Vibrations and Phase Stability in Mixed Valence Antimony Oxide.

α-Sb2O4 (cervantite) and ß-Sb2O4 (clinocervantite) are mixed valence compounds with equal proportions of SbIII and SbV as represented in the formula SbIIISbVO4. Their structure and properties can be difficult to calculate owing to the SbIII lone-pair electrons. Here, we present a study of the lattice dynamics and vibrational properties using a combination of inelastic neutron scattering, Mössbauer spectroscopy, nuclear inelastic scattering, and density functional theory (DFT) calculations. DFT calculations that account for lone-pair electrons match the experimental densities of phonon states. Mössbauer spectroscopy reveals the ß phase to be significantly harder than the α phase. Calculations with O vacancies reveal the possibility for nonstoichiometric proportions of SbIII and SbV in both phases. An open question is what drives the stability of the α phase over the ß phase, as the latter shows pronounced kinetic stability and lower symmetry despite being in the high-temperature phase. Since the vibrational entropy difference is small, it is unlikely to stabilize the α phase. Our results suggest that the α phase is more stable only because the material is not fully stoichiometric.

Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides.

High-entropy oxides (HEOs) have attracted great interest in diverse fields because of their inherent opportunities to tailor and combine materials functionalities. The control of local order/disorder in the class is by extension a grand challenge toward realizing their vast potential. Here we report the first examples of pyrochlore HEOs with five M-site cations, for Nd2M2O7, in which the local structure has been investigated by neutron diffraction and pair distribution function (PDF) analysis. The average structure of the pyrochlores is found to be orthorhombic Imma, in agreement with radius-ratio rules governing the structural archetype. The computed PDFs from density functional theory relaxed special quasirandom structure models are compared with real space PDFs in this work to evaluate M-site order/disorder. Reverse Monte Carlo combined with ab initio molecular dynamics and Metropolis Monte Carlo simulations demonstrates that Nd2(Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2)2O7 is synthesized with its M-site local to nanoscale order highly randomized/disordered, while Nd2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)2O7+x exhibits a strong distortion of the TiO6 octahedron and small degree of Ti chemical short-range order (SRO) on the subnanometer scale. Calculations suggest that this may be intrinsic, energetically favored SRO rather than due to sample processing. These results offer an important demonstration that the engineered variation of participating ions in HEOs, even among those with very similar radii, provides richly diverse opportunities to control local order/disorder motifs-and therefore materials properties for future designs. This work also hints at the exquisite level of detail that may be needed in computational and experimental data analysis to guide structure-property tuning in the emerging HEO materials class.

Role of Pairwise Reactions on the Synthesis of Li0.3La0.57TiO3 and the Resulting Structure-Property Correlations.

The performance of single-ion conductors is highly sensitive to the material's defect chemistry. Tuning these defects is limited for solid-state reactions as they occur at particle-particle interfaces, which provide a complex evolving energy landscape for atomic rearrangement and product formation. In this report, we investigate the (1) order of addition and (2) lithium precursor decomposition temperature and their effect on the synthesis and grain boundary conductivity of the perovskite lithium lanthanum titanium oxide (LLTO). We use an intimately mixed sol-gel, a solid-state reaction of Li precursor + La2O3 + TiO2, and Li precursor + amorphous La0.57TiOx as different chemical routes to change the way in which the elements are brought together. The results show that the perovskite can accommodate a wide range of Li deficiencies (upward of 50%) while maintaining the tetragonal LLTO structure, indicating that X-ray diffraction (XRD) is insufficient to fully characterize the chemical nature of the product (i.e., Li-deficient LLTO may behave differently than stoichiometric LLTO). Variations in the relative intensities of different reflections in XRD suggest variations in the La ordering within the crystal structure between synthesis methods. Furthermore, the choice of the precursor and the order of addition of the reactants lower the time required to form a pure phase. Density functional theory calculations of the formation energy of possible reaction intermediates support the hypothesis that a greater thermodynamic driving force to form LLTO leads to a greater LLTO yield. The retention of lithium is correlated with the thermal decomposition temperature of the Li precursor and the starting material mixing strategy. Taking the results together suggests that cations that share a site with Li should be mixed early to avoid ordering. Such cation ordering inhibits Li motion, leading to higher Li ion resistance.

