Interplay between strain, defect charge state, and functionality in complex oxides

Abstract

We use first-principles calculations to investigate the interplay between strain and the charge state of point defect impurities in complex oxides. Our work is motivated by recent interest in using defects as active elements to provide novel functionality in coherent epitaxial films. Using oxygen vacancies as model point defects, and CaMnO3 and MnO as model materials, we calculate the changes in internal strain caused by changing the charge state of the vacancies, and conversely the effect of strain on charge-state stability. Our results show that the charge state is a degree of freedom that can be used to control the interaction of defects with strain and hence the concentration and location of defects in epitaxial films. We propose the use of field-effect gating to reversibly change the charge state of defects and hence the internal strain and corresponding strain-induced functionalities.

The Misfit Dislocation Core Phase in Complex Oxide Heteroepitaxy

“…This behavior strongly on the axial plane. On the other hand, the inbalance between La enrichment and Sr depletion suggests that the vacancy formation energy is further reduced under tensile strain, in agreement with atomistic simulations of dislocations in CeO 2 [12] and STO [11], and biaxially strained thin films of CaMnO 3 [60,61].…”

Oxygen vacancy dipoles in strained epitaxial BaTiO3 films

“…The links between strain and oxygen vacancies are highlighted by recent first-principles analyses [18][19][20]. Compared to unstressed perovskite oxide ferroelectric, an in-plane compressive strain strongly reduces the formation energy for an out-of-plane oxygen vacancy [20].…”

“…In practice, the oxygen vacancies form to compensate the charge imbalance induced by heterovalent doping and/or in the result of oxygen-deficient processing such as synthesis or annealing in a reducing atmosphere [11][12][13], or during thinfilm deposition at sufficiently low oxygen pressures [14][15][16]. In epitaxial films, the influence of lattice strain on the formation of oxygen vacancies was also recently recognized [17][18][19][20].…”

In situ anion-doped epitaxial strontium titanate films

“…3 Another recently revealed essential consequence of misfit strain is the reduction of the formation energy for oxygen vacancies (V O ) in perovskite oxides. [4][5][6][7] These oxygen vacancies may offer unoccupied lattice sites for anion dopants, therefore, the misfit-promoted formation of oxygen vacancies may facilitate the substitutional incorporation of anion dopants in epitaxial films. Moreover, as recently found in epitaxial BaTiO 3 films, 8,9 a misfit strain can control the orientation of the Ti-V O -Ti complexes and determine the specific locations of the vacancies in selected atomic planes.…”