Promoting oxygen vacancy formation and p-type conductivity in SrTiO₃via alkali metal doping: a first principles study

Abstract

Strontium titanate (SrTiO, STO) is a prototypical perovskite oxide, widely exploited in many technological applications, from catalysis to energy conversion devices. In the context of solid-oxide fuel cells, STO has been recently applied as an epitaxial substrate for nano-sized layers of mixed ion-electron conductive catalysts with enhanced electrochemical performances. To extend the applications of such heterogeneous nano-cathodes in real devices, also the STO support should be active for both electron transport and oxide diffusion. To this end, we explored using first-principles calculations the strategy of doping of STO at the Sr site with sodium and potassium. These two ions fit in the perovskite structure and induce holes in the STO valence band, so as to obtain the desired p-type electronic conduction. At the same time, the doping with alkali ions also promotes the formation of oxygen vacancies in STO, a prerequisite for effective oxide diffusion. Analysis of electron density rearrangements upon defect formation allows relating the favorable vacancy formation energies to an improved electronic delocalization over the oxide sub-lattice, as observed in closely related materials (e.g. SrFeMoO). Overall, our results suggest the alkali-doped STO as a new potential substrate material in nanoscale heterogeneous electrodes for solid oxide electrochemical cells.

Is ReO3 a mixed ionic–electronic conductor? A DFT study of defect formation and migration in a BVIO3 perovskite-type oxide

“…The high value of DE red suggests that oxygen vacancies will not be generated in any sufficient quantity by reduction, unless the conditions are extremely reducing. For comparison, we note that DFT calculations yield reduction energies for two other perovskites of 5.5-6.8 eV (SrTiO 3 ), [60][61][62][63] and 4.1-4.5 eV (LaFeO 3 ); [64][65][66][67] these are relatively close to the experimentally determined energies of reduction: 5.6-6.1 eV (SrTiO 3 ), 68,69 5.0 eV (LaFeO 3 ). 70 First, it is important to note that, for oxides with bandgaps, such as SrTiO 3 and LaFeO 3 , hybrid DFT functionals (e.g.…”

A first principles study of p-type defects in LaCrO3

“…9 The good chemical and thermal stability of the perovskite structure allow the easy dopability of LCO and the easy combination with other perovskite n-type TCOs offering a promising candidate for p-n junction applications with coherent p-n interfaces. For instance the perovskite SrTiO 3 which can be easily doped n-type [10][11][12] is shown to form a coherent interface with p-type doped LCO. 13 Doped LCO can also be a potential candidate for the contact material in the perovskite solar cells which are recently identified as a new class of solar cell materials.…”

Modifying Metastable Sr1–xBO3−δ (B = Nb, Ta, and Mo) Perovskites for Electrode Materials

“…Additionally, in comparison to reduced STO and TiO 2 , , the Fermi level for these defective SBO perovskites lies deep within either the conduction or the valence band. For SNO and SMO, the n-type conductivity arises from the partially occupied t 2g bands of the metal d orbitals. , In the case of STaO, it is believed that the partial substitution of Na into the Sr/Ta-sites of STaO significantly dopes hole carriers into the top of the valence band, resulting in the p-type conductivity . From the above calculations, the electronic structure of metastable SBO perovskites is determined to be conducive to n- or p-type transport, depending on the nature of the B-site ion, making them robust conductors.…”

“… 21 , 66 In the case of STaO, it is believed that the partial substitution of Na into the Sr/Ta-sites of STaO significantly dopes hole carriers into the top of the valence band, resulting in the p-type conductivity. 67 From the above calculations, the electronic structure of metastable SBO perovskites is determined to be conducive to n- or p-type transport, depending on the nature of the B-site ion, making them robust conductors.…”