From Molecules to Solids: A vdW-DF-C09 Case Study of the Mercury Dihalides.

The mercury dihalides show a remarkable diversity in the structural preferences in their minimum energy structure types, spanning molecular to strongly bound ionic solids. A challenge in the development of density functional methods for extended systems is to arrive at strategies that serve equally well such a broad range of bonding modes or structural preferences. The chemical bonding and the stabilities of mercury dihalides and the general utility and reliability of the van der Waals density functional with C09 exchange (vdW-DF-C09) in predicting or describing the energetics and structural preferences in these metal dihalides is examined. We show that, in contrast with the uncorrected generalized gradient approximation of the Perdew-Burke-Erzenhoff (PBE) exchange-correlation functional, qualitative and quantitative patterns in the bonding of the mercury dihalide solids are well reproduced with vdW-DF-C09 for the full series of HgX2 systems for X = F, Cl, Br, and I. The possible existence of a low-temperature cotunnite polymorph for HgF2 and PbF2 is posited.

Perspectives on van der Waals Density Functionals: The Case of TiS2.

The van der Waals interaction is of foundational importance for a wide variety of physical systems. In particular, van der Waals forces lie at the heart of potential device technologies that may be realized from the functional organization of layered two-dimensional (2D) nanomaterials. For intermediate to large-scale applications modeling, van der Waals density functionals have become the de facto choice for first-principles calculations. In particular, the vdW-DF family of functionals have provided a systematic approach to this theoretically challenging problem. While much progress has been made, there remains room for improvement in the microscopic description of vdW forces from these density functionals. In this work, we compute benchmark results for the binding energy and the electronic density response to binding in TiS2 via accurate diffusion quantum Monte Carlo calculations. We compare these benchmark data to results obtained from local, semilocal, and van der Waals functionals. In particular, we gauge the quality of the original vdW-DF/vdW-DF2 functionals, as well as updated variants such as vdW-DF-C09, vdW-DF-optB88, vdW-DF-optB86b, and vdW-DF2-B86R. We find a close relationship between the accuracy of predicted interlayer separation distances and binding energies for TiS2, with the vdW-DF-optB88 functional performing very well in terms of both quantities. In general, the more recently developed functionals are systematic improvements over older ones. However, when considering the response of the electron density to binding, we find that local-density approximation (LDA) and PBEsol generally outperform the vdW-DF functionals in describing the interlayer charge accumulation with vdW-DF-C09 variants performing the best overall.

Tuning oxygen electrocatalysis via strain on LaNiO3(001).

The slow kinetics of the oxygen evolution (OER) and oxygen reduction (ORR) reactions hamper the development of renewable energy storage and conversion technologies. Transition-metal oxides (TMOs) are cost-effective replacements to conventional noble metal catalysts for driving these electrochemical systems. Strain is known to greatly affect the electronic structure of TMO surfaces, leading to significant changes in their electrocatalytic activities. In this study, we explore the influence of strain on the OER and ORR mechanisms on the LaNiO3(001) surface using density functional theory (DFT). Through a comparison of the overpotential and the largest change in Gibbs free energy (ΔG) in the reaction pathway, we determined that the OER activity on the LaNiO3 surface is directly related to the desorption of -H from the surface, which can be tuned as a function of strain. Moreover, tensile strain shuts off the reaction pathway to forming the -O2H intermediate state, due to the dissociation of -O2H into -O2 and -H. This is largely a consequence of the strong binding of H to the surface O, leading to a significant increase in the largest ΔG for the ORR on the tensile-strained surfaces by promoting an alternative reaction pathway. Overall, our results show that tensile strain on LaNiO3(001) leads to a decrease in both OER and ORR activities. Interestingly, in both cases, we find that the reaction is driven by the interactions with surface O ions, thus calling for a reinterpretation of the role that Ni eg orbital polarization plays in defining the OER and ORR catalytic activity on the TMO surfaces. Here, it is an indirect measure of changes in Ni-O hybridization, which controls the binding of -H species to the surface. As such, these results highlight the importance of surface O ions; particularly as it relates to defining molecule-surface interactions that ultimately tune and enhance the electrocatalytic efficiency of perovskite materials through the modulation of strains.

