Improvement strategy on thermophysical properties of A₂B₂O₇-type rare earth zirconates for thermal barrier coatings applications: A review

Abstract

The A₂B₂O₇-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating (TBC) materials because of their low sintering rate, improved phase stability, and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments. This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines. Based on the first principles, molecular dynamics, and new data-driven calculation approaches, doping and high-entropy strategies have now been adopted in advanced TBC materials design. In this paper, the solid-state heat transfer mechanism of TBCs is explained from two aspects, including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature. This paper also provides new insights into design considerations of adaptive TBC materials, and the challenges and potential breakthroughs are further highlighted for extreme environmental applications. Strategies for improving thermophysical performance are proposed in two approaches: defect engineering and material compositing.

Keywords

rare earth zirconates / thermal barrier coatings / defect engineering / doping and compositing / thermal conductivity / thermal expansion

References

[1] Chen HF, Zhang C, Liu YC, et al. Recent progress in thermal/environmental barrier coatings and their corrosion resistance. Rare Met., 2020, 39(5): 498.

[2] Padture NP, Gell M, Jordan EH. Thermal barrier coatings for gas-turbine engine applications. Science, 2002, 296(5566): 280.

[3] Padture NP. Advanced structural ceramics in aerospace propulsion. Nat. Mater., 2016, 15, 804.

[4] Levi CG, Hutchinson JW, Vidal-Sétif MH, Johnson CA. Environmental degradation of thermal-barrier coatings by molten deposits. MRS Bull., 2012, 37(10): 932.

[5] Clarke DR, Levi CG. Materials design for the next generation thermal barrier coatings. Annu. Rev. Mater. Res., 2003, 33, 383.

[6] Liu ZG, Zhang WH, Ouyang JH, Zhou Y. Novel double-ceramic-layer (La_0.8Eu_0.2)₂Zr₂O₇/YSZ thermal barrier coatings deposited by plasma spraying. Ceram. Int., 2014, 40(7): 11277.

[7] Liu ZG, Zhang WH, Ouyang JH, Zhou Y. Novel thermal barrier coatings based on rare-earth zirconates/YSZ double-ceramic-layer system deposited by plasma spraying. J. Alloys Compd., 2015, 647, 438.

[8] Schulz U, Leyens C, Fritscher K, et al. Some recent trends in research and technology of advanced thermal barrier coatings. Aerosp. Sci. Technol., 2003, 7(1): 73.

[9] Cao XQ, Vassen R, Stoever D. Ceramic materials for thermal barrier coatings. J. Eur. Ceram. Soc., 2004, 24(1): 1.

[10] Vassen R, Cao XQ, Tietz F, Basu D, Stöver D. Zirconates as new materials for thermal barrier coatings. J. Am. Ceram. Soc., 2000, 83(8): 2023.

[11] Zhao M, Pan W, Wan CL, Qu ZX, Li Z, Yang J. Defect engineering in development of low thermal conductivity materials: A review. J. Eur. Ceram. Soc., 2017, 37(1): 1.

[12] Gild J, Samiee M, Braun JL, et al. High-entropy fluorite oxides. J. Eur. Ceram. Soc., 2018, 38(10): 3578.

[13] Lackey WJ, Stinton DP, Cerny GA, Schaffhauser AC, Fehrenbacher LL. Ceramic coatings for advanced heat engines-A review and projection. Adv. Ceram. Mater., 1987, 2(1): 24.

[14] Xu CH, Jin HY, Zhang QF, et al. A novel Co-ions complexation method to synthesize pyrochlore La₂Zr₂O₇. J. Eur. Ceram. Soc., 2017, 37(8): 2871.

[15] Zhang HS, Xu Q, Wang FC, Liu L, Wei Y, Chen XG. Preparation and thermophysical properties of (Sm_0.5La_0.5)₂Zr₂O₇ and (Sm_0.5La_0.5)₂(Zr_0.8Ce_0.2)₂O₇ ceramics for thermal barrier coatings. J. Alloys Compd., 2009, 475(1–2): 624.

[16] Padture NP, Klemens PG. Low thermal conductivity in garnets. J. Am. Ceram. Soc., 1997, 80(4): 1018.

