Oxygen deficient perovskites: effect of structure on electrical conductivity, magnetism and electrocatalytic activity.

Abstract

Oxygen evolution reaction …………………………………………....19 CHAPTER 2. TRANSFORMATION OF STRUCTURE, ELECTRICAL CONDUCTIVITY AND MAGNETISM IN AA'Fe2O6-δ, A=Sr, Ca and A'= Sr..…... 21 Introduction ………………………………………………………………….. 21 Experimental ……... …………………………………………………………. 23 Results and discussion ………………………………………………………. 25 Crystal structure ……………………………………………………... 25 Magnetic structure …………………………………………………… 33 Electrical Properties ………………………………………………..… 36 Conclusion ………………………………………………………………...…. 43 CHAPTER 3. UNRAVELING THE ROLE OF STRUCTURAL ORDER IN TRANSFORMATION OF ELECTRICAL CONDUCTIVITY IN Ca2FeCoO6-δ, CaSrFeCoO6-δ and Sr2FeCoO6-δ …………………………………………………..….. 44 ix Introduction ………………………………………………………………...…. 44 Experimental ………………………………………………………………..…. 46 Results and discussion …………………………………….…………………. 48 Crystal structure ………………………………………….…………… 48 X-ray photoelectron spectroscopy …………………………………… 61 Electrical conductivities ……………………………………...………. 65 Conclusion …………………………………………………………………….. 73 CHAPTER 4. MAGNETIC STRIUCTURE OF CaSrFeCoO5 ………………..……… 75 Introduction …………………………………………………………….……….75 Experimental section ……………………………………………….………….. 77 Results and discussion ………………………………………………………….……. 78 Conclusion ……………………………………………………………….…………… 86 CHAPTER 5. ELECTRICAL PROPERTIES OF ORDERED OXYGEN-DEFICIENT PEROVSKITE Ca2Fe0.5Ga1.5O5…………..…..……………………………………….. 87 Introduction …………………………………………….……………………. 87 Materials and methods ………………………………….……………………. 90 Results and discussion ……………………………………...……….…………91 Crystal structure …………………………………………….….……… 91 x Electrical properties ………………………………..………….……… 94 Conclusion ……………………………………………..…………..…………. 99 CHAPTER 6. ENHANCED ELECTRICAL PROPERTIES OIN BaSrFe2O6-δ (δ=0.5): A DISORDERED DEFECT-PEROVSKITE………………………..………………..…. 100 Introduction …………………………………………………….…………… 100 Experimental……… ………………………………………..……………….. 102 Results and discussion …………………………………………..…………… 103 Crystal structure …………………………………………………...…. 103 Magnetic properties ………………………………………...…………109 Electrical properties ………………………………………………….. 111 Conclusion ……………………………………………….………………….. 115 CHAPTER 7. CHARGE-TRANSPORT PROPERTIES OF Ca2FeGaO6-δ AND CaSrFeGaO6-δ: THE EFFECT OF DIFECT-ORDERED .……………………...…….. 117 Introduction ………………………………………………………………….. 117 Experimental …………………………………………….………………….. 120 Results and discussion ………………………………..……………………… 121 Crystal structure ……………………………………………….…….. 121 Microstructure and X-ray photoelectron spectroscopy studies…………125 Electrical properties ………………………………….………………. 127 Conclusion ………………………………………………………..…………. 133 xi CHAPTER 8. DISPARITY IN ELECTRICAL AND MAGNETIC PROPERTIES OF ISOSTRUCTURAL OXYGEN-DEFICIENT PEROVSKITES BaSrCo2O6-δ AND BaSrCoFeO6-δ ………..………….……………………………………………..…….. 134 Introduction ……………………………………………………….…………. 134 Experimental……… …………………………………….….………………… Results and discussion …………………………………….……...………….. Crystal structure and crystallite morphology …….………….………… X-ray photoelectron spectroscopy (XPS) and iodometric titration ….…141 Magnetic properties ……………………………………………....…… Electrical conductiviti...