Influence of Ln ³⁺ and B ³⁺ Ions Co‐Substitution on Thermophysical Properties of LnMB ₁₁ O ₁₉ ‐type Magnetoplumbite LaMgAl ₁₁ O ₁₉ for Advanced Thermal Barrier Coatings

Lanthanum hexaaluminate is a promising competitor to establish yttria partially stabilized zirconia as a thermal barrier coating material for Ni ‐based superalloy due to its relative low intrinsic thermal conductivity and low sinterability at temperatures exceeding 1100°C. Sr ²⁺ and Ti ⁴⁺ were selected as two dopants to partially substitute the La ³⁺ and Al ³⁺ in LaMgAl ₁₁ O ₁₉ , respectively. The variation in thermal conductivity with Sr ²⁺ and Ti ⁴⁺ fractions was analyzed based on structure information provided by X‐ray diffraction and Raman spectroscopy. The average crystal size of LaMgAl ₁₁ O ₁₉ sintered at 1600°C for 10 min by spark plasma sintering is in nanoscale. The fully dense La _{1− x} Sr _x MgAl _{11− x} Ti _x O ₁₉ solid solution showed a minimum thermal conductivity value (λ = 1.12 W/(m K) ⁻¹ , T = 1273 K) at the composition of La _0.5 Sr _0.5 MgAl _10.5 Ti _0.5 O ₁₉ ,which possibly reduces from the enhanced phonon scattering due to mass and strain fluctuations at the Ln ³⁺ and B ³⁺ sites.