[17] C.J. Friedrich, R. Gadow, and M.H. Lischka, Lanthanum hexaaluminate thermal barrier coatings, [in] 25th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Florida, 2001, p. 375.

[18] G.W. Schafer and R. Gadow, Lanthane aluminate thermal barrier coating, [in] 23nd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures B: Ceramic Engineering and Science Proceedings, Hoboken, 1999, p. 291.

[19] Chen L, Hu MY, Wu P, Feng J. Thermal expansion performance and intrinsic lattice thermal conductivity of ferroelastic RETaO₄ ceramics. J. Am. Ceram. Soc., 2019, 102(8): 4809.

[20] Chen L, Song P, Feng J. Influence of ZrO₂ alloying effect on the thermophysical properties of fluorite-type Eu₃TaO₇ ceramics. Scripta Mater., 2018, 152, 117.

[21] Yang J, Pan W, Han Y, Zhao M, Huang MZ, Wan CL. Mechanical properties, oxygen barrier property, and chemical stability of RE₃NbO₇ for thermal barrier coating. J. Am. Ceram. Soc., 2020, 103(4): 2302.

[22] Shi DD, Cao ZB, Huang YH, et al. Highly efficient thermal insulation in crystalline weberites RE₃NbO₇ (RE = La, Nd, Sm, Eu, Gd) with glass-like thermal conductivity. Ceram. Int., 2022, 48(2): 2686.

[23] Morgan PED, Marshall DB. Ceramic composites of monazite and alumina. J. Am. Ceram. Soc., 1995, 78(6): 1553.

[24] Vassen R, Kerkhoff G, Stöver D. Development of a micromechanical life prediction model for plasma sprayed thermal barrier coatings. Mater. Sci. Eng. A, 2001, 303(1–2): 100.

[25] S. Akrami, P. Edalati, M. Fuji, and K. Edalati, High-entropy ceramics: Review of principles, production and applications, Mater. Sci. Eng. R Rep., 146(2021), art. No. 100644.

[26] Zhang RZ, Reece MJ. Review of high entropy ceramics: Design, synthesis, structure and properties. J. Mater. Chem. A, 2019, 7(39): 22148.

[27] Wright AJ, Luo J. A step forward from high-entropy ceramics to compositionally complex ceramics: A new perspective. J. Mater. Sci., 2020, 55(23): 9812.

[28] A.J. Wright, Q.Y. Wang, C.Z. Hu, Y.T. Yeh, R.K. Chen, and J. Luo, Single-phase duodenary high-entropy fluorite/pyrochlore oxides with an order-disorder transition, Acta Mater., 211(2021), art. No. 116858.

[29] Zhao ZF, Xiang HM, Dai FZ, Peng ZJ, Zhou YC. (La_0.2Ce_0.2Nd_0.2Sm_0.2Eu_0.2)₂Zr₂O₇: A novel high-entropy ceramic with low thermal conductivity and sluggish grain growth rate. J. Mater. Sci. Technol., 2019, 35(11): 2647.

[30] Divilov S, Eckert H, Hicks D, et al. Disordered enthalpy-entropy descriptor for high-entropy ceramics discovery. Nature, 2024, 625(7993): 66.

[31] Grimvall G. Thermophysical Properties of Materias, 1999, Amsterdam, Elsevier.

[32] Kingery WD, Bowen HK, Uhlmann DR. Introduction to Ceramics, 1976, New York, John Wiley & Sons.

[33] Holland MG. Analysis of lattice thermal conductivity. Phys. Rev., 1963, 132(6): 2461.

[34] Abeles B. Lattice thermal conductivity of disordered semiconductor alloys at high temperatures. Phys. Rev., 1963, 131(5): 1906.

[35] Klemens PG. Thermal resistance due to point defects at high temperatures. Phys. Rev., 1960, 119(2): 507.

[36] Callaway J, von Baeyer HC. Effect of point imperfections on lattice thermal conductivity. Phys. Rev., 1960, 120(4): 1149.

[37] He XD, Li YB, Wang LD, Sun Y, Zhang S. High emissivity coatings for high temperature application: Progress and prospect. Thin Solid Films, 2009, 517(17): 5120.

[38] D.L. Zhao, A. Aili, Y. Zhai, et al., Radiative sky cooling: Fundamental principles, materials, and applications, Appl. Phys. Rev., 6(2019), No. 2, art. No. 021306.

