Rational composition design of sesquioxide (Y,Sc,Lu)2O3 single-crystal fibers for robust and high-sensitivity ultrasonic temperature sensing beyond 2100 °C

Abstract

Extreme-environment temperature sensing above 2000 °C represents a critical technological challenge for next-generation nuclear reactors, hypersonic propulsion systems, and deep-earth energy extraction. This study pioneers the development of novel mixed sesquioxide (Y_xSc_1−x)₂O₃ single-crystal fibers (SCFs) with ultra-high melting points via the micro-pulling down method (μ-PD), establishing an innovative acoustic waveguide platform for ultrasonic temperature sensors (UTSs). The lattice component variations exhibit a remarkable influence on the acoustic properties and the temperature sensing performance. The Y³⁺-rich (Y_0.6Sc_0.4)₂O₃ SCF features a lower elastic modulus and higher density compared to (Y_xSc_1−x)₂O₃ with a lower Y³⁺ concentration, which leads to a decreased acoustic velocity and a greater velocity variation, dramatically increasing the thermometry sensitivity. Subsequent investigations reveal that Lu³⁺ doping in the (Y_0.6Sc_0.4)₂O₃ SCF amplifies lattice disorder, yielding superior acoustic characteristics and enhanced unit sensitivity. Specifically, the optimized 10% Lu³⁺:(Y_0.6Sc_0.4)₂O₃ SCF-UTS demonstrates exceptional temperature sensing capabilities in the range of 25–2100 °C with a maximum unit sensitivity of 108.67 ns °C⁻¹ m⁻¹ achieved at 2100 °C, representing the highest working temperature among the contact fiber sensors and the highest unit sensitivity of the crystal-based UTSs reported to date. This work proposes a feasible strategy to improve ultrasonic thermometry performance through rational component design, providing promising candidates for high-temperature sensing towards extreme environments.