaction. The effects of co-doping on the phase structure and thermophysical properties of La₂Zr₂O₇ were investigated. The phase structures of these ceramics were identified by X-ray diffraction, showing that the La₂Zr₂O₇ ceramic has a pyrochlore structure while the co-doped ceramics (La_0.7Yb_0.3)₂(Zr_0.7Ce_0.3)₂O₇ and the (La_0.2Yb_0.8)₂(Zr_0.7Ce_0.3)₂O₇ exhibit a defect fluorite structure, which is mainly determined by ionic radius ratio r(A_av.³⁺)/r(B_av.⁴⁺). The measurements for thermal expansion coefficient and thermal conductivity of these ceramics from ambient temperature to 1200 °C show that the co-doped ceramics (La_0.7Yb_0.3)₂(Zr_0.7Ce_0.3)₂O₇ and (La_0.2Yb_0.8)₂(Zr_0.7Ce_0.3)₂O₇ have a larger thermal expansion coefficient and a lower thermal conductivity than La₂Zr₂O₇, and the (La_0.2Yb_0.8)₂(Zr_0.7Ce_0.3)₂O₇ shows the more excellent thermophysical properties than (La_0.7Yb_0.3)₂(Zr_0.7Ce_0.3)₂O₇ due to the increase of Yb₂O₃ content.     

Process induced alignment of carbon nanotube decreases longitudinal thermal conductivity of Al2O3 based porous composites

Alumina (Al₂O₃) based porous composites, reinforced with zirconia (ZrO₂), 3 and 8 mol% Y₂O₃ stabilized ZrO₂ (YSZ) and 4 wt% carbon nanotube (CNT) are processed via spark plasma sintering. The normalized linear shrinkage during sintering process of Al₂O₃-based composite shows minimum value (19.2–20.4%) for CNT reinforced composites at the temperature between 1650 °C and 575 °C. Further, the combined effect of porosity, phase-content and its crystallite size in sintered Al₂O₃-based porous composite have elicited lowest thermal conductivity of 1.2 Wm⁻¹K⁻¹ (Al₂O₃-8YSZ composite) at 900 °C. Despite high thermal conductivity of CNT (∼3000 Wm⁻¹K⁻¹), only a marginal thermal conductivity increase (∼1.4 times) to 7.3–13.4 Wm⁻¹K⁻¹ was observed for CNT reinforced composite along the longitudinal direction at 25 °C. The conventional models overestimated the thermal conductivity of CNT reinforced composites by up to ∼6.7 times, which include the crystallite size, porosity, and interfacial thermal resistance of Al₂O₃, YSZ and, CNT. But, incorporation of a new process induced CNT-alignment factor, the estimated thermal conductivity (of <6.6 Wm⁻¹K⁻¹) closely matched with the experimental values. Moreover, the high thermal conductivity (<76.1 Wm⁻¹K⁻¹) of the CNT reinforced porous composites along transverse direction confirms the process induced alignment of CNT in the spark plasma sintered composites.     

The effect of ZrO2 alloying on the microstructures and thermal properties of DyTaO4 for high-temperature application

High fracture toughness of 8 YSZ (8 wt% yttria-stabilized zirconia) is linked to its ferroelastic toughening mechanism. In this work, the similar ferroelastic domain is detected in monoclinic Dy_1−xTa_1−xZr_2xO₄ ceramics, which derives from the ferroelastic transformation between the high-temperature tetragonal (t) and low-temperature monoclinic (m) phase. The lowest thermal conductivity of Dy_1−xTa_1−xZr_2xO₄ ceramics is reduced by 30% compared with 8 YSZ, and the largest thermal expansion coefficients (TECs) is up to 11 × 10⁻⁶ K⁻¹ at 1200°C, which is comparable to that of 8 YSZ. Notably, the systematic investigations containing phase, microstructure, thermophysical properties of Dy_1−xTa_1−xZr_2xO₄ ceramics will provide guidance for its high-temperature application, especially as thermal barrier coatings.     

Production of Re doped La2Zr2O7 based TBCs and numerical analysis of their use on IC engine piston surface

In this study, first of all, a metallic bond layer was coated on the metal substrate using the HVOF method. Then, Gd and Yb doped La₂Zr₂O7 powders, which were specially produced to obtain a low thermal conductivity value, were coated on the metallic bond layer by atmospheric plasma spraying method. The coatings were produced in single-layer and double-layer designs using YSZ as the buffer layer. In the microstructure analysis, it was observed that the coatings exhibited the characteristic microstructure properties of the materials produced by atmospheric plasma spraying method. In the phase analysis, it was found that the Gd and Yb doped La₂Zr₂O₇ was in the form of defect fluorite type structure after plasma spraying. The thermal conductivity of the YSZ coating ranged from 0.88 to 1.00 W/mK, while the thermal conductivity of the doped La₂Zr₂O₇ coatings was measured between 0.38 and 0.68 W/mK. Especially, the lowest thermal conductivity values were obtained in the double-layer Gd doped coating. As a result of modeling these coatings on the piston surface of a diesel engine using the finite element method, it was found that the maximum and minimum surface temperatures of the pistons increased by 69% and 60%, respectively. There was also a reduction of up to 6.5% in the temperature of the piston substrate surface.     

