First-Principles Study on Intrinsic Point Defects in Rhombohedral LaAlO₃ and Their Effects on Electrical Properties

Abstract

Formation energies and energy levels of various neutral and charged defects in bulk rhombohedral LaAlO3 are calculated numerically in different equilibrium conditions under different oxygen partial pressures, using first-principles plane-wave calculations. The roles of such defects in electrical properties of LaAlO3 are also discussed. The results obtained by calculations show that the formation energy becomes low for oxygen interstitial if LaAlO3 is in an oxygen-rich condition. In contrast, an oxygen vacancy is easily formed in a condition where oxygen is deficient and metal elements are relatively rich, even if the oxygen partial pressure is high. These results explain well the concentration change of constituent elements in LaAlO3 under different treatment atmospheres. Furthermore, the calculations can interpret a large tunnelling current that is often observed in a metal–oxide–silicon structure using LaAlO3 as the oxide layer, since the O vacancy has an energy level near the valence band maximum of Si.

Elucidating the effect of intrinsic defects on the dosimetric properties of the MgB4O7compound: an atomistic simulation approach

“…, is favoured by increasing the partial pressure of oxygen. 50–54 Indeed, these results are in agreement with studies showing that oxygen vacancy and interstitial oxygen defects have low formation energies in oxygen-deficient and oxygen-rich atmospheres, respectively. 53,55 Also, although negative defect pair energies are unusual, spontaneous formation processes – in the context of self-assembly 56 – have been used to design photonic crystals 57–59 under several conditions and thermodynamic constraints.…”

“…There are materials that present a negative value of the solution energy (intrinsic 42 and extrinsic 48,49 defect formation energy), wherein the formation of interstitial oxygen defects, e.g., is favoured by increasing the partial pressure of oxygen. [50][51][52][53][54] Indeed, these results are in agreement with studies…”

“…showing that oxygen vacancy and interstitial oxygen defects have low formation energies in oxygen-deficient and oxygenrich atmospheres, respectively. 53,55 Also, although negative defect pair energies are unusual, spontaneous formation processes -in the context of self-assembly 56 -have been used to design photonic crystals [57][58][59] under several conditions and thermodynamic constraints. In this case, the process of spontaneity is driven by enthalpic or entropic effects, or both, without there being a violation of the second law of thermodynamics.…”

Roles of Point Defects in Thermally Enhanced Generation and Transfer of Electrons and Holes in LaAlO3

“…We have been carrying out research on point defects in many insulating materials mainly by measuring optical absorption, photoluminescence, and electron spin resonance (ESR) spectra or by doing quantum chemical calculations for many years. [6][7][8][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Especially in LaAlO 3 , we have reported the evidence of the presence of transition metal impurities such as Fe and Cr. 16,29) In LaAlO 3 , oxygen vacancies and vacancies of positive trivalent ions (La 3þ or Al 3þ ) are also present.…”

“…16,29) In LaAlO 3 , oxygen vacancies and vacancies of positive trivalent ions (La 3þ or Al 3þ ) are also present. [29][30][31] In the previous paper, 29) we examined the effects of UV photon irradiation to LaAlO 3 on the behavior of Fe and Cr impurities, focusing on the charge transfer between the impurities and the vacancies. In the present paper, we clarify the effects of thermal annealing on these point defects in LaAlO 3 , namely their involvement in electron/hole transfer or oxidation/reduction processes by examining the changes in optical absorption and ESR spectra induced by thermal annealing in an oxidizing or a reducing atmosphere.…”