Li/Mn Co-doped KBT Ceramics for High-Temperature Ultrasonic Transducers

What is it about?

With the growing demand for sensing and monitoring technologies in extreme environments such as aerospace systems and deep-well drilling, the development of high-temperature piezoelectric ceramics with high Curie temperature (TC) and strong piezoelectric activity (d33) has become an urgent challenge in the field of functional materials. Conventional lead-based piezoelectric ceramics are difficult to meet the requirements of high-temperature operation due to their relatively low Curie temperatures and environmental concerns. To address this issue, Prof. Chen Yu’s team from the School of Mechanical Engineering at Chengdu University achieved a synergistic enhancement in d33, TC, and kp through Li/Mn co-doping. The optimized composition, KBT–LM55, exhibited a d33 of 30 pC/N, an increased TC of 590 °C, and a kp of 6.4%, while retaining approximately 80% of its initial d33 after annealing at 500 °C for 4 h. Furthermore, high-temperature ultrasonic transducer verification was successfully conducted, demonstrating promising application potential.

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Photo by Jay Zhang on Unsplash

Photo by Jay Zhang on Unsplash

Why is it important?

(1) A Li/Mn co-doping strategy was proposed to synergistically optimize the crystal structure and electrical properties of KBT. After the co-substitution of Li/Mn for K/Bi sites, the KBT main phase was not only stabilized, but the content of the secondary phase Bi₁.₇₄Ti₂O₆.₆₂₄ was also effectively reduced. Meanwhile, the lattice anisotropy, TiO₆ octahedral distortion, and interlayer coupling were regulated, thereby providing a structural foundation for performance enhancement. (2) A balanced regulation between leakage suppression and polarization response was achieved while maintaining domain-wall mobility. Li/Mn doping transformed the dielectric behavior of KBT from a sharp λ-type phase transition to a diffuse or relaxor-like response, while effectively suppressing high-temperature leakage conduction and improving insulating properties. This regulation did not simply sacrifice polarization capability; rather, it enabled a balance between conductive loss suppression and domain-wall motion through defect-chemistry modulation. (3) The optimized composition KBT–LM55 was obtained and further validated in a high-temperature ultrasonic transducer. KBT–LM55 exhibited the best overall performance, with a d₃₃ of 30 pC/N, kp of 6.4%, TC of 590 °C, and a room-temperature tanδ as low as 0.23%. After annealing at 500 °C for 4 h, approximately 80% of the initial d₃₃ was retained, and resonance measurements showed that kp remained stable up to 325 °C. Furthermore, a pulse–echo ultrasonic transducer fabricated based on this material maintained stable signals at 250 °C, with a center frequency of 2.24 MHz, a −6 dB bandwidth of 33.95%, and a peak-to-peak voltage (Vp-p) of 1.94 V.

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