Comparative study of 2mol% Li- and Mn-substituted lead-free potassium sodium niobate ceramics

Abstract

The effect of Li and Mn substitution on the dielectric, ferroelectric and piezoelectric properties of lead free K0.5Na0.5NbO3 (KNN) was investigated. Samples were prepared using a conventional solid state reaction method. The sintering temperature for all the samples was 1050°C. The optimum doping concentration for the enhancement of different properties without the introduction of any other co-dopants such as Ti, Sb, and La was investigated. X-ray diffraction analysis confirmed that all the samples crystallize in a single phase perovskite structure. The dielectric properties were investigated as a function of temperature and applied electric field frequency. Compared with Li-substituted KNN (KLNN), Mn-substituted KNN (KMNN) exhibited a higher dielectric constant ɛ max (i.e., 4840) at its critical transition temperature T c (i.e., 421°C) along with a lower value of tangent loss at 10 kHz and greater values of saturation polarisation P s (i.e., 20.14 μC/cm2) and remnant polarisation P r (i.e., 15.48 μC/cm2). The piezoelectric constant (d 33) of KMNN was 178 pC/N, which is comparable to that of lead-based hard ceramics. The results presented herein suggest that B-site or Mn substitution at the optimum concentration results in good enhancement of different properties required for materials used in memory devices and other applications.