Microstructure, Dielectric and Piezoelectric Properties of Cold Sintered Lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramic

Abstract

Piezoelectric ceramics are widely used as actuator, resonator, spark igniter and energy harvesting applications. Lead-free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) piezoelectric have garnered immense interest due to their excellent dielectric and piezoelectric properties. However, the conventional sintering process for BCZT requires a high temperature of ~ 1500oC, which results in significant energy consumption. Recently, the cold sintering process (CSP) has emerged as a promising alternative, enabling the densification of ceramics at significantly reduced temperatures. However, there are no reports available on the cold sintering of BCZT ceramics. This study aims to investigate the factors affecting the cold sintering process of BCZT lead-free piezoelectric ceramics, focusing on flux concentration, dwell time, and sintering temperature. Here, Ba(OH)2 8H2O flux was used as a transient liquid phase and found that a concentration of 20 wt% provided the highest density, achieving a relative density of 86%. Furthermore, the sintering temperature and dwell time variation were also studied, and it was found that the effective sintering temperature was 250°C, and the dwell time was 1 hour. To further improve the density of the samples, annealing was performed at 1000°C and 1100°C, achieving a relative density of 90%. The dielectric behaviour with temperature of the cold-sintered and post-annealed BCZT samples was also characterized, revealing a dielectric constant in the cold-sintered ceramics without noticeable dielectric anomalies that generally marks the ferroelectric to paraelectric transition. After annealing, a hump indicating the Curie transition of BCZT became apparent, evolving into a broad transition peak around 90oC for annealed sample. Moreover, the annealed samples showed well-defined ferroelectric hysteresis loops, having a remanent polarization of 3.1 µC/cm2 and d33 value of 127 pC/N.