Enhanced electrical properties of lead-free sodium potassium niobate piezoelectric ceramics prepared via cold sintering assisted sintering†

Abstract

It is a great challenge to prepare dense (K,Na)NbO₃ (KNN)-based ceramics with low volatilization of K⁺/Na⁺ ions utilizing a conventional solid state reaction method. Herein, ternary KNNS–BNZS–BZ ceramics were prepared utilizing the conventional solid state reaction sintering (CS) method and the cold sintering-assisted sintering (CSAS) process. The CSAS process was used to prepare discs using KMnO₄ solution as a transient melt and held at 225 °C under a uniaxial pressure of 380 MPa for 30 min. The microstructures and piezoelectric properties of the prepared ceramics were investigated. The density and piezoelectric performances of the ceramics prepared via CSAS are much superior to those of the counterparts by the conventional solid-state reaction. The piezoelectric constant d₃₃ of the CSAS ceramic with strong ferroelectric properties reaches a high value of ∼470 pC N⁻¹. The XRD Rietveld refinement, dielectric–temperature curves and TEM show that the prepared KNNS–BNZS–BZ ceramics have a state of three-phase rhombohedral–orthorhombic–tetragonal (R–O–T) coexistence at room temperature. The enhanced piezoelectric properties of the CSAS ceramics are ascribed to the improved densification and reduced volatilization of K⁺/Na⁺ ions by the strategy of CSAS. The present investigation shows that the CSAS method is a potential route for the preparation of KNN-based ceramics.