Corticotropin-releasing factor overexpression gives rise to sex differences in Alzheimer's disease-related signaling.

Several neuropsychiatric and neurodegenerative disorders share stress as a risk factor and are more prevalent in women than in men. Corticotropin-releasing factor (CRF) orchestrates the stress response, and excessive CRF is thought to contribute to the pathophysiology of these diseases. We previously found that the CRF1 receptor (CRF1) is sex biased whereby coupling to its GTP-binding protein, Gs, is greater in females, whereas ß-arrestin-2 coupling is greater in males. This study used a phosphoproteomic approach in CRF-overexpressing (CRF-OE) mice to test the proof of principle that when CRF is in excess, sex-biased CRF1 coupling translates into divergent cell signaling that is expressed as different brain phosphoprotein profiles. Cortical phosphopeptides that distinguished female and male CRF-OE mice were overrepresented in unique pathways that were consistent with Gs-dependent signaling in females and ß-arrestin-2 signaling in males. Notably, phosphopeptides that were more abundant in female CRF-OE mice were overrepresented in an Alzheimer's disease (AD) pathway. Phosphoproteomic results were validated by demonstrating that CRF overexpression in females was associated with increased tau phosphorylation and, in a mouse model of AD pathology, phosphorylation of ß-secretase, the enzyme involved in the formation of amyloid ß. These females exhibited increased formation of amyloid ß plaques and cognitive impairments relative to males. Collectively, the findings are consistent with a mechanism whereby the excess CRF that characterizes stress-related diseases initiates distinct cellular processes in male and female brains, as a result of sex-biased CRF1 signaling. Promotion of AD-related signaling pathways through this mechanism may contribute to female vulnerability to AD.

Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO3 Perovskites.

Strain is known to greatly influence low-temperature oxygen electrocatalysis on noble metal films, leading to significant enhancements in bifunctional activity essential for fuel cells and metal-air batteries. However, its catalytic impact on transition-metal oxide thin films, such as perovskites, is not widely understood. Here, we epitaxially strain the conducting perovskite LaNiO3 to systematically determine its influence on both the oxygen reduction and oxygen evolution reaction. Uniquely, we found that compressive strain could significantly enhance both reactions, yielding a bifunctional catalyst that surpasses the performance of noble metals such as Pt. We attribute the improved bifunctionality to strain-induced splitting of the eg orbitals, which can customize orbital asymmetry at the surface. Analogous to strain-induced shifts in the d-band center of noble metals relative to the Fermi level, such splitting can dramatically affect catalytic activity in this perovskite and other potentially more active oxides.

Bisphenol A environmental exposure and the detrimental effects on human metabolic health: is it necessary to revise the risk assessment in vulnerable population?

In the last decades, many reports have focused the attention on deleterious effects of novel environmental chemical compounds, including bisphenol A (BPA), on human health. BPA, a common and widely chemical contaminant acting as endocrine disruptor, accumulates in adipose tissue and may affect adipocyte metabolic and inflammatory functions. BPA, at low chronic doses, is now considered as an obesogen compound, and might contribute to the rise of metabolic syndrome, visceral adiposity and diabetes epidemics. The BPA worldwide presence in the environment is responsible for chronic exposure during vulnerable periods, such as foetal and neonatal life. The BPA source of contamination can occur via food, beverage, wastewater, air, dust and soil. BPA, as lipophilic compound, may accumulate into the adipose tissue already during foetal life and may affect adulthood health, through adverse effects on the growth and development of organs and tissues. Thus, based on several studies, it would be crucial to consider further actions aimed to refine risk assessment at least in vulnerable population, such as foetuses, infants and young children, to prevent metabolic diseases and obesity.

van der Waals forces in density functional theory: a review of the vdW-DF method.

