(156c) Effect of Lanthanum Doping on Structure, Electronic and Elastic Properties of Perovskite, Pyrochlore Oxide and Lanthanide Titanates: A First Principles Study

Amar Deep Pathak, Foram Thakkar, Suchismita Sanyal, Hans Geerlings, Arian Nijmeijer

Fuel cells have attracted enormous interest due to their high efficiency to convert chemical energy into electrical energy with very low emission. It can be used in stationary, portable, and transport power generation. It also reduces CO₂ emissions 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 electrolyte based fuel cells operate at high temperature and are the most efficient fuel cells. They can handle variety of fuels such as H₂, CO and various hydrocarbons CH₄. [1-2]

Perovskite is a family of compound having ABX₃ type crystal structure, where A and B are cations whereas X is an anion. They exhibit variety of properties due to ferroelectric, dielectric, pyroelectric, and piezoelectric behaviours. There is paramount interest to replace conventional Ni-YSZ cermet electrode with doped perovskite in solid oxide fuel cell [3]. SrTiO₃, a member of perovskite family, is a well-known band insulator. Doping of La significantly enhance the electronic conductivity of SrTiO₃ [4]. Experimentally, perovskite (LaTiO₃), pyrochlore oxide (La₂Ti₂O₇) and lanthanide (La₂TiO₅) phase can coexist at higher temperatures (~1500 ËšC) [5]. Thus, it is essential to investigate the effect of doping in these phases of La and Sr.

In the present study, we have used GGA-DFT to investigate the various La doped structures of SrTiO₃ and Sr doped structures of La₂Ti₂O₇ and La₂TiO₅. The concentration of dopant is varied between 0-100 % considering all possible configurational structures and its dependence on electronic energy, band gap, fermi level, formation enthalpy and elastic properties are established. A change in conducting behaviour is observed as a function of doping, where a transition from band insulator to a metallic behaviour is observed by doping La in SrTiO₃, which is reversed with 100% La replacement in SrTiO₃. Such behaviour is not observed in the pyrochlore oxide phase. At the end, we shall report the preferential doping among these phase in a mixture where they all can coexist.

Reference:

[1] Kurokawa, Hideto, et al. "Y-doped SrTiO₃ based sulfur tolerant anode for solid oxide fuel cells." Journal of Power Sources 164.2 (2007): 510-518.

[2] Baniecki, J. D., et al. "Density functional theory and experimental study of the electronic structure and transport properties of La, V, Nb, and Ta doped SrTiO₃." Journal of Applied Physics 113.1 (2013): 013701.

[3] Nielsen, Jimmi, et al. "Infiltrated La_0.4Sr_0.4 Fe_0.03Ni_0.03Ti_0.94O₃ based anodes for all ceramic and metal supported solid oxide fuel cells." Journal of Power Sources 372 (2017): 99-106.

[4] Shanthi, N., and D. D. Sarma. "Electronic structure of electron doped SrTiO₃: SrTiO_3−δ and Sr_1−xLa_xTiO₃." Physical Review B 57.4 (1998): 2153.

[5] Å kapin, Srečo D., Drago Kolar, and Danilo Suvorov. "Phase stability and equilibria in the La₂O₃–TiO₂ system." Journal of the European Ceramic Society 20.8 (2000): 1179-1185.