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Lead-Free KNN Piezoelectric Stack Actuators for Semi-Active Suspension Control: Correlating Fabrication, Microstructure, and Electromechanical Performance
Yan Duan
Faculty of Vehicle Engineering, Chongqing Industry Polytechnic University, Chongqing, 401120, China
received December 4, 2025, received in revised form January 6, 2026, accepted January 16, 2026
Pages 1-12 DOI: 10.4416/JCST2025-00040
Abstract
This study reports on the design, processing, and functional assessment of Li/Sb/Ta-modified (K0.5Na0.5)NbO3 ceramics targeted for environmentally compliant high-force actuators in automotive vibration management. Ten compositions were synthesized on the basis of solid-state reaction with sintering between 1 050 and 1 150 °C, and multi-scale characterization combined in situ high-temperature XRD, SEM, HRTEM, Raman spectroscopy, XPS, EBSD, BET analysis, dielectric spectroscopy, and impedance measurements with actuator-level electromechanical testing. Compositional tuning established an orthorhombic-tetragonal coexistence window in which the benchmark composition (K0.45Li0.05)(Na0.47Li0.03)(Nb0.90Sb0.06Ta0.04)O3 exhibits 58 % orthorhombic and 42 % tetragonal phases, an O-T transition at 195 °C, and a Curie point above 380 °C. At an optimized sintering temperature of 1 100 °C this ceramic reaches a density of 4.59 g/cm3 (99.2 % theoretical), grain sizes of about 2.4 μm, and a specific surface area of 1.2 m2/g, together with εr = 1 850 and tanδ ≈ 2.5 % at 1 kHz. Moderate oxygen vacancy contents around 7.5 % balance grain-boundary softening and insulation, yielding d33 = 432 pC/N, kp = 0.45, Pr = 28.7 μC/cm2, and Ec = 12.4 kV/cm. Long-term reliability is demonstrated by 94.3 % retention of d33 after 1 000 h aging at 85 °C and only 6.8 % degradation after 106 bipolar cycles at 50 Hz. Prototype 10-layer multilayer devices fabricated from the optimized composition show stable displacement response under fields of several kV/mm, confirming the potential of these lead-free ceramics for robust, RoHS-compliant smart suspension hardware. The integrated processing-structure-property correlations established here provide a transferable framework for tuning phase boundaries and defect chemistry in next-generation lead-free actuator ceramics for automotive applications.
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Keywords
Phase boundary engineering, relaxor ferroelectricity, defect-mediated conduction, multilayer ceramic devices, automotive vibration isolation
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