A density functional theory (DFT) that accounts for van der Waals (vdW) interactions in condensed matter, materials physics, chemistry, and biology is reviewed. The insights that led to the construction of the Rutgers-Chalmers van der Waals density functional (vdW-DF) are presented with the aim of giving a historical perspective, while also emphasizing more recent efforts which have sought to improve its accuracy. In addition to technical details, we discuss a range of recent applications that illustrate the necessity of including dispersion interactions in DFT. This review highlights the value of the vdW-DF method as a general-purpose method, not only for dispersion bound systems, but also in densely packed systems where these types of interactions are traditionally thought to be negligible.

Increased vulnerability of the brain norepinephrine system of females to corticotropin-releasing factor overexpression.

Stress-related psychiatric disorders are more prevalent in women than men. As hypersecretion of the stress neuromediator, corticotropin-releasing factor (CRF) has been implicated in these disorders, sex differences in CRF sensitivity could underlie this disparity. Hyperarousal is a core symptom that is shared by stress-related disorders and this has been attributed to CRF regulation of the locus ceruleus (LC)-norepinephrine arousal system. We recently identified sex differences in CRF(1) receptor (CRF(1)) signaling and trafficking that render LC neurons of female rats more sensitive to CRF and potentially less able to adapt to excess CRF compared with male rats. The present study used a genetic model of CRF overexpression to test the hypothesis that females would be more vulnerable to LC dysregulation by conditions of excess CRF. In both male and female CRF overexpressing (CRF-OE) mice, the LC was more densely innervated by CRF compared with wild-type controls. Despite the equally dense CRF innervation of the LC in male and female CRF-OE mice, LC discharge rates recorded in slices in vitro were selectively elevated in female CRF-OE mice. Immunoelectron microscopy revealed that this sex difference resulted from differential CRF(1) trafficking. In male CRF-OE mice, CRF(1) immunolabeling was prominent in the cytoplasm of LC neurons, indicative of internalization, a process that would protect cells from excessive CRF. However, in female CRF-OE mice, CRF(1) labeling was more prominent on the plasma membrane, suggesting that the compensatory response of internalization was compromised. Together, the findings suggest that the LC-norepinephrine system of females will be particularly affected by conditions resulting in elevated CRF because of differences in receptor trafficking. As excessive LC activation has been implicated in the arousal components of stress-related psychiatric disorders, this may be a cellular mechanism that contributes to the increased incidence of these disorders in females.

Composition dependent intrinsic defect structures in SrTiO3.

Intrinsic point defect complexes in SrTiO3 under different chemical conditions are studied using density functional theory. The Schottky defect complex consisting of nominally charged Sr, Ti and O vacancies is predicted to be the most stable defect structure in stoichiometric SrTiO3, with a relatively low formation energy of 1.64 eV per defect. In addition, the mechanisms of defect complex formation in nonstoichiometric SrTiO3 are investigated. Excess SrO leads to the formation of oxygen vacancies and a strontium-titanium antisite defect, while a strontium vacancy together with an oxygen vacancy and a titanium-strontium antisite defect are produced in an excess TiO2 environment. Since point defects, such as oxygen vacancies and cation antisite defects, are intimately related to the functionality of SrTiO3, these results provide guidelines for controlling the formation of intrinsic point defects and optimizing the functionality of SrTiO3 by controlling nonstoichiometric chemical compositions of SrO and TiO2 in experiments.

Growth-promoting action and growth factor release by different platelet derivatives.

