High-temperature and long-term stability of Ho-doped potassium sodium niobate-based multifunctional ceramics

In this study, we synthesized lead-free 0.975(K0.4Na0.6)0.985Li0.015(Nb0.94Sb0.06)O3- 0.025 (Bi1-xHox)0.5Na0.5ZrO3 (KNLNS- 2.5Bi1-xHoxNZ) ceramics with excellent temperature stability and temperature-independent fatigue-free behavior. The doping with Ho3+ ions induced the phase transition from the coexisting orthorhombic (O) - tetragonal (T) crystal phase into pure T symmetry, increasing the T:O ratio. The large-signal piezoelectric constant, d33*, of the synthesized KNLNS- 2.5Bi1-xHoxNZ ceramics is almost constant in the temperature range from 30 to 120 ?C. In-situ dielectric permittivity measurement indicated that the O - T phase transition becomes more diffuse in the electrical field, contributing to improved thermal stability. Furthermore, the Ho-doped ceramics exhibited a fatigue-free behavior regardless of the temperature, rendering these materials promising for actuator applications. Besides, the Ho-modified ceramics showed excellent photoluminescence (PL) properties with strong green light emission upon 453 nm visible light excitation. Polarization- and temperature-induced PL quenching behaviors were observed. These changes may originate from the electric field- or temperature-induced phase transitions from the mixed O - T to pure T crystal symmetry. These excellent and reliable electrical and photoluminescent properties reflect the great potential of the synthesized ceramics for applications in multifunctional devices.