[39] Zhao B, Hu MK, Ao XZ, Chen N, Pei G. Radiative cooling: A review of fundamentals, materials, applications, and prospects. Appl. Energy, 2019, 236, 489.

[40] Liu HZ, Ouyang JH, Liu ZG, Wang YM. Thermo-optical properties of LaMAl₁₁O₁₉ (M=Mg, Mn, Fe) hexaaluminates for high-temperature thermal protection applications. J. Am. Ceram. Soc., 2011, 94(10): 3195.

[41] G.L. Chen, H.Y. Fu, Y.C. Zou, et al., A promising radiation thermal protection coating based on lamellar porous Ca–Cr co-doped Y₃NbO₇ ceramic, Adv. Funct. Mater., 33(2023), No. 47, art. No. 2305650.

[42] Wang SM, Kuang FH, Yan QZ, Ge CC, Qi LH. Crystallization and infrared radiation properties of iron ion doped cordierite glass-ceramics. J. Alloys Compd., 2011, 509(6): 2819.

[43] K. Krieble, T. Schaeffer, J.A. Paulsen, A.P. Ring, C.C.H. Lo, and J.E. Snyder, Mössbauer spectroscopy investigation of Mn-substituted Co–ferrite (CoMn_xFe_2−xO₄), J. Appl. Phys., 97(2005), No. 10, art. No. 10F101.

[44] Subramanian MA, Aravamudan G, Rao GVS. Oxide pyrochlores–A review. Prog. Solid State Chem., 1983, 15(2): 55.

[45] Liu ZG, Ouyang JH, Zhou Y. Preparation and thermophysical properties of (Nd_xGd_1−x)₂Zr₂O₇ ceramics. J. Mater. Sci., 2008, 43(10): 3596.

[46] Liu ZG, Ouyang JH, Zhou Y. Structural evolution and thermophysical properties of (Sm_xGd_1−x)₂Zr₂O₇ (0 ≤ x ≤ 1.0) ceramics. J. Alloys Compd., 2009, 472(1–2): 319.

[47] Liu ZG, Ouyang JH, Zhou Y, Li J, Xia XL. Influence of ytterbium- and samarium-oxides codoping on structure and thermal conductivity of zirconate ceramics. J. Eur. Ceram. Soc., 2009, 29(4): 647.

[48] Liu ZG, Ouyang JH, Zhou Y, Li J, Xia XL. Densification, structure, and thermophysical properties of ytterbium–gadolinium zirconate ceramics. Int. J. Appl. Ceram. Technol., 2009, 6(4): 485.

[49] Wan CL, Zhang W, Wang YF, et al. Glass-like thermal conductivity in ytterbium-doped lanthanum zirconate pyrochlore. Acta Mater., 2010, 58(18): 6166.

[50] Wan CL, Qu ZX, Du AB, Pan W. Order-disorder transition and unconventional thermal conductivities of the (Sm_1−xYb_x)₂Zr₂O₇ series. J. Am. Ceram. Soc., 2011, 94(2): 592.

[51] Ren XR, Wan CL, Zhao M, Yang J, Pan W. Mechanical and thermal properties of fine-grained quasi-eutectoid (La_1−xYb_x)₂Zr₂O₇ ceramics. J. Eur. Ceram. Soc., 2015, 35(11): 3145.

[52] Wu Y, Zheng L, He WT, He J, Guo HB. Effects of Yb³⁺ doping on phase structure, thermal conductivity and fracture toughness of (Nd_1−xYb_x)₂Zr₂O₇. Ceram. Int., 2019, 45(3): 3133.

[53] Zhang HS, Sun K, Xu Q, Wang FC, Liu L. Preparation and thermal conductivity of Sm₂(Zr_0.6Ce_0.4)₂O₇ ceramic. J. Mater. Eng. Perform., 2009, 18(8): 1140.

[54] Yang J, Zhao M, Zhang L, Wang ZY, Pan W. Pronounced enhancement of thermal expansion coefficients of rare-earth zirconate by cerium doping. Scripta Mater., 2018, 153, 1.

[55] Fan QB, Zhang F, Wang FC, Wang L. Molecular dynamics calculation of thermal expansion coefficient of a series of rare-earth zirconates. Comput. Mater. Sci., 2009, 46(3): 716.