Thermal cycling behavior and bonding strength of single-ceramic-layer Sm2Zr2O7 and double-ceramic-layer Sm2Zr2O7/8YSZ thermal barrier coatings deposited by atmospheric plasma spraying

The single-ceramic-layer (SCL) Sm₂Zr₂O₇ (SZO) and double-ceramic-layer (DCL) Sm₂Zr₂O₇ (SZO)/8YSZ thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying on nickel-based superalloy substrates with NiCoCrAlY as the bond coat. The mechanical properties of the coatings were evaluated using bonding strength and thermal cycling lifetime tests. The microstructures and phase compositions of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that both coatings demonstrate a well compact state. The DCL SZO/8YSZ TBCs exhibits an average bonding strength approximately 1.5 times higher when compared to the SCL SZO TBCs. The thermal cycling lifetime of DCL SZO/8YSZ TBCs is 660 cycles, which is much longer than that of SCL 8YSZ TBCs (150 cycles). After 660 thermal cycling, only a little spot spallation appears on the surface of the DCL SZO/8YSZ coating. The excellent mechanical properties of the DCL LZ/8YSZ TBCs can be attributed to the underlying 8YSZ coating with the combinational structures, which contributes to improve the toughness and relieve the thermal mismatch between the ceramic layer and the metallic bond coat at high temperature.     

Effect of geometric parameter on thermal stress generation in fabrication process of double-ceramic-layers thermal barrier coating system

In this work, quenching stress generated during the deposition process and the Coefficient of Thermal Expansion (CTE) thermal mismatch stress produced during the cooling down process of Double-Ceramic-Layers Thermal Barrier Coating System (DCL-TBCs) have been intensively examined. The thickness ratio of Lanthanum Zirconate (LZ, La₂Zr₂O₇) coating to stabilized Zirconia (YSZ, ZrO₂-8%Y₂O₃) coating, have been theoretically analyzed. In addition, DCL-TBCs specimens with different thickness ratio of LZ to YSZ coatings were fabricated, to study the effect of this thickness ratio by specimen curvature and crack density analysis. Meanwhile, Finite Element Method (FEM) has been carried out to validate results obtained theoretically. The results reveal that by comparison to CTE thermal mismatch stress, quenching stress has remarkable effect on total thermal stress. By increasing thickness ratio of YSZ to LZ coatings, average thermal stress and crack densities in YSZ and LZ coatings increased. Nevertheless, the curvature ratio of DCL-TBCs specimen decreases.     

Fabrication and characterization of novel excellent thermal-protection Gd2Zr2O7/ZrO2 composite ceramic fibers with different proportions of Gd2Zr2O7

Three kinds of Gd₂Zr₂O₇/ZrO₂ (GZC) composite fibers with different proportions of Gd₂Zr₂O₇ were prepared by electrospinning method through changing the amount of Gd³⁺ in precursor solutions. The thermal decomposition, crystallization process, high temperature stability and heat-conducting properties of GZC fibers were fully characterized. The results showed that there were three crystalline phases, tetragonal phase ZrO₂, cubic phase ZrO₂ and defect fluorite phase Gd₂Zr₂O₇ in all the GZC fibers. The content of Gd₂Zr₂O₇ increased gradually with the increase of Gd³⁺ in precursor solutions which led to the gradual slowing down of grain growth rate, the decrease of thermal conductivity and the increase of high temperature stability of the obtained composite fibers. The thermal conductivities of all the GZC fiber sheets were lower than that of 7YSZ fiber sheet. The sheets of all the GZC fibers could keep the high temperature stability up to 1300 °C.     

Electronic structure and thermal properties of Sm3+-doped La2Zr2O7: First-principles calculations and experimental study

By applying the first-principles calculation, the electronic structure, mechanical and thermal properties of Sm³⁺-doped La₂Zr₂O₇ were investigated, and experiments were carried out to verify the theoretical results. As the Sm³⁺ doping rate increases, the lattice parameters decrease while the theoretical density increases. The doping of Sm³⁺ promotes the transformation from pyrochlore structure to defective fluorite structure. The Young's modulus of pure La₂Zr₂O₇ shows obvious anisotropy, while it tends to be isotropy with the doping of Sm³⁺. The calculated theoretical hardness is positively correlated with the doping rate, yet due to the solid solution strengthening effect, the materials with doping rate of 50% get the highest hardness. Based on the calculations and experiments, the optimal Sm³⁺ doping rate of La₂Zr₂O₇ is 50%. LaSmZr₂O₇ has hardness of 11.35 GPa, the thermal conductivity of 1.35 W/(m·K) at 1173 K, and the thermal expansion coefficient of 10.12 × 10⁻⁶/K at 1173 K. The above results indicate that LaSmZr₂O₇ has good mechanical and thermal properties, which provides new ideas for the selection of thermal barrier coating materials.