The Effect of Lanthanum Doping and Oxygen Vacancy on Perovskite, Pyrochlore Oxide and Lanthanide Titanates: A First Prin
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.41
The Effect of Lanthanum Doping and Oxygen Vacancy on Perovskite, Pyrochlore Oxide and Lanthanide Titanates: A First Principle Study Amar Deep Pathak1, Foram Thakkar1, Suchismita Sanyal1, Arian Nijmeijer2 and Hans Geerlings2 1
Shell Technology Centre, Bangalore, 562149, India.
2
Shell Technology Centre, Amsterdam, The Netherlands.
Abstract The effects of La-substitution into SrTiO3 (STO) perovskite oxides on their phase structure, formation enthalpy and electrical conductivity have been investigated. La substitution in STO has been reported to show a significant enhancement in electronic conductivity in a wideband-gap layered perovskite compound STO. Mixture of Lanthanum and Titanium oxide may lead to various phases including La2/3TiO3, La2Ti2O7 and La2TiO5. In this work, more than 50 structural models have been constructed by considering ionic state substituents, distance between substituents and their concentrations. We investigated the formation enthalpy, elastic properties and band gap by density functional theory (DFT) calculations. We have also investigated the effect of reducing environment on La 2/3TiO3. The computed bulk modulus (~2.4 % deviation) and band gap (~12% deviation) of STO are in good agreement with the literature. Our results indicate that La substitution into STO could significantly reduce the band gap. Reduction in band gap is maximum when the substituents is present at low concentrations. Internal position of La substituents in STO affects the band gap marginally while energy remains almost same. Formation enthalpy of La2/3TiO3 from LaTiO3 is around 2 eV. La2/3TiO3 acts as band insulator (band gap = 2.8 eV). In reducing environment, the band gap of La2/3TiO3 significantly reduces. Sr substitution in La2/3TiO3 lower the band gap and formation enthalpy. La2Ti2O7 and La2TiO5 have higher band gap and lower bulk modulus than STO. Sr substitution is not feasible in La2Ti2O7 and La2TiO5.
INTRODUCTION Fuel cells have attracted enormous interest due to their high efficiency to convert chemical energy into electrical energy with very low emission. They can be used in stationary, portable, and transport power generation. They also reduce the CO2
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emission when compared with the conventional hydrocarbon fuels, therefore considered as environmentally clean energy source. Fuel cells are classified based on the electrolyte/electrode material and operating temperature range. Solid oxide electrolytebased fuel cells are the most efficient fuel cells which operate at high temperature. They can handle variety of fuels such as H2, CO and various hydrocarbons such as CH4 [1,2]. Perovskite is a family of compounds having ABX3 type crystal structure, where A and B are cations whereas X is an anion. They
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