[56] Zhou HM, Yi DQ. Effect of rare earth doping on thermo-physical properties of lanthanum zirconate ceramic for thermal barrier coatings. J. Rare Earths, 2008, 26(6): 770.

[57] Wu J, Wei XZ, Padture NP, et al. Low-thermal-conductivity rare-earth zirconates for potential thermal-barrier-coating applications. J. Am. Ceram. Soc., 2002, 85(12): 3031.

[58] Xu Q, Pan W, Wang JD, et al. Preparation and thermophysical properties of Dy₂Zr₂O₇ ceramic for thermal barrier coatings. Mater. Lett., 2005, 59(22): 2804.

[59] Xu Q, Pan W, Wang JD, et al. Rare-earth zirconate ceramics with fluorite structure for thermal barrier coatings. J. Am. Ceram. Soc., 2006, 89(1): 340.

[60] Feng J, Xiao B, Zhou R, Pan W. Thermal conductivity of rare earth zirconate pyrochlore from first principles. Scr. Mater., 2013, 68(9): 727.

[61] Yang J, Shahid M, Zhao M, Feng J, Wan CL, Pan W. Physical properties of La₂B₂O₇ (B = Zr, Sn, Hf and Ge) pyrochlore: First-principles calculations. J. Alloys Compd., 2016, 663, 834.

[62] G.Q. Lan, B. Ouyang, Y.S. Xu, J. Song, and Y. Jiang, Predictions of thermal expansion coefficients of rare-earth zirconate pyrochlores: A quasi-harmonic approximation based on stable phonon modes, J. Appl. Phys., 119(2016), No. 23, art. No. 235103.

[63] X.Q. Wang, X. Bai, W. Xiao, et al., Calculation of thermal expansion coefficient of rare earth zirconate system at high temperature by first principles, Materials, 15(2022), No. 6, art. No. 2264.

[64] Q. Chen, W. Song, Y. Xie, Z.X. Yan, J. Xu, and F. Gao, Thermal expansion coefficient of nonstoichiometric gadolinium zirconate: First-principles calculations and experimental study, J. Phys. Chem. Solids, 178(2023), art. No. 111363.

[65] Joulia A, Vardelle M, Rossignol S. Synthesis and thermal stability of Re₂Zr₂O₇, (Re = La, Gd) and La₂(Zr_1−xCe_x)₂O_7−δ compounds under reducing and oxidant atmospheres for thermal barrier coatings. J. Eur. Ceram. Soc., 2013, 33(13–14): 2633.

[66] Kaliyaperumal C, Sankarakumar A, Palanisamy J, Paramasivam T. Fluorite to pyrochlore phase transformation in nanocrystalline Nd₂Zr₂O₇. Mater. Lett., 2018, 228, 493.

[67] Zhao HB, Levi CG, Wadley HNG. Vapor deposited samarium zirconate thermal barrier coatings. Surf. Coat. Technol., 2009, 203(20–21): 3157.

[68] Yu JH, Zhao HY, Tao SY, Zhou XM, Ding CX. Thermal conductivity of plasma sprayed Sm₂Zr₂O₇ coatings. J. Eur. Ceram. Soc., 2010, 30(3): 799.

[69] Zhao HB, Begley MR, Heuer A, Sharghi-Moshtaghin R, Wadley HNG. Reaction, transformation and delamination of samarium zirconate thermal barrier coatings. Surf. Coat. Technol., 2011, 205(19): 4355.

[70] Aruna ST, Sanjeeviraja C, Balaji N, Manikandanath NT. Properties of plasma sprayed La₂Zr₂O₇ coating fabricated from powder synthesized by a single-step solution combustion method. Surf. Coat. Technol., 2013, 219, 131.

[71] Jiang C, Jordan EH, Harris AB, Gell M, Roth J. Double-layer gadolinium zirconate/yttria-stabilized zirconia thermal barrier coatings deposited by the solution precursor plasma spray process. J. Therm. Spray Technol., 2015, 24(6): 895.

[72] Mahade S, Curry N, Björklund S, Markocsan N, Nylén P. Thermal conductivity and thermal cyclic fatigue of multilayered Gd₂Zr₂O₇/YSZ thermal barrier coatings processed by suspension plasma spray. Surf. Coat. Technol., 2015, 283, 329.

