Influence of Ti-vacancies on the site occupancy of amphoteric calcium, oxygen vacancies, dielectric, optical, and ferroelectric behavior of Ba0.8Ca0.2Ti1-O3-δ

Abstract

The defect chemistry of the amphoteric Ca2+ dopant in BaTiO3 is a controversial issue, particularlyregarding its site occupancy, solubility limit, and impact on material properties due to the chargecompensation mechanism involved. In the present research work, the effect of intentionallyproduced Ti4+ vacancies was investigated on the structure and properties of Ba0.8Ca0.2Ti1-xO3- (x= 0.005, 0.01, 0.03, 0.05). A phase transition from ferro- to para-electric phase was observed withan increase in x. Raman spectroscopy revealed that Ca2+ also occupies the BO6 octahedron bymoving from A- to B-site. However, still oxygen vacancies (VO∙∙exist due to lower oxidation of Ca2+ han Ti4+ supported by electron paramagnetic spectroscopy which revealed a signal at 2.004, associated with Ti deficiency, producing VO ∙∙ The grain growth was also inhibited (decreased from11.4 m to 1.36 m) by the generation of vacancies which decreased the value of r from 8085 to 1405 at Tc. These defects were also evident from the P-E loops which exhibited double hysteresis- like behavior, associated with defects in the material. The formation of VO ∙∙ also greatly affected the optical band gap due to an increase in distortion in the structure. The band gap increased from 2.64 to 2.74 eV with an increase in x from 0.005 to 0.03. It was found that Ca2+ plays a vital role by shifting to B-site to reduce Ti-vacancies which affected the structure and properties of the Ba0.8Ca0.2TiO3. The sample with the highest symmetry (x = 0.05) shows a slim double hysteresis loop and a remnant polarization of 0.85 μC/cm2 at 50 kV/cm, which indicates its potential for use in high energy density applications.