Abstract Platelet derivatives are commonly used in wound healing and tissue regeneration. Different procedures of platelet preparation may differentially affect growth factor release and cell growth. Preparation of platelet-rich fibrin (PRF) is accompanied by release of growth factors, including platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and transforming growth factor ß1 (TGFß1), and several cytokines. When compared with the standard procedure for platelet-rich plasma (PRP), PRF released 2-fold less PDGF, but >15-fold and >2-fold VEGF and TGFß1, respectively. Also, the release of several cytokines (IL-4, IL-6, IL-8, IL-10, IFNγ, MIP-1α, MIP-1ß and TNFα) was significantly increased in PRF-conditioned medium (CM), compared to PRP-CM. Incubation of both human skin fibroblasts and human umbilical vein endothelial cells (HUVECs) with PRF-derived membrane (mPRF) or with PRF-CM enhanced cell proliferation by >2-fold (p<0.05). Interestingly, PRP elicited fibroblast growth at a higher extent compared to PRF. At variance, PRF effect on HUVEC growth was significantly greater than that of PRP, consistent with a higher concentration of VEGF in the PRF-CM. Thus, the procedure of PRP preparation leads to a larger release of PDGF, as a possible result of platelet degranulation, while PRF enhances the release of proangiogenic factors.

van der Waals density functionals built upon the electron-gas tradition: facing the challenge of competing interactions.

The theoretical description of sparse matter attracts much interest, in particular for those ground-state properties that can be described by density functional theory. One proposed approach, the van der Waals density functional (vdW-DF) method, rests on strong physical foundations and offers simple yet accurate and robust functionals. A very recent functional within this method called vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)] stands out in its attempt to use an exchange energy derived from the same plasmon-based theory from which the nonlocal correlation energy was derived. Encouraged by its good performance for solids, layered materials, and aromatic molecules, we apply it to several systems that are characterized by competing interactions. These include the ferroelectric response in PbTiO3, the adsorption of small molecules within metal-organic frameworks, the graphite/diamond phase transition, and the adsorption of an aromatic-molecule on the Ag(111) surface. Our results indicate that vdW-DF-cx is overall well suited to tackle these challenging systems. In addition to being a competitive density functional for sparse matter, the vdW-DF-cx construction presents a more robust general-purpose functional that could be applied to a range of materials problems with a variety of competing interactions.

Putting error bars on density functional theory.

Predicting the error in density functional theory (DFT) calculations due to the choice of exchange-correlation (XC) functional is crucial to the success of DFT, but currently, there are limited options to estimate this a priori. This is particularly important for high-throughput screening of new materials. In this work, the structure and elastic properties of binary and ternary oxides are computed using four XC functionals: LDA, PBE-GGA, PBEsol, and vdW-DF with C09 exchange. To analyze the systemic errors inherent to each XC functional, we employed materials informatics methods to predict the expected errors. The predicted errors were also used to better the DFT-predicted lattice parameters. Our results emphasize the link between the computed errors and the electron density and hybridization errors of a functional. In essence, these results provide "error bars" for choosing a functional for the creation of high-accuracy, high-throughput datasets as well as avenues for the development of XC functionals with enhanced performance, thereby enabling the accelerated discovery and design of new materials.

Reversal of the lattice structure in SrCoO(x) epitaxial thin films studied by real-time optical spectroscopy and first-principles calculations.

Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoO(x) (x=2.5-3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases: i.e., the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First-principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator transition, which originate from the modification in the Co valence states and crystallographic structures. More interestingly, the two phases can be reversibly controlled by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides.

Fractionally δ-doped oxide superlattices for higher carrier mobilities.

A two-dimensional (2D) electron gas system in an oxide heterostructure serves as an important playground for novel phenomena. Here, we show that, by using fractional δ-doping to control the interface's composition in La(x)Sr(1-x)TiO(3)/SrTiO(3) artificial oxide superlattices, the filling-controlled 2D insulator-metal transition can be realized. The atomic-scale control of d-electron band filling, which in turn contributes to the tuning of effective mass and density of the charge carriers, is found to be a fascinating route to substantially enhanced carrier mobilities.

