Chemical-Composition Tuning-Enabled Optimization of Structure, Properties, and Performance of Lead-Free (1 – x)BaZr_0.05Ti_0.95O₃–(x)Ba_0.92Ca_0.08TiO₃ Electroceramics

Abstract

Barium titanate (BaTiO 3 ) and its derivatives, which belong to the family of perovskite oxides, offer a class of lead (Pb)free ferroelectric and piezoelectric materials with numerous applications in electronic and electromagnetic devices. In this study, we report on the Pb-free materials with a variable composition (1 − x)BZT5−(x)BCT8 (x = 0.00−1.00) where BZT5 refers to BaZr 0.05 Ti 0.95 O 3 and BCT8 refers to Ba 0.92 Ca 0.08 TiO 3 . The substitution of Zr 4+ for Ti 4+ and Ca 2+ for Ba 2+ in the BaTiO 3 matrix enhances the properties and performance desirable for applications involving ferroelectric capacitors and memory storage devices. X-ray diffraction (XRD) studies coupled with Rietveld refinement analyses confirm the biphasic (major tetragonal and minor orthorhombic) crystal structure of all the samples. Raman spectroscopic studies corroborate with XRD results and validate the biphasic crystal structure. Chemically homogeneous samples exhibit the characteristic granular-dense microstructure. The density measurements using Archimedes' principle indicate that the sample density is above 5.31 g/cm 3 (90%). Ferroelectric measurements display typical polarization-electric field (P−E) hysteresis, confirming the ferroelectric nature and electric field-induced strain butterfly (S−E) loops, confirming the piezoelectric nature of all the samples. The dielectric properties of all of the compositions indicate significant prospects for future capacitor applications. Ferroelectric measurements show that BZT5 exhibits a maximum value of 0.70 squareness ratio, indicating that BZT5 can be a suitable material for permanent ferroelectric random-access memory (Fe-RAM) applications, whereas 0.75BZT5−0.25BCT8 is suitable for switching applications. The moderately higher remnant polarization (P r = 11.22 μC/cm 2 ) and the lower coercive field (E c = 2.54 kV/cm) are obtained for BCT8. The piezoelectric coefficient and strain studies show that sample with x = 0.50 exhibits a higher converse piezoelectric coefficient of 430 ± 1 pm/V and 0.179 (% strain). The Q-factor for the BZT5 composition was observed to be 4.13 × 10 −4 (cm 2 /μC) 2 , which is the maximum among the studied compositions, suggesting that BZT5 may be a suitable candidate for energy conversion transducer applications.