Structural and spectroscopic properties of Yb/Nd doped K0.5Na0.5NbO3 lead-free ferroelectric ceramics

Neodymium and ytterbium-co-doped potassium sodium niobate (KNN) meso-sized particles, were prepared using the optimized Pechini process. The prepared gels underwent thorough characterization using differential scanning calorimetry with thermogravimetry coupled with evolve gas analysis, whereas the obtained powders were studied by means of X-ray diffraction, scanning electron microscopy. The calcination and sintering temperatures were chosen based on DSC/TG analysis and dilatometry studies, respectively. XRD patterns confirmed only orthorhombic KNN phase formation (Amm2). Incorporating Nd3 + and Yb3+ ions led to changes in lattice parameters and crystallite size (82.66-129.99 nm) of both powders and sinters. Sinters indicated dielectric behavior, with activation energy ranging between 2.89 and 3.02 eV. Three luminescence bands in the range of 800-1100 nm were observed in photoluminescence spectra, after excitation from 700 to 840 nm. Moreover, strong green light up-conversion emission was observed and described. Dielectric and piezoelectric properties investigated by electrochemical impedance spectroscopy showed that introducing Yb3+ and Nd3+ cations into potassium sodium niobate significantly influenced its parameters.