Layer-by-Layer Epitaxial Growth of Defect-Engineered Strontium Cobaltites

Abstract

Control over structure and composition of (ABO) perovskite oxides offers exciting opportunities since these materials possess unique, tunable properties. Perovskite oxides with cobalt B-site cations are particularly promising, as the range of the cation's stable oxidation states leads to many possible structural frameworks. Here, we report growth of strontium cobalt oxide thin films by molecular beam epitaxy, and conditions necessary to stabilize different defect concentration phases. In situ X-ray scattering is used to monitor structural evolution during growth, while in situ X-ray absorption near-edge spectroscopy is used to probe oxidation state and measure changes to oxygen vacancy concentration as a function of film thickness. Experimental results are compared to kinetically limited thermodynamic predictions, in particular, solute trapping, with semiquantitative agreement. Agreement between observations of dependence of cobaltite phase on oxidation activity and deposition rate, and predictions indicates that a combined experimental/theoretical approach is key to understanding phase behavior in the strontium cobalt oxide system.

High‐Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces

“…[ 234 ] In situ growth studies of metals and semiconductors using CTR scattering have a long history since the first measurements of Ge homoepitaxy via MBE by Vlieg et al [ 235 ] Homo‐ and heteroepitaxial MBE growth, [ 236–240 ] as well as metal‐organic vapor phase epitaxy (MOVPE) growth, [ 241–244 ] have been observed, leading to important basic insights into layer formation and morphology. Growth facilities built at synchrotron beamlines have enabled similar studies of complex oxide growth by MOVPE, [ 245,246 ] PLD, [ 247–250 ] and more recently, MBE, [ 232,251–253 ] revealing, for example, the tendency for certain layered structures to re‐arrange during growth [ 233,254 ] and the conditions under which oxygen defect structures are stabilized [ 100,255 ] (see Figure ). In addition to growth, in situ CTR measurements in heterogeneous environments have been carried out on crystalline‐gas [ 256 ] and crystalline‐liquid interfaces, [ 257–272 ] often relevant for geological and mineralogical studies.…”

Solute Capture and Doping of Al in Cu2O: Corrosion, Tarnish Resistance, and Cation Release of High-Purity Cu-Al Alloys in Artificial Perspiration

“…A reasonable assumption for the diffusion rate of Al in the solid state cuprous oxide is in the range of 10 −20 to 10 −30 cm 2 /s which are similar to the diffusion rates for oxide systems such as Cr in NiO (also p-type). 27,49 For a Cu-Al system, the theoretical requirements for solute capture are indeed met ( Figure 15) . Should the advancement of the oxide front exceed the speed at which the solute can diffuse to form its own oxide, the solute becomes captured as a substitutional defect in the oxide.…”

“…Should the advancement of the oxide front exceed the speed at which the solute can diffuse to form its own oxide, the solute becomes captured as a substitutional defect in the oxide. 27 Concerning the other potential fates, a physical mixture of phase pure Al 2 O 3 and Cu 2 O would require greater free energy change due to the additional interfaces (excess interfacial energy of an interface). While alumina (Al 2 O 3 ) and CuAlO 2 and CuAl 2 O 4 may be more thermodynamically favorable (Table I), these phases were not detected with Raman spectroscopy (Figure 3), GIXRD (PDF 00-035-1401 and 00-033-0448, Figure 4), or suggested from electrochemical measurements ( Figure 7, Figure 8).…”

Defects and Aliovalent Doping Engineering in Electroceramics

“…Almost all of the methods mentioned above can be utilized to in situ observe the defects such as in situ EPR, in situ XRD, − in situ XPS, in situ Raman, in situ TEM/STEM, ,− and so on. The formation and migration of defects at different temperatures, , under electric field, , or under ion-irradiated circumstance are the common research topics. In Figure A, temperature-dependent EPR spectra of Fe 3+ doped SrTiO 3 are shown .…”