NdBaScO4: aristotype of a new family of geometric ferroelectrics?

The authors acknowledge the University of St Andrews and the EPSRC (DTG: EP/K503162/1) for a studentship (to CALD). WZ and PSH thank the Welch Foundation (Grant E-1457), NSF DMR-1503573, and the Texas Center for Superconductivity for support. EB thanks the FRS-FNRS for supports and the Consortium des Equipements de Calcul Intensif (CECI), funded by the FRS-FNRS (Grants No. 2.5020.11 and No. 1175545). The research data supporting this publication can be accessed atat http://dx.doi.org/10.17630/197519dd-5b67-49f8-bd50-7f1fb98bec73NdBaScO4 represents the aristotype structure of a new series of -cut layered perovskites; it is suggested that compositional fine-tuning is likely to produce a family of new geometric ferroelectrics, driven primarily by octahedral tilting.PostprintPostprintPeer reviewe

Weak ferromagnetism and internal magnetoelectric effect in LiFeP2_2O7_7

The magnetic, thermodynamic, and pyroelectric properties of LiFeP$_2$O$_7$ single crystals are investigated with emphasis on the magnetoelectric interaction of the electrical polarization with the magnetic order parameter. The magnetic order below T$_N\simeq$ 27 K is found to be a canted antiferromagnet with a weak ferromagnetic component along the $b-$axis. A sharp peak of the pyroelectric current at T$_N$ proves the strong internal magnetoelectric interaction resulting in a sizable polarization decrease at the onset of magnetic order. The magnetoelectric effect in external magnetic fields combines a linear and a quadratic field dependence below T$_N$. Thermal expansion data show a large uniaxial magnetoelastic response and prove the existence of strong spin lattice coupling. LiFeP$_2$O$_7$ is a polar compound with a strong interaction of the magnetic order parameter with the electric polarization and the lattice.Comment: 8 pages, 9 figures, to be published in Phys. Rev.

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb$_{1/2}$Mn$_{1/2}$)O$_3$ as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite $M$Sb$_2$O$_4$; and (3) ferroelectric semiconductors with formula $M_2$P$_2$(S,Se)$_6$. A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties.Comment: 13 pages, 5 figures, 4 table

Bibliografía

Reaction of the anion-deficient, cation-ordered perovskite phase Ba₂YFeO₅ with 80 atm of oxygen pressure at 410 °C results in the formation of the Fe⁴⁺ phase Ba₂YFeO_5.5. The topochemical insertion of oxide ions lifts the inversion symmetry of the centrosymmetric host phase, Ba₂YFeO₅ (space group <i>P</i>2₁/<i>n</i>), to yield a noncentrosymmetric (NCS) phase Ba₂YFeO_5.5 (space group <i>Pb</i>2₁<i>m</i> (No. 26), <i>a</i> = 12.1320(2) Å, <i>b</i> = 6.0606(1) Å, <i>c</i> = 8.0956(1) Å, <i>V</i> = 595.257(2) ų) confirmed by the observation of second-harmonic generation. Dielectric and PUND ferroelectric measurements, however, show no evidence for a switchable ferroelectric polarization, limiting the material to pyroelectric behavior. Magnetization and low-temperature neutron diffraction data indicate that Ba₂YFeO_5.5 undergoes a magnetic transition at 20 K to adopt a state which exhibits a combination of ferromagnetic and antiferromagnetic order. The symmetry breaking from centrosymmetric to polar noncentrosymmetric, which occurs during the topochemical oxidation process is discussed on the basis of induced lattice strain and an electronic instability and represents a new strategy for the preparation of NCS materials that readily incorporate paramagnetic transition metal centers

Remarkable impact of low BiYbO3 doping levels on the local structure and phase transitions of BaTiO3

In-situ Raman spectroscopy shows the simultaneous incorporation of small amounts of Bi3+ and Yb3+ into the lattice of BaTiO3 to break the average symmetry inferred from X-Ray powder diffraction analysis and permittivity measurements. In particular, Bi3+ with a stereochemically active lone-pair of electrons induces severe lattice strain and the coexistence of different local crystal symmetries over a wide temperature range, effectively controlling the physical properties, such as the temperature dependence of the permittivity and the Curie temperature. These results show that compositional gradients based in small variations of these two dopants could successfully explain the enhanced thermal stability of the permittivity in core-shell type ceramics, whereas the lower capacitance of the shell can also cap the maximum permittivity at the Curie temperature

COVID-19 Vaccination and Parent-Reported Symptomatic Child Asthma Prevalence

No abstrac

The role of Zn-OR and Zn-OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics

