Effect of Lanthanum and Phosphate Ester Addition on Densification and Dielectric Properties of (Ca, Zr) Modified Barium Titanate

Abstract

Ferroelectric materials are used in many applications, such as capacitor, sensors, actuators and transducers. Generally, lead based materials (PZT, PMN) have dominated in piezoelectric market because of their excellent dielectric, piezoelectric properties and flexibility in terms of compositional modifications. However, due to toxicity and environmental concerns, PZT is facing global restrictions in its usage in electronic equipment. Till date the properties of developed lead free piezoelectric are not comparable to that of PZT based compositions. The breakthrough made by Liu and Ren et al. in BaTiO3-based ceramics with co-dopants of Zr, and Ca (BCZT) has offered a significant impact on the development of lead-free piezo ceramics. It featured piezoelectric constants on the order of 560–620 pm/V, clearly exceeding values for competing lead-free compositions and even those for most PZT materials.
Multilayered structure (alternate layers of piezoelectric wafers and electrodes) is preferred in most of the capacitor/actuator applications so that excitation can be done at a low voltage. The applications in structural health monitoring (SHM) often involve piezoelectric ceramics in form of wafers/substrates that are mainly produced from tape casting. Success in tape casting with the required reproducibility and consistency depends upon the degree of dispersion. Phosphate ester is a common dispersant used in non–aqueous tape casting of ceramics. However, residual phosphorous may influence densification and final electrical properties. It is worth to study the effect of phosphate ester addition on densification and electrical properties of BCZT ceramics.
Doping is a common strategy to alter the sensitivity of a material to external stimuli and optimize it for specific applications. Only limited research exists on the effect of aliovalent doping on BCZT. Typical aliovalent dopants in PZT are La3+ and Nb5+ acting as donor which significantly alter the electrical property of the final ceramics. However, the influence of La3+ additives on BCZT is not yet investigated. The present thesis also studied the effect of La3+ substitution in A-site of BCZT on densification and electrical properties of the same.
It is observed that the phosphate ester addition reduces sinterability and degrades the dielectric property of the BCZT ceramics. In case of La3+ substitution, enhances sinterability and significantly modifies the dielectric property. Impedance spectroscopy is used to explain the electrical inhomogeneity of the BCZT samples.