[73] Martena M, Botto D, Fino P, Sabbadini S, Gola MM, Badini C. Modelling of TBC system failure: Stress distribution as a function of TGO thickness and thermal expansion mismatch. Eng. Fail. Anal., 2006, 13(3): 409.

[74] Lehmann H, Pitzer D, Pracht G, Vassen R, Stöver D. Thermal conductivity and thermal expansion coefficients of the lanthanum rare-earth-element zirconate system. J. Am. Ceram. Soc., 2003, 86(8): 1338.

[75] Liu ZG, Ouyang JH, Wang BH, Zhou Y, Li J. Preparation and thermophysical properties of Nd_xZr_1−xO_2−x/2 (x = 0.1, 0.2, 0.3, 0.4, 0.5) ceramics. J. Alloys Compd., 2008, 466(1–2): 39.

[76] Guo YQ, He WT, Guo HB. Thermo-physical and mechanical properties of Yb₂O₃ and Sc₂O₃ co-doped Gd₂Zr₂O₇ ceramics. Ceram. Int., 2020, 46(11): 18888.

[77] Yang RW, Xu J, Wei MY, et al. Rattler effect on the properties of multicomponent rare-earth-zirconate ceramics. Ceram. Int., 2022, 48(19): 28586.

[78] Li MY, Lin CC, Niu YR, Zhang JM, Zeng Y, Song XM. Order–disorder transition and thermal conductivities of the (NdSmEuGd)_(1−x)/2Dy_2xZr₂O₇ series. J. Materiomics, 2023, 9(1): 138.

[79] Zhao FA, Xiao HY, Liu ZJ, Li SA, Zu XT. A DFT study of mechanical properties, thermal conductivity and electronic structures of Th-doped Gd₂Zr₂O₇. Acta Mater., 2016, 121, 299.

[80] G. Lan, P.F. Ou, C. Chen, and J. Song, A complete computational route to predict reduction of thermal conductivities of complex oxide ceramics by doping: A case study of La₂Zr₂O₇, J. Alloys Compd., 826(2020), art. No. 154224.

[81] Liu ZG, Ouyang JH, Zhou Y, Xia XL. Effect of Ti substitution for Zr on the thermal expansion property of fluorite-type Gd₂Zr₂O₇. Mater. Des., 2009, 30(9): 3784.

[82] Wang CJ, Wang Y, Fan XZ, Huang WZ, Zou BL, Cao XQ. Preparation and thermophysical properties of La₂(Zr_0.7Ce_0.3)₂O₇ ceramic via sol–gel process. Surf. Coat. Technol., 2012, 212, 88.

[83] Wang YF, Yang F, Xiao P. Role and determining factor of substitutional defects on thermal conductivity: A study of La₂(Zr_1−xB_x)₂O₇ (B = Hf, Ce, 0 ≤ x ≤ 0.5) pyrochlore solid solutions. Acta Mater., 2014, 68, 106.

[84] Ma W, Li XY, Yin YC, et al. The mechanical and thermophysical properties of La₂(Zr_1−xCe_x)₂O₇ ceramics. J. Alloys Compd., 2016, 660, 85.

[85] Liu L, Xu Q, Wang FC, Zhang HS. Thermophysical properties of complex rare-earth zirconate ceramic for thermal barrier coatings. J. Am. Ceram. Soc., 2008, 91(7): 2398.

[86] Liu L, Wang FC, Ma Z, Xu Q, Fang SG. Thermophysical properties of (Mg_xLa_0.5−xSm_0.5)₂(Zr_0.7Ce_0.3)₂O_7−x (x = 0, 0.1, 0.2, 0.3) ceramic for thermal barrier coatings. J. Am. Ceram. Soc., 2011, 94(3): 675.

[87] Zhao M, Ren XR, Yang J, Pan W. Low thermal conductivity of rare-earth zirconate-stannate solid solutions (Yb₂Zr₂O₇)_1−x(Ln₂Sn₂O₇)_x (Ln = Nd, Sm). J. Am. Ceram. Soc., 2016, 99(1): 293.

