Ferroelastic structure AlNb _1/2 Ta _1/2 O ₄ ceramics with improved thermophysical and mechanical properties

Abstract Effect of B site doping on structural, thermophysical, and mechanical properties of AlNb _x Ta _1‐x O ₄ ceramics obtained by solid‐phase sintering were investigated in this work. Ferroelastic domain structures derived from the reversible second‐order ferroelastic transformation between the tetragonal (t) and monoclinic (m) contribute to improving the high‐temperature fracture toughness of AlNb _x Ta _1‐x O ₄ ceramics, and the room fracture toughness of AlNb _1/2 Ta _1/2 O ₄ ceramics is 3.4 MPa·m ^0.5 . The brittleness index of AlNb _1/2 Ta _1/2 O ₄ (2.6 μm ^−0.5 ) is also lower than AlTaO ₄ , which indicates that has better damage tolerance. Compared with single‐component AlTaO ₄ and AlNbO ₄ , the AlNb _1/2 Ta _1/2 O ₄ has a lower thermal conductivity due to enhanced phonon scattering caused by mass disorder and lattice distortion effects. Additionally, AlNb _1/2 Ta _1/2 O ₄ has a good match with the coefficient of thermal expansion of ceramic matrix composites (CMCs), and hence, AlNb _1/2 Ta _1/2 O ₄ has a considerable potential to be the candidate material for thermal/environmental barrier coatings (T/EBCs).