Correlation between oxygen evolution reaction activity and surface compositional evolution in epitaxial LaSrNiFeO thin films.

Water electrolysis can use renewable electricity to produce green hydrogen, a portable fuel and sustainable chemical precursor. Improving electrolyzer efficiency hinges on the activity of the oxygen evolution reaction (OER) catalyst. Earth-abundant, ABO-type perovskite oxides offer great compositional, structural, and electronic tunability, with previous studies showing compositional substitution can increase the OER activity drastically.

Understanding the Electronic Structure Evolution of Epitaxial LaNiFeO Thin Films for Water Oxidation.

Rare earth nickelates including LaNiO are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO. However, the role of Fe in increasing the activity remains ambiguous, with potential origins that are both structural and electronic in nature.

Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces.

Mastery of order-disorder processes in highly nonequilibrium nanostructured oxides has significant implications for the development of emerging energy technologies. However, we are presently limited in our ability to quantify and harness these processes at high spatial, chemical, and temporal resolution, particularly in extreme environments. Here, we describe the percolation of disorder at the model oxide interface LaMnO/SrTiO, which we visualize during ion irradiation in the transmission electron microscope.

Incorporation of Ti in epitaxial FeTiOthin films.

The titanomagnetites (FeTiO,⩽ 1) are a family of reducible spinel-structure oxides of interest for their favorable magnetic, catalytic, and electrical transport properties. To understand the stability of the system during low temperature deposition, epitaxial thin films of FeTiOwere deposited by molecular beam epitaxy (MBE) on MgO(001) at 250-375 °C. The homogeneous incorporation of Ti, Fe valence state, and film morphology were all found to be strongly dependent on the oxidation conditions at the low substrate temperatures employed.

Electronic and structural properties of single-crystal Jahn-Teller active Co Mn O thin films.

Recent investigations on spinel CoMnO have shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline Co Mn O thin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry.

Electronic and Structural Properties of Single-crystal Jahn-Teller Active CoMnOThin Films.

Recent investigations on spinel CoMnOhave shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline CoMnOthin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry.

Reversible Oxidation Quantified by Optical Properties in Epitaxial FeCrO Films on (001) MgAlO.

We report on the structural and optical properties of FeCrO epitaxial films grown by molecular beam epitaxy on MgAlO (001) as a function of δ (average cation valence). The average Fe valence is linked to the out-of-plane lattice parameter and the extent of light absorption in the infrared spectral region. Over-oxidized films (0 < δ < 0.

Effect of structure and composition on the electronic excitation induced amorphization of LaTiZrO ceramics.

Understanding the response of ceramics operating in extreme environments is of interest for a variety of applications. Ab initio molecular dynamic simulations have been used to investigate the effect of structure and B-site (=Ti, Zr) cation composition of lanthanum-based oxides (LaBO) on electronic-excitation-induced amorphization. We find that the amorphous transition in monoclinic layered perovskite LaTiO occurs for a lower degree of electronic excitation than for cubic pyrochlore LaZrO.

Tuning piezoelectric properties through epitaxy of LaTiO and related thin films.

Current piezoelectric sensors and actuators are limited to operating temperatures less than ~200 °C due to the low Curie temperature of the piezoelectric material. Strengthening the piezoelectric coupling of high-temperature piezoelectric materials, such as LaTiO (LTO), would allow sensors to operate across a broad temperature range. The crystalline orientation and piezoelectric coupling direction of LTO thin films can be controlled by epitaxial matching to SrTiO(001), SrTiO(110), and rutile TiO(110) substrates via pulsed laser deposition.

Effect of doping and chemical ordering on the optoelectronic properties of complex oxides: FeO-VO solid solutions and hetero-structures.

The electronic and optical properties of α-(FeV)O at low (x = 0.04) and high (x = 0.5) doping levels are investigated using a combination of periodic and embedded cluster approaches, and time-dependent density functional theory.

Effect of Sr Content and Strain on Sr Surface Segregation of LaSrCoFeO as Cathode Material for Solid Oxide Fuel Cells.

Strontium-doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, and reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as surface segregation of Sr during solid oxide fuel cell (SOFC) operation, which can adversely affect the electrochemical performance. Thus, understanding the nature of the Sr surface segregation phenomenon and how it is affected by the composition of LSCF and strain are critical.

Infrared optical absorption in low-spin Fe(2+)-doped SrTiO3.

Band gap engineering in SrTiO3 and related titanate perovskites has long been explored due to the intriguing properties of the materials for photocatalysis and photovoltaic applications. A popular approach in the materials chemistry community is to substitutionally dope aliovalent transition metal ions onto the B site in the lattice to alter the valence band. However, in such a scheme there is limited control over the dopant valence, and compensating defects often form.

Built-In Potential in Fe2O3-Cr2O3 Superlattices for Improved Photoexcited Carrier Separation.

Hematite (α-Fe2 O3) is engineered to improve photoexcited electron-hole pair separation by synthesizing Fe2O3-Cr2O3 superlattices (SLs) with precise atomic control. The different surface terminations exhibited by Fe2O3 and Cr2O3 determine the hetero-junction interface structure and result in controllable, noncommutative band offset values. This controllable band alignment is harnessed to generate a built-in potential as large as 0.

Optical absorption and spectral photoconductivity in α-(Fe₁-xCrx)₂O₃ solid-solution thin films.

Hematite, α-Fe2O3, is an attractive narrow gap oxide for consideration as an efficient visible light photocatalyst, with significant potential for band gap engineering via doping. We examine optical absorption in α-(Fe1-xCrx)2O3 epitaxial films and explain the observed excitations, and the nature of the band gap dependence on x, through first-principles calculations. The calculated and measured optical band gap becomes smaller than that of bulk α-Fe2O3 and reaches a minimum as the Cr cation fraction increases to 50%.

Multilayered YSZ/GZO films with greatly enhanced ionic conduction for low temperature solid oxide fuel cells.

Strain confinement in heterostructured films significantly affects ionic conductivity of the electrolytes for solid oxide fuel cells based on a multi-layered design strategy. Nearly ideal tensile strain can be achieved by a dedicated manipulation of the lattice mismatch between adjacent layers and fine control of the layer thicknesses to minimize the formation of dislocations and thus to achieve optimized ionic conduction. This strategy was demonstrated by a model system of multilayered 8 mol%Y(2)O(3) stabilized ZrO(2) (YSZ) with Gd(2)Zr(2)O(7) (GZO) films, which were epitaxially grown on Al(2)O(3) (0001) substrates by pulsed laser deposition (PLD) with the {111} planes of YSZ/GZO along the Al(2)O(3) [0 1 -1 0] direction.

Magnetotransport properties of high quality Co:ZnO and Mn:ZnO single crystal pulsed laser deposition films: pitfalls associated with magnetotransport on high resistivity materials.

The electrical resistivity values for a series of pure and doped (Co, Mn, Al) ZnO epitaxial films grown by pulsed laser deposition were measured with equipment designed for determining the direct current resistivity of high resistance samples. Room-temperature resistances ranging from 7 x 10(1) to 4 x 10(8) Omega/sq were measured on vacuum-reduced cobalt-doped ZnO, (Al,Co) co-doped ZnO, pure cobalt-doped ZnO, Mn-doped ZnO, and undoped ZnO. Using a four-point collinear geometry with gold spring-loaded contacts, resistivities were measured from 295 to 5 K for resistances of < approximately 10(12) Omega/sq.