Electronic, Vibrational, and Structural Properties of the Natural Mineral Ferberite (FeWO4): A High-Pressure Study.

This paper reports an experimental high-pressure study of natural mineral ferberite (FeWO4) up to 20 GPa using diamond-anvil cells. First-principles calculations have been used to support and complement the results of the experimental techniques. X-ray diffraction patterns show that FeWO4 crystallizes in the wolframite structure at ambient pressure and is stable over a wide pressure range, as is the case for other wolframite AWO4 (A = Mg, Mn, Co, Ni, Zn, or Cd) compounds. No structural phase transitions were observed for FeWO4, in the pressure range investigated. The bulk modulus (B0 = 136(3) GPa) obtained from the equation of state is very close to the recently reported value for CoWO4 (131(3) GPa). According to our optical absorption measurements, FeWO4 has an indirect band gap that decreases from 2.00(5) eV at ambient pressure to 1.56(5) eV at 16 GPa. First-principles simulations yield three infrared-active phonons, which soften with pressure, in contrast to the Raman-active phonons. These results agree with Raman spectroscopy experiments on FeWO4 and are similar to those previously reported for MgWO4. Our results on FeWO4 are also compared to previous results on other wolframite-type compounds.

2D Cu(I)-I Coordination Polymer with Smart Optoelectronic Properties and Photocatalytic Activity as a Versatile Multifunctional Material.

This work presents two isostructural Cu(I)-I 2-fluoropyrazine (Fpyz) luminescent and semiconducting 2D coordination polymers (CPs). Hydrothermal synthesis allows the growth of P-1 space group single crystals, whereas solvent-free synthesis produces polycrystals. Via recrystallization in acetonitrile, P21 space group single crystals are obtained. Both show a reversible luminescent response to temperature and pressure. Structure determination by single-crystal X-ray diffraction at 200 and 100 K allows us to understand their response as a function of temperature. Applying hydrostatic/uniaxial pressure or grinding also generates significant variations in their emission. The high structural flexibility of the Cu(I)-I chain is significantly linked to the corresponding alterations in structure. Remarkably, pressure can increase the conductivity by up to 3 orders of magnitude. Variations in resistivity are consistent with changes in the band gap energy. The experimental results are in agreement with the DFT calculations. These properties may allow the use of these CPs as optical pressure or temperature sensors. In addition, their behavior as a heterogeneous photocatalyst of persistent organic dyes has also been investigated.

Reassigning the Pressure-Induced Phase Transitions of Methylammonium Lead Bromide Perovskite.

The high-pressure crystal structure evolution of CH3NH3PbBr3 (MAPbBr3) perovskite has been investigated by single-crystal X-ray diffraction and synchrotron-based powder X-ray diffraction. Single-crystal X-ray diffraction reveals that the crystal structure of MAPbBr3 undergoes two phase transitions following the space-group sequence: Pm3̅m → Im3̅ → Pmn21, unveiling the occurrence of a nonpolar/polar transition (Im3̅ → Pmn21). The transitions take place at around 0.8 and 1.8 GPa, respectively. This result contradicts the previously reported phase transition sequence: Pm3̅m → Im3̅ →Pnma. In this work, the crystal structures of each of the three phases are determined from single-crystal X-ray diffraction analysis, which is later supported by Rietveld refinement of powder X-ray diffraction patterns. The pressure dependence of the crystal lattice parameters and unit-cell volumes are determined from the two aforementioned techniques, as well as the bulk moduli for each phase. The bandgap behavior of MAPbBr3 has been studied up to around 4 GPa, by means of single-crystal optical absorption experiments. The evolution of the bandgap has been well explained using the pressure dependence of the Pb-Br bond distance and Pb-Br-Pb angles as determined from single-crystal X-ray diffraction experiments.

Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting ß-Cu2V2O7.

