Structural, optical, and electrical properties of vanadium-doped, lead-free BCZT ceramics

Abstract

In this paper, we report the synthesis of vanadium (V)-doped Ba0.9Ca0.1Ti0.9−xVxZr0.1O3 (BCZT) ceramic oxides prepared using conventional solid-state reaction methods. The X-ray diffraction (XRD) pattern confirmed the formation of the tetragonal phase—with the space group P4mm—in all samples. A barium vanadate (Ba3V2O8) impurity phase was observed in the doped samples, which suggests that the solubility limit of V was reached in the BCZT ceramics. X-ray photoelectron spectroscopy shows the formation of oxygen vacancies, which attain a maximum value at a concentration x = 0.02, i.e., 38.65%. Fourier-transform infrared analysis shows prominent peaks between 560 cm−1 to 558.1 cm−1, with a secondary-phase peak around 1017 ± 2 cm−1, as suggested by XRD. Photoluminescence (PL) spectra suggest that oxygen vacancies play important roles in promoting luminescence by trapping the excited photoelectrons. Oxygen vacancies also reduce the recombination rate of photo-generated electrons and holes. Ultraviolet–visible analysis agreed with PL studies, with comparable bandgap energy. Raman spectroscopy also shows the tetragonal phase, with the most-prominent peak around 520 cm−1 due to the A1(TO3)/E(TO) mode. We attribute two peaks observed around 330 cm−1 and 780 cm−1 to the Eg and A1g modes, respectively, of the secondary phase. Electrical studies performed for all samples reveal that variable oxidation states of Vin the presence of oxygen vacancies readily influence the resistivity—and thus the activation energy—of each sample. We obtained a maximum DC resistivity ρDC (max.) = 1.653 × 10−11(Ω cm) and a corresponding minimum DC conductivity σDC (min.) = 8.581 × 10−12 for x = 0.02, which is due to the presence of only an acceptor (V3+) concentration for this sample. The Curie temperature (Tc) also decreased from 71.8 °C to 31 °C with increasing V-ion concentration. The drift mobilities observed for all samples are in accordance with the Verwey–de Boer mechanism. Thus, the substitution of V ions at Ti sites can significantly influence the optical and electrical properties of BCZT ceramics.