We have investigated heteroepitaxial films of Sm-doped BiFeO 3 with a Sm-concentration near a morphotropic phase boundary. Our high-resolution synchrotron X-ray diffraction, carried out in a temperature range of 25°C to 700°C, reveals substantial phase coexistence as one changes temperature to crossover from a low-temperature PbZrO 3 -like phase to a high-temperature orthorhombic phase. We also examine changes due to strain for films exhibiting anisotropic misfit between film and substrate. Additionally, thicker films exhibit a substantial volume collapse associated with the structural transition that is suppressed in thinner films.

We have synthesized and characterized laser-deposited film samples of perovskite BaCrO3, a missing member of the perovskite-chromate family. The BaCrO3 films have a substantially larger lattice constant than other chromates, are insulating, and exhibit weak ferromagnetism. Employing firstprinciples density functional theory calculations, we attribute such weak ferromagnetism to a canted C-type antiferromagnetic spin order. Additionally, comparison with the other sister compounds CaCrO3 and SrCrO3 suggests an anomalous Mott transition where magnetism is independent of whether the compound is metallic or insulating.Transition metal oxides (TMOs) with perovskite and related structures exhibit many fascinating electronic phenomena, including Mott insulators, metalinsulator transitions, and high-Tc superconductivity, due to transport being determined by strongly correlated d electrons.1 One of the ubiquitous questions for these compounds is how exactly transport is coupled to magnetic degrees of freedom. The textbook situation is that ferromagnetism leads to metallic conductivity, while antiferromagnetism is associated with non-conducting behavior, particularly Mott insulators. A classic example is colossal magnetoresistance in the manganites, where a magnetic field can induce a transition from an insulating antiferromagnetic phase to a conducting ferromagnetic phase. 2There are some exceptions which indicate other new phenomena may be in play. Observations of ferromagnetic insulators and antiferromagnetic conductors are most often explained by particular orbital orderings 3 or reduced electronic and structural dimensionality.4 This report describes the properties of a new end member of a family that can be driven through a metal-insulator transition using chemical pressure, or bandwidth control, yet seems to retain the same magnetic structure on both sides of the transition. We have synthesized BaCrO 3 in perovskite form by using epitaxial film growth on an appropriate crystal template. This polymorph is apparently not stable in the bulk.Four decades ago, a few chromate perovskites ACrO 3 (A = Ca, Sr, and Pb) were synthesized by several groups using solid-state reaction techniques with high pressure (≈ 6-10 GPa) and high temperature (≈ 1000 K).5−9 Recent studies on CaCrO 3 and SrCrO 3 have exhibted some novel properties, drawing more attention to these chromate compounds.10−16 For example, both of these compounds are antiferromagnetic conductors. It is also suggested that CaCrO 3 possibly lies in the crossover region between being itinerant and localized, implying the necessity to consider correlation effects.14,15 An interesting orbital ordering transition and electronic phase coexistence have been discovered in SrCrO 3 .12 Among these chromate compounds, only PbCrO 3 is unambiguously thought to be an insulator with the G-type AFM spin structure. However, because of the different outer orbital configuration of Pb, PbCrO 3 can hardly be used to form a unified scheme to understand the exotic properties of the other c...

A targeted mass spectrometry-based method is presented that adopts the fast photochemical oxidation of proteins (FPOP) for footprinting of cystic fibrosis transmembrane conductance regulator (CFTR) membrane transporter at its original plasma membrane location. Two analytical imperatives were sought: (1) overall simplification in data acquisition and analysis and (2) lower quantitation limits, which enabled direct analysis of intrinsically low-abundance transmembrane proteins. These goals were achieved by using a reversed-footprinting technique that monitored the unoxidized peptides remaining after the FPOP treatment. In searching for structurally informative peptides, a workflow was designed for accurate and precise quantitation of CFTR peptides produced from proteolytically digesting the plasma membrane subproteome of cells. This sample preparation strategy mitigated the need for challenging purification of large quantities of structurally intact CFTR. On the basis of the interrogated peptides, it was proposed a concept of the structural marker peptide that could report CFTR structure and function in cells. The reversed-footprinting mass spectrometry extends the FPOP technology to study conformation and interaction changes of low-abundance proteins directly in their endogenous cellular locations.

Using pulsed laser deposition and a unique fast quenching method, we have prepared SrCoO x epitaxial films on SiTiO 3 substrates. As electrochemical oxidation increases the oxygen content from x = 2.75 to 3.0, the films tend to favor the discrete magnetic phases seen in bulk samples for the homologous series SrCoO (3-n/8) (n = 0, 1, 2). Unlike bulk samples, 200nm thick films remain single phase throughout the oxidation cycle. 300 nm films can show two simultaneous phases during deoxidation. These results are attributed to finite thickness effects and imply the formation of ordered regions larger than approximately 300 nm.Many transition metal oxides exhibit a rich phase diagram as electron interactions result in multiple ground states with comparable energy. Of particular interest are doped correlated-insulators, where charge doping, often leads to electronic inhomogeneity and in some cases results in clear electronic phase separation.

Two magnetic phase transitions have been noted for SrCoO3−y for near-stoichiometric oxygen concentrations (small y). Using muon spin rotation and neutron scattering experiments, we have established that the two transitions represent separate, spatially distinct magnetic phases that coexist in a two-phase equilibrium mixture. The two phases most likely represent areas of the sample with different effective valence charge density. Further, the phases exist over regions with a length scale intermediate between nanoscale charge inhomogeneity and systems such as manganites or super-oxygenated cuprates with large length scale phase separation.