The understanding of the interplay between crystal structure and electronic structure in semiconductor materials is of great importance due to their potential technological applications. Pressure is an ideal external control parameter to tune the crystal structures of semiconductor materials in order to investigate their emergent piezo-electrical and optical properties. Accordingly, we investigate here the high-pressure behavior of the semiconducting antiferromagnetic material ß-Cu2V2O7, finding it undergoes a pressure-induced phase transition to γ-Cu2V2O7 below 4000 atm. The pressure-induced structural and electronic evolutions are investigated by single-crystal X-ray diffraction, absorption spectroscopy and ab initio density functional theory calculations. ß-Cu2V2O7 has previously been suggested as a promising photocatalyst for water splitting. Now, these new results suggest that ß-Cu2V2O7 could also be of interest with regards to barocaloric effects, due to the low phase -transition pressure, in particular because it is a multiferroic material. Moreover, the phase transition involves an electronic band gap decrease of approximately 0.2 eV (from 1.93 to 1.75 eV) and a large structural volume collapse of approximately 7%.

Reactivity of Hydrogen-Helium and Hydrogen-Nitrogen Mixtures at High Pressures.

Through a series of Raman spectroscopy studies, we investigate the behavior of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across a wide range of concentrations. We find that there is no evidence of chemical association or increased miscibility of hydrogen and helium in the solid state up to pressures of 250 GPa at 300 K. In contrast, we observe the formation of concentration-dependent N_{2}-H_{2} van der Waals solids, which react to form N-H bonded compounds above 50 GPa. Through this combined study, we can demonstrate that the recently reported chemical association of H_{2}-He can be attributed to significant N_{2} contamination and subsequent formation of N_{2}-H_{2} compounds.

Dynamical Torque in CoxFe3-xO4 Nanocube Thin Films Characterized by Femtosecond Magneto-Optics: A π-Shift Control of the Magnetization Precession.

For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles.

High-Pressure Behavior of Ca2SnO4, Sr2SnO4, and Zn2SnO4.

The pressure-induced structural evolution of Ca2SnO4, Sr2SnO4, and Zn2SnO4 has been characterized by powder X-ray diffraction up to 20 GPa using the ALBA synchrotron radiation source and density functional theory calculations. No phase transition was observed in Ca2SnO4 and Zn2SnO4 in the investigated pressure range. The observation in Zn2SnO4 solves contradictions existing in the literature. In contrast, a phase transition was observed in Sr2SnO4 at a pressure of 9.09 GPa. The transition was characterized as from the ambient-condition tetragonal polymorph (space group I4/mmm) to the low-temperature tetragonal polymorph (space group P42/ncm). The linear compressibility of crystallographic axes and room-temperature pressure-volume equation of state are reported for the three compounds studied. Calculated elastic constants and moduli are also reported as well as a systematic discussion of the high-pressure behavior and bulk modulus of M2SnO4 stannates.

PbV2O6 under compression: near zero-linear compressibility and pressure-induced change in vanadium coordination.

This study presents evidence that lead metavanadate, PbV2O6, is a material with zero-linear compressibility, which maintains its crystal size in one crystallographic direction even under external pressures of up to 20 GPa. The orthorhombic polymorph of PbV2O6 (space group Pnma) was studied up to 20 GPa using synchrotron powder X-ray diffraction, Raman spectroscopy, and density-functional theory simulations to investigate its structural and vibrational evolution under compression. Up to this pressure we find no evidence of any structural phase transitions by any diagnostic technique, however, a progressive transformation of the coordination polyhedron of vanadium atoms is revealed which results in the zero-linear compressibility. High-pressure Raman experiments enabled the identification and symmetry assignation of all 54 zone-centre Raman-active modes as well as the calculation of their respective pressure coefficients. Three independent high-pressure powder X-ray diffraction experiments were performed using different pressure-transmitting media (Ne, 4 : 1 methanol-ethanol mixture, and silicone oil). The results show a high anisotropic behaviour in the linear compressibility of the crystallographic axes. The PbV2O6 bulk modulus of 86.1(9) GPa was determined using a third-order Birch-Murnaghan equation of state. The experimental results are supported by ab initio density-functional theory calculations, which provide vibrational patterns, unit-cell parameters, and atomic positions. These calculations also reveal that, unlike MgV2O6 and ZnV2O6, the band gap of PbV2O6 closes with pressure at a rate of -54 meV GPa-1 due to the contribution of the Pb 6s orbital to the top of the valence band.