[88] Xue ZL, Wu SQ, Qian LH, Byon E, Zhang SH. Influence of Y₂O₃ and Ta₂O₅ co-doping on microstructure and thermal conductivity of Gd₂Zr₂O₇ ceramics. J. Mater. Eng. Perform., 2020, 29(2): 1206.

[89] Guo L, Guo HB, Peng H, Gong SK. Thermophysical properties of Yb₂O₃ doped Gd₂Zr₂O₇ and thermal cycling durability of (Gd_0.9Yb_0.1)₂Zr₂O₇/YSZ thermal barrier coatings. J. Eur. Ceram. Soc., 2014, 34(5): 1255.

[90] F.F. Zhou, L.P. Xu, C.M. Deng, et al., Nanomechanical characterization of nanostructured La₂(Zr_0.75Ce_0.25)₂O₇ thermal barrier coatings by nanoindentation, Appl. Surf. Sci., 505(2020), art. No. 144585.

[91] Wang DZ, Dong SJ, Zeng JY, et al. Influence of doping Mg²⁺ or Ti⁴⁺ captions on the microstructures, thermal radiation and thermal cycling behavior of plasma-sprayed Gd₂Zr₂O₇ coatings. Ceram. Int., 2020, 46(9): 13054.

[92] Z.Y. Shen, G.X. Liu, R.D. Mu, L.M. He, Z.H. Xu, and J.W. Dai, Effects of Er stabilization on thermal property and failure behavior of Gd₂Zr₂O₇ thermal barrier coatings, Corros. Sci., 185(2021), art. No. 109418.

[93] Jiang D, Wang YF, Wang S, Liu RJ, Han J. Thermal conductivity of air plasma sprayed yttrium heavily-doped lanthanum zirconate thermal barrier coatings. Ceram. Int., 2019, 45(3): 3199.

[94] Cantor B, Chang ITH, Knight P, Vincent AJB. Microstructural development in equiatomic multicomponent alloys. Mater. Sci. Eng. A, 2004, 375–377, 213.

[95] Yeh JW, Chen SK, Lin SJ, et al. Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes. Adv. Eng. Mater., 2004, 6(5): 299.

[96] Wright AJ, Wang QY, Ko ST, Chung KM, Chen RK, Luo J. Size disorder as a descriptor for predicting reduced thermal conductivity in medium- and high-entropy pyrochlore oxides. Scripta Mater., 2020, 181, 76.

[97] Y.H. Wang, Y.J. Jin, T. Wei, et al., Size disorder: A descriptor for predicting the single- or dual-phase formation in multi-component rare earth zirconates, J. Alloys Compd., 918(2022), art. No. 165636.

[98] Yang HB, Lin GQ, Bu HP, et al. Single-phase forming ability of high-entropy ceramics from a size disorder perspective: A case study of (La_0.2Eu_0.2Gd_0.2Y_0.2Yb_0.2)₂Zr₂O₇. Ceram. Int., 2022, 48(5): 6956.

[99] Li F, Zhou L, Liu JX, Liang YC, Zhang GJ. High-entropy pyrochlores with low thermal conductivity for thermal barrier coating materials. J. Adv. Ceram., 2019, 8(4): 576.

[100] Ren K, Wang QK, Shao G, Zhao XF, Wang YG. Multicomponent high-entropy zirconates with comprehensive properties for advanced thermal barrier coating. Scripta Mater., 2020, 178, 382.

[101] Ren K, Wang QK, Cao YJ, Shao G, Wang YG. Multicomponent rare-earth cerate and zirconocerate ceramics for thermal barrier coating materials. J. Eur. Ceram. Soc., 2021, 41(2): 1720.

[102] He JJ, He G, Liu J, Tao JC. New class of high-entropy defect fluorite oxides RE2(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ (RE = Y, Ho, Er, or Yb) as promising thermal barrier coatings. J. Eur. Ceram. Soc., 2021, 41(12): 6080.

[103] D. Song, T. Song, U. Paik, et al., Glass-like thermal conductivity in mass-disordered high-entropy (Y, Yb)₂(Ti, Zr, Hf)₂O₇ for thermal barrier material, Mater. Des., 210(2021), art. No. 110059.

[104] Zhang YH, Xie M, Wang ZG, et al. Marked reduction in the thermal conductivity of (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂Zr₂O₇ high-entropy ceramics by substituting Zr⁴⁺ with Ti⁴⁺. Ceram. Int., 2022, 48(7): 9602.

