Lead‐free piezoceramics with the composition (1−x)(K _{1− y} N a _y )NbO ₃ ‐x(Bi _1/2 Na _1/2 )ZrO ₃ ( KN yN‐ xBNZ ) were prepared using a conventional solid‐state route. X‐ray diffraction, Raman spectroscopy, and dielectric measurements as a function of temperature indicated the coexistence of rhombohedral (R) and tetragonal (T) phase, typical of a morphotropic phase boundary ( MPB ) as the BNZ concentration increased and by adjusting the K/Na ratio. High remnant polarization ( P _r =24 μC/cm ² ), piezoelectric coefficient ( d ₃₃ =320 pC /N), effective piezocoefficient ({d_{33}^*}=420 pm/V), coupling coefficient ( k _p =48%), and high strain ( S =0.168%) were obtained at room temperature, but significant deterioration of P _r , {d_{33}^*}, and k _p were observed by increasing from room temperature to 160°C (17.5 μC/cm ² , 338 pm/V, and 32%, respectively) associated with a transition to a purely T phase. Despite these compositions showing promise for room‐temperature applications, the deterioration in properties as a function of increasing temperature poses challenges for device design and remains to be resolved.

The optical bandgap of orthorhombic ferroelectric KNbO₃ is shown to be continuously controllable via Bi and Fe co-substitution according to a K_1-xBi_xNb_1-xFe_xO₃ doping mechanism. The room temperature X-ray diffraction data combined with Raman spectroscopy analysis show the polar orthorhombic crystal structure to persist up to x = 0.25, while the bandgap narrows monotonically by 1 eV (∼33%). In-situ Raman spectroscopy corroborates the polar nature of all compositions in the temperature range of –100 to 200 °C. The ability to control the bandgap while maintaining the spontaneous polarisation makes the K_1-xBi_xNb_1-xFe_xO₃ system interesting for photoinduced processes in a wide temperature range.

Lead-free ceramics with the composition 0.91K_1/2Bi_1/2TiO₃–0.09(0.82BiFeO₃-0.15NdFeO₃-0.03Nd_2/3TiO₃) were prepared using a conventional solid state, mixed oxide route. The ceramics exhibited a high strain of 0.16% at 6 kV mm⁻¹, stable from room temperature to 175 °C, with a variation of <10%. The materials were fabricated into multilayer structures by co-firing with Pt internal electrodes. The prototype multilayer actuator exhibited constant strains up to 300 °C with a variation of ∼15%. The composition showed fatigue resistant behaviour in both monolithic and multilayer form after bipolar loading of 10⁶ cycles.