Mapping of allied health service capacity for maternity and neonatal services in the southern Queensland health service district.

OBJECTIVE: Allied health professionals (AHPs) in maternity and neonatology services are essential for quality care and outcomes, reflected in the minimum service delivery requirements in the Queensland Health clinical services capability framework (CSCF). However, allied health (AH) capacity across the Southern Queensland Health Service Districts (SQHSD) is not known. The aim of this project was to redress this knowledge gap to inform ongoing service planning and delivery. METHODS: Maternity and neonatal AH clinicians in all birthing facilities in SQHSD were surveyed between October and December 2011 to investigate AHP staffing, practices and models of care. The professions surveyed included dietitians, occupational therapists, physiotherapists, psychologists, social workers and speech pathologists. Results were grouped per question, with stratification by CSCF and/or profession. RESULTS: Fifty-five valid surveys from the 16 facilities were received. All professions were represented. Gaps in maternity AH services were identified. Awareness and use of evidence-based practices were more likely to be reported where higher full-time equivalents (FTE) were allocated. CONCLUSION: Very low staffing levels have been recorded in all Maternity and Neonatology Services AHPs in the SQHSD. Gaps exist between actual and recommended CSCF staffing standards across all levels and professions. The results indicate that profession-specific support networks for AHPs have positive effects in the spreading of information, and continued promotion, support and involvement in these profession-specific networks is suggested for all facilities.

Pressure-Induced Phase Transition versus Amorphization in Hybrid Methylammonium Lead Bromide Perovskite.

The crystal structure of the CH3NH3PbBr3 perovskite has been investigated under high-pressure conditions by synchrotron-based powder X-ray diffraction. We found that after the previously reported phase transitions in CH3NH3PbBr3 (Pm3̅m→Im3̅→Pmn21), which occur below 2 GPa, there is a third transition to a crystalline phase at 4.6 GPa. This transition is reported here for the first time contradicting previous studies, which reported amorphization of CH3NH3PbBr3 between 2.3 and 4.6 GPa. Our X-ray diffraction measurements show that CH3NH3PbBr3 remains crystalline up to at least 7.6 GPa, the highest pressure covered by experiments. The new high-pressure phase is also described by the space group Pmn21; however, the transition involves abrupt changes in the unit-cell parameters and a 3% decrease of the unit-cell volume. Our conclusions are confirmed by optical-absorption experiments, by visual observations, and by the fact that pressure-induced changes up to 10 GPa are reversible. The optical studies also allow for the determination of the pressure dependence of the band-gap energy, which is discussed using the structural information obtained from X-ray diffraction.

Characterization of the high-pressure and high-temperature phase diagram and equation of state of chromium.

The high-pressure and high-temperature phase diagram of chromium has been investigated both experimentally (in situ), using a laser-heated diamond-anvil cell technique coupled with synchrotron powder X-ray diffraction, and theoretically, using ab initio density-functional theory simulations. In the pressure-temperature range covered experimentally (up to 90 GPa and 4500 K, respectively) only the solid body-centred-cubic and liquid phases of chromium have been observed. Experiments and computer calculations give melting curves in agreement with each other that can both be described by the Simon-Glatzel equation [Formula: see text]. In addition, a quasi-hydrostatic equation of state at ambient temperature has been experimentally characterized up to 131 GPa and compared with the present simulations. Both methods give very similar third-order Birch-Murnaghan equations of state with bulk moduli of 182-185 GPa and respective pressure derivatives of 4.74-5.15. According to the present calculations, the obtained melting curve and equation of state are valid up to at least 815 GPa, at which pressure the melting temperature is 9310 K. Finally, from the obtained results, it was possible to determine a thermal equation of state of chromium valid up to 65 GPa and 2100 K.

Simple New Method for the Preparation of La(IO3)3 Nanoparticles.

