Effect of Crystal Structure and Phase on the Dielectric, Ferroelectric, and Piezoelectric Properties of Ca2+- and Zr4+-Substituted Barium Titanate

Abstract

Barium titanate (BaTiO3) and its associate ternary metal oxide systems constitute versatile materials with immense potential for various technological applications in electronics and optoelectronics. Herein, we report on the synthesis and property optimization of lead-free ceramic samples, namely BaTiO3 (BT), BaZr0.2Ti0.8O3 (BZT), Ba0.7Ca0.3TiO3 (BCT), and BaZr0.2Ti0.8O3–0.5 Ba0.7Ca0.3TiO3 (BZT–BCT) composites. All of these materials were synthesized by the standard solid-state chemical reaction method, where tuning the composition and the crystal structure yields materials suitable for multifaceted applications related to capacitors, memory storage, and high-energy switching and transducers. Structural studies carried out using X-ray diffraction and Raman spectroscopy confirm the tetragonal phase for BT, BZT, and BZT–BCT samples, whereas BCT is a biphasic crystal system, which contains a small amount of the CaTiO3 phase. Scanning electron microscopy characterization of the surface morphology indicates the granular-dense microstructures of all of the samples. Energy dispersive spectroscopy confirms the high degree of purity and chemical homogeneity of the synthesized samples in addition to a well-maintained composition. Density measurements using Archimedes principles show that all of the samples have densities above 4.96 g/cm3. All of these materials exhibit typical polarization–electric field (P–E) hysteresis and field-induced strain butterfly (S–E) loops, which confirm their ferroelectric and piezoelectric nature. The frequency response of the dielectric constant shows a maximum dielectric constant of 2441 for pure BT and it decreases for higher frequencies, above 0.1 MHz. The dielectric properties of BT imply significant prospects for its future capacitor applications. Ferroelectric measurements, which are established by measuring the P–E hysteresis loop at 300 K, show that the BCT samples exhibit a 0.50 squareness ratio. The detailed analyses indicate that BCT is a candidate material for permanent memory storage device (FeRAM) applications, whereas BZT is good for switching applications. Furthermore, a moderately higher remnant polarization (Pr = 10.81 μC/cm2) is obtained for BT and a lower coercive field (Ec = 0.78 kV/cm) is obtained for the BZT sample. Also, piezoelectric coefficient and strain measurements show that BT has a piezoelectric coefficient of 183 ± 1 pC/N and a converse piezoelectric coefficient of 365.7 ± 2 pm/V, which are the highest values. The Q-factor for the BZT–BCT composite was observed to be 4.16 × 10–4 (cm2/μC)2, which is maximum, implying that BZT–BCT is suitable for energy conversion transducer applications. In this work, we comprehensively elucidate and discuss the properties and potential applications of BT and its associated ternary metal oxide systems.