Phonon dynamics in lead free perovskite (1-x)KNN-xBAN (x = 0.0–0.1): a temperature dependent raman study

Abstract

K0.5Na0.5NbO3 (KNN) has been under extensive focus in recent times due to it being an alternative to lead-free multifunctional materials and properties like room temperature ferroelectricity, stability in air and technology friendly applications. In this work, we report a comprehensive temperature dependent, compositional change induced structural variation and polarization dependent Raman spectroscopy on BaAl0.5Nb0.5O3 (BAN) doped KNN in the spectral range of 10–1000 cm−1. Multiple phase transitions are marked by the strong renormalization of the phonon self-energy parameters, i.e. mode frequencies and linewidths, in the temperature range of 83 K to 623 K. Change in the phase transition temperature is tracked via phonon anomalies with varying doping concentration, x = 0.0, 0.02, 0.05, 0.07 and 0.1, and is found to be as large as ∼100 K for orthorhombic to tetragonal phase transition for x = 0.1. Raman extracted phase diagram shows that the stability of the ferroelectric orthorhombic phase in the vicinity of room temperature increases with the increasing doping concentration. Also, from our polarization-dependent measurements we could decipher the symmetry of the observed phonon modes for KNN system.