We present a cost- and time-efficient method for the controlled preparation of single phase La(IO3)3 nanoparticles via a simple soft-chemical route, which takes a matter of hours, thereby providing an alternative to the common hydrothermal method, which takes days. Nanoparticles of pure α-La(IO3)3 and pure δ-La(IO3)3 were synthesised via the new method depending on the source of iodate ions, thereby demonstrating the versatility of the synthesis route. The crystal structure, nanoparticle size-dispersal, and chemical composition were characterised via angle- and energy-dispersive powder X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy.

Unusually complex phase of dense nitrogen at extreme conditions.

Nitrogen exhibits an exceptional polymorphism under extreme conditions, making it unique amongst the elemental diatomics and a valuable testing system for experiment-theory comparison. Despite attracting considerable attention, the structures of many high-pressure nitrogen phases still require unambiguous determination. Here, we report the structure of the elusive high-pressure high-temperature polymorph ι-N2 at 56 GPa and ambient temperature, determined by single crystal X-ray diffraction, and investigate its properties using ab initio simulations. We find that ι-N2 is characterised by an extraordinarily large unit cell containing 48 N2 molecules. Geometry optimisation favours the experimentally determined structure and density functional theory calculations find ι-N2 to have the lowest enthalpy of the molecular nitrogen polymorphs that exist between 30 and 60 GPa. The results demonstrate that very complex structures, similar to those previously only observed in metallic elements, can become energetically favourable in molecular systems at extreme pressures and temperatures.

Formation of xenon-nitrogen compounds at high pressure.

Molecular nitrogen exhibits one of the strongest known interatomic bonds, while xenon possesses a closed-shell electronic structure: a direct consequence of which renders both chemically unreactive. Through a series of optical spectroscopy and x-ray diffraction experiments, we demonstrate the formation of a novel van der Waals compound formed from binary Xe-N2 mixtures at pressures as low as 5 GPa. At 300 K and 5 GPa Xe(N2)2-I is synthesised, and if further compressed, undergoes a transition to a tetragonal Xe(N2)2-II phase at 14 GPa; this phase appears to be unexpectedly stable at least up to 180 GPa even after heating to above 2000 K. Raman spectroscopy measurements indicate a distinct weakening of the intramolecular bond of the nitrogen molecule above 60 GPa, while transmission measurements in the visible and mid-infrared regime suggest the metallisation of the compound at ~100 GPa.

Prospective testing of the Brisbane Postnatal Depression Index.

BACKGROUND: Over 50 percent of women have one or more risk factors for postnatal depression during pregnancy or in the perinatal period, but only 10 to 15 percent become clinically depressed. The objective of this study was to prospectively test the Brisbane Postnatal Depression Index (referred to here as Index), to validate a theoretical index that was developed earlier, and to establish whether the index could be introduced as a clinically useful method to detect women who may be at risk for developing postnatal depression. METHODS: Antenatally, women were asked about social support and about personal and family history of mental illness, including postnatal depression. Responses were scored according to predefined ratings on the Index. In the postnatal wards, 353 women were recruited and their scores for "blues," social support, feelings about the baby, and satisfaction with the birth process were added. Sixteen weeks after hospital discharge, women were asked to complete the Edinburgh Postnatal Depression Scale. The Brisbane Index was validated by the number of women scoring more than 12 on the Edinburgh Postnatal Depression Scale at 16 weeks postpartum who were correctly predicted by a score of more than 6 on the Index. Sensitivity, specificity, positive predictive value, and negative predictive value for the Index, using >6 as a cutoff point, were calculated. "Ease of use" was assessed informally with participants and staff responsible for administration and scoring the instrument. RESULTS: Compared with results from the derivation study, prospective testing of the index showed an improvement in sensitivity from 36.3 to 47.5 percent and a small decrease in specificity, but no improvement on the positive predictive value from 39.8 to 39.6 percent. CONCLUSION: The Brisbane Postnatal Depression Index was validated in a prospective sample, but its sensitivity and specificity require improvement before introduction as a measure of prediction.