[105] Luo XW, Luo LR, Zhao XF, et al. Single-phase rare-earth high-entropy zirconates with superior thermal and mechanical properties. J. Eur. Ceram. Soc., 2022, 42(5): 2391.

[106] X.W. Luo, R.Q. Huang, C.H. Xu, S. Huang, S.E. Hou, and H.Y. Jin, Designing high-entropy rare-earth zirconates with tunable thermophysical properties for thermal barrier coatings, J. Alloys Compd., 926(2022), art. No. 166714.

[107] Yan RX, Liang WP, Miao Q, et al. Mechanical, thermal and CMAS resistance properties of high-entropy (Gd_0.2Y_0.2Er_0.2Tm_0.2Yb_0.2)₂Zr₂O₇ ceramics. Ceram. Int., 2023, 49(12): 20729.

[108] Y.H. Zhang, M. Xie, Z.G. Wang, et al., Unveiling the underlying mechanism of unusual thermal conductivity behavior in multicomponent high-entropy (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂ (Zr_1−xCe_x)₂O₇ ceramics, J. Alloys Compd., 958(2023), art. No. 170471.

[109] Zhou L, Li F, Liu JX, et al. High-entropy thermal barrier coating of rare-earth zirconate: A case study on (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Zr₂O₇ prepared by atmospheric plasma spraying. J. Eur. Ceram. Soc., 2020, 40(15): 5731.

[110] Zhu JT, Meng XY, Zhang P, et al. Dual-phase rare-earth-zirconate high-entropy ceramics with glass-like thermal conductivity. J. Eur. Ceram. Soc., 2021, 41(4): 2861.

[111] Fan W, Bai Y, Liu YF, et al. Principal element design of pyrochlore-fluorite dual-phase medium- and high-entropy ceramics. J. Mater. Sci. Technol., 2022, 107, 149.

[112] Liu HL, Pang S, Liu CQ, Wu YT, Zhang GJ. High-entropy yttrium pyrochlore ceramics with glass-like thermal conductivity for thermal barrier coating application. J. Am. Ceram. Soc., 2022, 105(10): 6437.

[113] Y.L. Wang, G.Q. Lin, L.X. Yang, et al., Preparation and thermophysical properties of a novel dual-phase and single-phase rare-earth-zirconate high-entropy ceramics, J. Alloys Compd., 938(2023), art. No. 168551.

[114] Liu DB, Shi BL, Geng LY, Wang YG, Xu BS, Chen YF. High-entropy rare-earth zirconate ceramics with low thermal conductivity for advanced thermal-barrier coatings. J. Adv. Ceram., 2022, 11(6): 961.

[115] Zhao ZT, Guo RF, Mao HR, Shen P. Effect of components on the microstructures and properties of rare-earth zirconate ceramics prepared by ultrafast high-throughput sintering. J. Eur. Ceram. Soc., 2021, 41(11): 5768.

[116] K.B. Zhang, W.W. Li, J.J. Zeng, et al., Preparation of (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Zr₂O₇ high-entropy transparent ceramic using combustion synthesized nanopowder, J. Alloys Compd., 817(2020), art. No. 153328.

[117] Deng SX, He G, Yang ZC, Wang JX, Li JT, Jiang L. Calcium–magnesium–alumina–silicate (CMAS) resistant high entropy ceramic (Y_0.2Gd_0.2E_0.2Yb_0.2Lu_0.2)₂Zr₂O₇ for thermal barrier coatings. J. Mater. Sci. Technol., 2022, 107, 259.

[118] Y.H. Zhang, M. Xie, Z.G. Wang, et al., Exploring the increasing behavior of thermal conductivity for high-entropy zirconates at high temperatures, Scripta Mater., 228(2023), art. No. 115328.

[119] Y.R. Li, Q. Wu, M.L. Lai, et al., Influence of chemical disorder on mechanical and thermal properties of multi-component rare earth zirconate pyrochlores (nRE_1/n)₂Zr₂O₇, J. Appl. Phys., 132(2022), No. 7, art. No. 075108.

