Optimal Nb5+ doping for enhanced optical reflectivity and improved thermophysical properties of La0.9Sr0.1Ti1?xNbxO3+δ

Thermal protection materials with high optical reflectivity, low thermal conductivity, and good high-temperature stability are required for the development of laser technologies and the protection of the critical equipment components. Herein, we synthesize a novel thermal protective material, La_0.9Sr_0.1Ti_1?xNb_xO_3+δ (LSTN; x = 0.1, 0.125, 0.15), with different Nb⁵⁺-ion contents using solid-state sintering. Phase structure analysis demonstrates that LSTN (x = 0.1, 0.125, 0.15) presents a single-phase monoclinic structure with a uniform element distribution. In particular, the LSTN_0.125 ceramic exhibits ultrahigh optical reflectivity (96%, 2300 nm) and excellent thermophysical properties, such as a high thermal expansion coefficient (10.3 × 10^?6 K^?1, 1000°C), an ultralow thermal conductivity (0.408 W (m K)^?1, 300°C), and excellent high-temperature stability. Aberration-corrected scanning transmission electron microscopy reveals that the disordered substitution of Nb⁵⁺ ions induces numerous lattice distortions and mass fluctuations, which decrease the thermal conductivity, and makes difference in the relative refractive indices of atomic layers causing the high reflectivity of the material. These remarkable properties render the LSTN_0.125 ceramic as an ideal alternative for near-infrared thermal protection applications.