High pressure synthesis of FeO-ZnO solid solutions with rock salt structure: in situ X-ray diffraction studies

X-ray diffraction with synchrotron radiation has been used for the first time to study chemical interaction in the FeO-ZnO system at 4.8 GPa and temperatures up to 1300 K. Above 750 K, the chemical reaction between FeO and ZnO has been observed that resulted in the formation of rock salt (rs) Fe1-xZnxO solid solutions (0.3 \leq x \leq 0.85). The lattice parameters of these solid solutions have been in situ measured as a function of temperature under pressure, and corresponding thermal expansion coefficients have been calculated.Comment: 9 pages, 2 figures, 1 tabl

The phase diagram of NiSi under the conditions of small planetary interiors

The phase diagram of NiSi has been determined using in situ synchrotron X-ray powder diffraction multi-anvil experiments to 19 GPa, with further preliminary results in the laser-heated diamond cell reported to 60 GPa. The low-pressure MnP-structured phase transforms to two different high-pressure phases depending on the temperature: the ε-FeSi structure is stable at temperatures above ∼1100 K and a previously reported distorted-CuTi structure (with Pmmn symmetry) is stable at lower temperature. The invariant point is located at 12.8 ± 0.2 GPa and 1100 ± 20 K. At higher pressures, ε -FeSi-structured NiSi transforms to the CsCl structure with CsCl-NiSi as the liquidus phase above 30 GPa. The Clapeyron slope of this transition is -67 MPa/K. The phase boundary between the ε -FeSi and Pmmn structured phases is nearly pressure independent implying there will be a second sub-solidus invariant point between CsCl, ε -FeSi and Pmmn structures at higher pressure than attained in this study. In addition to these stable phases, the MnP structure was observed to spontaneously transform at room temperature to a new orthorhombic structure (also with Pnma symmetry) which had been detailed in previous ab initio simulations. This new phase of NiSi is shown here to be metastable

Hooked on switch: strain-managed cooperative Jahn-Teller effect in Li0.95Mn2.05O4Li_{ 0.95}Mn_{2.05}O_{4} spinel

Compression and heating of Li0.95Mn2.05O4 induce a unique three-way switch. We demonstrate the possibility of tuning of the structural properties and the induction of phase transitions by changing the external pressure and temperature, and hence changing the lattice strain.</p

Reduced dementia incidence after varicella zoster vaccination in Wales 2013–2020

Abstract Introduction Chronic infection with herpes viruses is a potential contributing factor to the development of dementia. The introduction of nationwide shingles (varicella zoster) vaccination in Wales might therefore be associated with reduced incident dementia. Methods We analyzed the association of shingles vaccination with incident dementia in Wales between 2013 and 2020 using retrospectively collected national health data. Results Vaccinated individuals were at reduced risk of dementia (adjusted hazard ratio: 0.72; 95% confidence interval: 0.69 to 0.75). The association was not modified by a reduction in shingles diagnosis and was stronger for vascular dementia than for Alzheimer's disease. Vaccination was also associated with a reduction in several other diseases and all‐cause mortality. Discussion Our study shows a clear association of shingles vaccination with reduced dementia, consistent with other observational cohort studies. The association may reflect selection bias with people choosing to be vaccinated having a higher healthy life expectancy

Mn₃O₄ under High Pressure and Temperature: Thermal Stability, Polymorphism, and Elastic Properties

We report results of in situ synchrotron X-ray diffraction studies of hausmannite up to 7.2 GPa and 1273 K. The Mn₃O₄ tetragonal spinel is found to transform to a 9.6% denser polymorph of the CaMn₂O₄-type structure at 7.2 GPa and 673 K, under milder conditions than those of any transformations to postspinel phase described so far. Upon heating at high pressure, the Mn₃O₄ phase undergoes decomposition and finally disappears in favor of MnO at temperatures above 1073 K. A fit of the pressure dependence of the volume of tetragonal phase to the Birch–Murnaghan equation of state yields the bulk modulus, <i>K</i>₀, of 132.6 ± 3.1 GPa if the first pressure derivative of the bulk modulus is fixed to 4, and <i>K</i>₀, of 102 ± 10 GPa for <i>K</i>₀′ refined to 18.1 ± 5.6. Nonlinear compression behavior is observed for both crystallographic axes, with the <i>c</i> axis being more compressible than the <i>a</i> axis. Axial ratios in CaMn₂O₄-type Mn₃O₄ with temperature are also estimated. Surprisingly, the lattice distortion of the marokite-like phase is not preserved upon releasing pressure and temperature to ambient conditions

Effect of the microstructure of graphitic boron nitride on the kinetics of the formation of boron nitride high-pressure phases

Three types of hexagonal boron nitride (h-BN) with graphitic crystal structure having different microstructures were subjected to high pressures (HP) and high temperatures (HT), and the kinetics of the phase transitions to the sp$^3$-hybridized phases (w-BN, c-BN) was studied using in situ synchrotron diffraction. The analysis of the phase transformation kinetics revealed the transformation paths and activation energies E$_a$ of the transformation of h-BN to the high-pressure forms of BN for different microstructures of h-BN. Defect-poor h-BN transforms to metastable wurtzitic BN (w-BN) with E$_a$ ≈ 0.3 eV/at. Defect-rich forms of h-BN transform directly to c-BN, but with a higher activation energy. It was observed that the turbostratic disorder in h-BN retards the phase transition as compared to h-BN containing corrugated basal planes and a low degree of turbostracity. The experimental results are discussed in view of the microstructure changes during the HP/HT treatment and compared to available theoretical phase transition models