Sm^(3+)substitution-mediated oxygen vacancy clustering:Theoretical analysis and experimental verification for suppressing low-temperature contraction of La_(2)Ce_(2)O_(7)ceramicsOA

Lanthanum cerate(La_(2)Ce_(2)O_(7),LC)is a promising thermal barrier coating(TBC)candidate with superior thermophysical properties over yttria-stabilized zirconia(YSZ),but its practical application is hindered by low-temperature thermal expansion coefficient(TEC)contraction.Previous studies primarily focused on regulating the oxygen vacancy concentration while neglecting the influences of vacancy distribution.Herein,we employ Sm^(3+)isovalent substitution for La^(3+)to maintain a constant vacancy concentration and isolate the vacancy distribution effects.The optimal composition(La_(0.8)Sm_(0.2))_(2)Ce_(2)O_(7)significantly suppresses low-temperature contraction,reducing the linear shrinkage rate by~88.5%and increasing the TEC by~12.56%(to 12.37×10^(-6)K^(-1))compared with LC(10.99×10^(-6)K^(-1)).Combining density functional theory(DFT)calculations and HR-TEM/AC-STEM characterization,we directly reveal Sm^(3+)-induced oxygen vacancy clustering in LC-based ceramics.The underlying mechanism involves(i)randomly distributed free vacancies inducing contraction via vacancy-phonon coupling and local symmetry breaking;(ii)Sm^(3+)substitution introducing dislocations whose stress fields,together with Sm^(3+)’s higher ionic potential,drive vacancy clustering;(iii)clustering reducing mobile vacancies and restoring lattice order,thereby suppressing contraction.This work confirms that LC''s low-temperature contraction is coregulated by vacancy concentration and distribution,complementing existing concentration-modulation strategies.