Novel X7R BaTiO3 ceramics co-doped with La3+ and Ca2+ ions

Abstract

• Structural and dielectric properties of (Ba 1−x La x )(Ti 1−x/2 Ca x/2 )O 3 were studied. • A pseudo-cubic ceramic with x = 0.03 is a novel dielectric for X7R applications. • A symmetric (2 0 0) XRD peak and sharp Raman band are characteristics of pseudo-cubic. • The unit cell volume ( V 0 ) of BLTC increases linearly with x , satisfying Vegard’s law. • Formation of defect complexes with much larger Ti-site Ca 2+ is responsible for X7R. (Ba 1− x La x )(Ti 1− x /2 Ca x /2 )O 3 (0.03 ⩽ x ⩽ 0.06) (BLTC) ceramics were prepared using a mixed oxides method. The structure, microstructure, and dielectric properties of BLTC were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscope, and dielectric measurements. Both symmetric (2 0 0) XRD peak indicative of cubicity and sharp 308 cm −1 Raman band indicative of tetragonality are characteristics of pseudo-cubic symmetry of BLTC. The unit cell volume of BLTC increased linearly with x , satisfying Vegard’s law. A strong “Raman charge effect” appeared at 836 cm −1 because of the aliovalent double substitution in BLTC. The x = 0.03 sample because of its higher permittivity ( ε ′ = ∼2000) and lower loss (tan δ < 0.04) is a novel dielectric for X7R applications. The formation of La Ba - Ca Ti ″ - La Ba defect complexes was responsible for the dielectric-temperature stability of BLTC.