[120] Fan Y, Wu Q, Yao Y, Wang JM, Zhao JL, Liu B. Temperature effect on mechanical and thermal properties of multicomponent rare-earth zirconate pyrochlores. J. Am. Ceram. Soc., 2023, 106(2): 1500.

[121] Li T, Ma Z, Liu L, Zhu SZ. Thermal properties of Sm₂Zr₂O₇–NiCr₂O₄ composites. Ceram. Int., 2014, 40(7): 11423.

[122] Yang J, Wan CL, Zhao M, Shahid M, Pan W. Effective blocking of radiative thermal conductivity in La₂Zr₂O₇/LaPO₄ composites for high temperature thermal insulation applications. J. Eur. Ceram. Soc., 2016, 36(15): 3809.

[123] A. Qayyum, S. Azam, A.H. Reshak, et al., Spin-dependent first-principles study on optoelectronic properties of neodymium zirconates pyrochlores Nd₂Zr₂O₇ in Fd-3m and pmma phases, Molecules, 27(2022), No. 17, art. No. 5711.

[124] Wang L, Eldridge JI, Guo SM. Thermal radiation properties of plasma-sprayed Gd₂Zr₂O₇ thermal barrier coatings. Scripta Mater., 2013, 69(9): 674.

[125] Wang DY, Liu L, Liu YB, Li T, Ma Z, Wu HX. Heat insulating capacity of Sm₂Zr₂O₇ coating added with high absorptivity solids. Ceram. Int., 2017, 43(2): 2884.

[126] Wang YF, Xiao P. The phase stability and toughening effect of 3Y-TZP dispersed in the lanthanum zirconate ceramics. Mater. Sci. Eng. A, 2014, 604, 34.

[127] Zhong XH, Zhao HY, Liu CG, et al. Improvement in thermal shock resistance of gadolinium zirconate coating by addition of nanostructured yttria partially-stabilized zirconia. Ceram. Int., 2015, 41(6): 7318.

[128] Schmitt MP, Stokes JL, Rai AK, Schwartz AJ, Wolfe DE. Durable aluminate toughened zirconate composite thermal barrier coating (TBC) materials for high temperature operation. J. Am. Ceram. Soc., 2019, 102(8): 4781.

[129] Luo XW, Huang S, Xu CH, Hou SE, Jin HY. Rare-earth high-entropy aluminate-toughened-zirconate dual-phase composite ceramics for advanced thermal barrier coatings. Ceram. Int., 2023, 49(1): 766.

[130] Yu YC, Godbole EP, Berrios J, Hewage N, Poerschke DL. Slow sintering in garnet-containing Y and Gd zirconate–aluminate mixtures for thermal barrier coatings. J. Am. Ceram. Soc., 2023, 106(8): 4519.

[131] Carpio P, Salvador MD, Borrell A, Sánchez E. Thermal behaviour of multilayer and functionally-graded YSZ/Gd₂Zr₂O₇ coatings. Ceram. Int., 2017, 43(5): 4048.

[132] Rai AK, Schmitt MP, Dorfman MR, Zhu DM, Wolfe DE. Comparison of single-phase and two-phase composite thermal barrier coatings with equal total rare-earth content. J. Therm. Spray Technol., 2018, 27(4): 556.

[133] G. Jin, Y.C. Fang, X.F. Cui, et al., Effect of YSZ fibers and carbon nanotubes on bonding strength and thermal cycling lifetime of YSZ–La₂Zr₂O₇ thermal barrier coatings, Surf. Coat. Technol., 397(2020), art. No. 125986.

[134] Y. Liu, K.Y. Chen, A. Kumar, and P. Patnaik, Principles of machine learning and its application to thermal barrier coatings, Coatings, 13(2023), No. 7, art. No. 1140.

[135] D.D. Ye, W.Z. Wang, Z. Xu, C.D. Yin, H.T. Zhou, and Y.J. Li, Prediction of thermal barrier coatings microstructural features based on support vector machine optimized by cuckoo search algorithm, Coatings, 10(2020), No. 7, art. No. 704.

[136] H. Zhu, D.P. Li, M. Yang, and D.D. Ye, Prediction of microstructure and mechanical properties of atmospheric plasma-sprayed 8YSZ thermal barrier coatings using hybrid machine learning approaches, Coatings, 13(2023), No. 3, art. No. 602.