(Mg,Mn,Fe,Co,Ni)O: A rocksalt high-entropy oxide containing divalent Mn and Fe.

High-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating to their structure formation, phase stability, and the interplay between configurational disorder and physical and chemical properties. Introducing Fe(II) and Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this structure under ambient conditions. Here, we develop a bottom-up method for synthesizing Mn- and Fe-containing rocksalt HEO (FeO-HEO). We present a comprehensive investigation of its crystal structure and the random cation-site occupancy. We show the improved structural robustness of this FeO-HEO and verify the viability of an oxygen sublattice as a buffer layer. Compositional analysis reveals the valence and spin state of the iron species. We further report the antiferromagnetic order of this FeO-HEO below the transition temperature ~218 K and predict the conditions of phase stability of Mn- and Fe-containing HEOs. Our results provide fresh insights into the design and property tailoring of emerging classes of HEOs.

High Entropy Oxide Relaxor Ferroelectrics.

Relaxor ferroelectrics are important in technological applications due to strong electromechanical response, energy storage capacity, electrocaloric effect, and pyroelectric energy conversion properties. Current efforts to discover and design materials in this class generally rely on substitutional doping as slight changes to local compositional order can significantly affect the Curie temperature, morphotropic phase boundary, and electromechanical responses. In this work, we demonstrate that moving to the strong limit of compositional complexity in an ABO3 perovskite allows stabilization of relaxor responses that do not rely on a single narrow phase transition region. Entropy-assisted synthesis approaches are utilized to synthesize single-crystal Ba(Ti0.2Sn0.2Zr0.2Hf0.2Nb0.2)O3 [Ba(5B)O] films. The high levels of configurational disorder present in this system are found to influence dielectric relaxation, phase transitions, nanopolar domain formation, and Curie temperature. Temperature-dependent dielectric, Raman spectroscopy, and second-harmonic generation measurements reveal multiple phase transitions, a high Curie temperature of 570 K, and the relaxor ferroelectric nature of Ba(5B)O films. The first-principles theory calculations are used to predict possible combinations of cations to design relaxor ferroelectrics and quantify the relative feasibility of synthesizing these highly disordered single-phase perovskite systems. The ability to stabilize single-phase perovskites with various cations on the B-sites offers possibilities for designing high-performance relaxor ferroelectric materials for piezoelectric, pyroelectric, and electrocaloric applications.

Sex differences in corticotropin-releasing factor receptor signaling and trafficking: potential role in female vulnerability to stress-related psychopathology.

Although the higher incidence of stress-related psychiatric disorders in females is well documented, its basis is unknown. Here, we show that the receptor for corticotropin-releasing factor (CRF), the neuropeptide that orchestrates the stress response, signals and is trafficked differently in female rats in a manner that could result in a greater response and decreased adaptation to stressors. Most cellular responses to CRF in the brain are mediated by CRF receptor (CRFr) association with the GTP-binding protein, G(s). Receptor immunoprecipitation studies revealed enhanced CRFr-G(s) coupling in cortical tissue of unstressed female rats. Previous stressor exposure abolished this sex difference by increasing CRFr-G(s) coupling selectively in males. These molecular results mirrored the effects of sex and stress on sensitivity of locus ceruleus (LC)-norepinephrine neurons to CRF. Differences in CRFr trafficking were also identified that could compromise stress adaptation in females. Specifically, stress-induced CRFr association with beta-arrestin2, an integral step in receptor internalization, occurred only in male rats. Immunoelectron microscopy confirmed that stress elicited CRFr internalization in LC neurons of male rats exclusively, consistent with reported electrophysiological evidence for stress-induced desensitization to CRF in males. Together, these studies identified two aspects of CRFr function, increased cellular signaling and compromised internalization, which render CRF-receptive neurons of females more sensitive to low levels of CRF and less adaptable to high levels of CRF. CRFr dysfunction in females may underlie their increased vulnerability to develop stress-related pathology, particularly that related to increased activity of the LC-norepinephrine system, such as depression or post-traumatic stress disorder.