Analogues of the ligand 2,2'-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)diethanol (CH(3)H(3)L1) are described. Complexation of these analogues, 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (CH(3)HL2), 4-bromo-2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (BrHL2), 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (NO(2)HL2) and 4-methyl-2,6-bis(((2-phenoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (CH(3)HL3) with zinc(II) acetate afforded [Zn-2(CH(3)L2)(CH3COO)(2)](PF6), [Zn-2(NO(2)L2)(CH3COO)(2)](PF6), [Zn-2(BrL2)(CH3COO)(2)](PF6) and [Zn-2(CH(3)L3)(CH3COO)(2)](PF6), in addition to [Zn-4(CH(3)L2)(2)(NO2C6H5OPO3)(2)(H2O)(2)](PF6)(2) and [Zn-4(BrL2)(2)(PO3F)(2)(H2O)(2)](PF6)(2). The complexes were characterized using H-1 and C-13 NMR spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. The complexes contain either a coordinated methyl-(L2 ligands) or phenyl-(L3 ligand) ether, replacing the potentially nucleophilic coordinated alcohol in the previously reported complex [Zn-2(CH(3)HL1)(CH3COO)(H2O)](PF6). Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed them to be competent catalysts with, for example, [Zn-2(CH(3)L2)](+), k(cat) = 5.70 +/- 0.04 x 10(-3) s(-1) (K-m = 20.8 +/- 5.0 mM) and [Zn-2(CH(3)L3)](+), kcat = 3.60 +/- 0.04 x 10(-3) s(-1) (K-m = 18.9 +/- 3.5 mM). Catalytically relevant pK(a)s of 6.7 and 7.7 were observed for the zinc(II) complexes of CH(3)L2(-) and CH(3)L3(-), respectively. Electron donating para-substituents enhance the rate of hydrolysis of BDNPP such that k(cat) p-CH3 > p-Br > p-NO2. Use of a solvent mixture containing H2O18/H2O16 in the reaction with BDNPP showed that for [Zn-2(CH(3)L2)(CH3COO)(2)](PF6) and [Zn-2(NO(2)L2)(CH3COO)(2)](PF6), as well as [Zn-2(CH(3)HL1)(CH3COO)(H2O)](PF6), the O-18 label was incorporated in the product of the hydrolysis suggesting that the nucleophile involved in the hydrolysis reaction was a Zn-OH moiety. The results are discussed with respect to the potential nucleophilic species (coordinated deprotonated alcohol versus coordinated hydroxide)

5,6-Dihydro-1,10-phenanthroline-1,10-diium μ-oxido-bis­[penta­fluoridotantalate(V)]

In the title compound, (C12H12N2)[Ta2F10O], the doubly protonated 5,6-dihydro-1,10-phenantroline-1,10-diium cation is located on a twofold rotation axis, whereas the isolated [Ta2OF10]2− dianion has -1 symmetry. In the so far unknown dianion, the symmetry-related TaV atoms are octa­hedrally coordinated by five F atoms and a bridging O atom, the latter being located on an inversion centre. The two pyridine rings in the cation make a dihedral angle of 22.8 (4)°. The cations and dianions are arranged in layers parallel to (100) and are connected through N—H⋯F and C—H⋯F hydrogen-bonding inter­actions into a three-dimensional structure

Conflicting measures of hospital quality: Ratings from “Hospital Compare” versus “Best Hospitals”

BACKGROUND In April 2005 the Centers for Medicare and Medicaid Services launched “Hospital Compare,” the first government-sponsored hospital quality scorecard. We compared the ranking of U.S. News and World Report 's “Best Hospitals” with Hospital Compare performance ratings. METHODS We examined Hospital Compare scores for core measures related to care for acute myocardial infarction (AMI), congestive heart failure (CHF), and community-acquired pneumonia (CAP). We calculated composite scores for the disease-specific sets of core measures and a composite combined score for the 14 core measures (across 3 diseases) and determined national score quartile cut points for each set. We then characterized the quartile distribution of Hospital Compare scores for the Best Hospitals for care of cardiac conditions and respiratory disorders in each year, as well as for the Best Hospital “Honor Roll” institutions. RESULTS AMI scores were available for 2165 hospitals, CHF scores for 3130, and CAP scores for 3462. In both 2004 and 2005, fewer than 50% of the Best Hospitals for cardiac care rated in the top quartile of Hospital Compare scores for AMI and CHF. Among the Best Hospitals for care of respiratory disorders, fewer than 15% scored in the top Hospital Compare quartile for CAP. Among Honor Roll institutions, only 5 (of 14 hospitals in 2004; of 16 in 2005) ranked in the top quartile for the combined core measure score. CONCLUSIONS Hospital Compare scores are frequently discordant with Best Hospital rankings, which is likely attributable to the markedly different methods each rating approach employs. Such discordance between major quality rating systems paints a conflicting picture of institutional performance for the public to interpret. Journal of Hospital Medicine 2007;2:128–134. © 2007 Society of Hospital Medicine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56098/1/176_ftp.pd

Cation Exchange as a Route to Introduce Magnetism to Hybrid-Improper Polar Phases

The pseudo Ruddlesden–Popper phase Li2CaTa2O7 is converted to ZnCaTa2O7, FeCaTa2O7, or CoCaTa2O7 by reaction with the corresponding transition-metal dichloride. Diffraction data reveal that ZnCaTa2O7 adopts a polar crystal structure (P2cm) with the Zn2+cations ordered into stripes within the interlayer coordination sites, and the TaO6 units adopt an a – b – c +/–(a – b –)c + tilting pattern. In contrast, FeCaTa2O7 and CoCaTa2O7 adopt polar structures (P21 nm) with the transition-metal cations ordered in a checkerboard pattern within the interlayer coordination sites, and the TaO6 units adopt an a – b – c +/ b – a – c + tilting pattern. The different polar structures adopted are rationalized on the basis of the size of the interlayer transition-metal cation. On cooling, FeCaTa2O7 (T N = 40 K) and CoCaTa2O7 (T N = 25 K) adopt antiferromagnetically ordered states with spins aligned parallel to the crystallographic stacking axis and arranged in a G-type manner. Close inspection of the NPD data collected from FeCaTa2O7 at low temperature reveals a diffuse component to the magnetic scattering, which, in combination with magnetization data, suggest a glassy component to the low-temperature magnetic state. Neither FeCaTa2O7 nor CoCaTa2O7 shows significant lattice parameter anomalies around their respective Néel temperatures, in contrast to the previously reported manganese analogue MnCaTa2O7