Synthesis and conductivity properties of Gd0.8Ca0.2BaCo2O5+δ double perovskite by sol–gel combustion

Abstract

Double perovskite oxides Gd 0.8 Ca 0.2 BaCo 2-O 5?d have been successfully prepared by EDTA-citrate complexation process. The prepared samples were characterized by means of thermogravimetry-differential analysis, X-ray diffraction, Fourier transform infrared spectroscopy techniques. These analyses suggested that pure Gd 0.8 Ca 0.2 BaCo 2 O 5?d phase could be formed when the pH value was maintained above three and calcination temperature was higher than 850°C. The conductivity properties analyzed by means of four probes method, scanning electron microscopy and X-ray photoelectron spectroscopy indicated an improvement in conductivity with a high value of nearly 1200 S/cm, which was due to an increase in the number of small polaron hopping conduction units, Co 3? -O-Co 4? . Interestingly, the Gd 0.8-Ca 0.2 BaCo 2 O 5?d samples exhibited a semiconducting behavior through a wide range of temperature below 100°C and a metallic behavior at 100-500°C, thereby demonstrating that Gd 0.8 Ca 0.2 BaCo 2 O 5?d could meet the requirements of a smart material.

Enhancing the Thermoelectric Performance of Calcium Cobaltite Ceramics by Tuning Composition and Processing

“…The Co 2p 3/2 spectra are deconvoluted into three peaks, where the first peak at 779.26–779.30 eV corresponds to Co 3+ , the second peak at 780.26–780.30 eV is assigned to Co 2+ , and the third at 782.06–782.10 eV is ascribed to Co 4+ . These results are consistent with published Co 2p XPS data − and confirm a mixture of valence for cobalt in the calcium cobaltite lattice. The fractions for each cobalt species (obtained from Figure and Figure S6) are presented in Table .…”

Hollow Co‐Based Layered Double Hydroxide Decorated with Ag Nanoparticles for the Oxygen Evolution Reaction

“…at 786.74 eV and 802.48 eV (Figure 1C), suggesting the co-existence of Co 2 + and Co 3 + in HÀ CoÀ LDH. [23] While the high-resolution for Co 2p spectrum of Ag@CoÀ LDH indicates the existence of Co 4 + (782.92 eV and 798.72 eV) besides Co 2 + (781.12 eV and 797.19 eV) and Co 3 + (780.32 eV and 780.32 eV), [24] suggesting the presence of higher valent of Co species. According to previous reports, these higher oxidation states of Co are known to be robust active sites for water oxidation.…”

Electrochemically Controlled Switchable Copolymerization of Lactide, Carbon Dioxide, and Epoxides

“…The CV showed the reversible redox process of the interconversion between Co III –Mn III and Co II –Mn II [34] . XPS was also used to study the chemical states and surface compositions of Cat.1 before and after electrolysis, revealing that no other valence states were obtained (Figure S3) [35] …”