Investigation of electrical properties of perovskite-type metal oxides

Abstract

Materials development has led to the growth of several technologies to reduce carbon footprints and to develop a sustainable environment. These strategies have led to the advancement of several renewable energy storage and conversion systems like fuel cells, batteries, solar cells, and capacitors that have been beneficial and environmentally benign. Moving towards clean energy includes using renewable energy sources and safe and sustainable materials for energy applications. However, the existing issues with materials development are the use of expensive and scarcely available raw materials, complex and multiple steps in material processing, and not exploring new family of materials. This thesis addresses the use of studying the electrical properties of a family of materials known as perovskite-type oxides. The thesis focuses on the solid-state synthesis of transition metal doped double perovskite-type Ba2Ca0.67Nb1.33-xCuxO6-δ (x = 0, 0.05, 0.13 and 0.26) Ba2Ca0.67-xCuxNb1.33O6-δ (x = 0 and 0.13) and BaY0.5Nb0.5O3 (BYN). The study includes the morphology of these materials, investigation of the electrical and dielectric properties of the above materials in different atmospheres, and their chemical stability in CO2 and moisture containing environments. Among the compositions studied, Ba2Ca0.67Nb1.2Cu0.13O6-δ shows the highest conductivity of 4.6 × 10-4 Scm-1 in dry air at 600 ˚C. The dielectric studies were also conducted among the investigated samples, the highest dielectric constant exhibited by Ba2Ca0.67Nb1.2Cu0.13O6-δ (x = 0.13) was 587 and dielectric loss of 2 at 106 Hz at 500 ˚C in air. In general, Ba2Ca0.67Nb1.2Cu0.13O6-δ (x = 0.13) shows highest dielectric constant values in the range of ~100 – 600 and lowest dielectric loss exhibited by Ba2Ca0.67Nb1.28Cu0.05O6-δ (x = 0.05) was ~0.3 – 0.6 at 500 ˚C in various atmospheres. The second part of the thesis focuses on the synthesis of multi-element doped BaY0.5Nb0.5O3 (BYN) perovskite oxides, where alkaline earth and rare earth elements were doped in the A- and B-site of BYN. Synthesis and structural optimizations were also carried out to come up with pure single-phase materials. Out of all the compositions synthesized, (Ba1-xA’x)(Y1/2Nb1/2-y-zM’yM”z)O3-δ (A’ = Sr, Ca; M’ = Mg and M” = Ni) (x = 0, 0.5; y = 0, 0.1; z = 0, 0.05, 0.1), the PXRD pattern reveals the crystallization of only BaY0.5Nb0.5O3 and Ba0.5Sr0.5Y0.5Nb0.4Mg0.1O3-δ in a cubic crystal system with Pm3̅m space group. Although, the crystal formation was successful for these compositions, several attempts were made to modify and optimize the synthesis and sintering conditions. The surface morphology of the pellet samples shows BaY0.5Nb0.5O3 containing more pores and grain boundaries than that of Ba0.5Sr0.5Y0.5Nb0.4Mg0.1O3-δ, emphasizing better particles formed in doped BYN. The chemical stability of these compositions in CO2- and moisture-containing environment shows their potential to be used in devices for energy applications that are present in such operating conditions.