Direct observation of the ground state of a 1/3 quantum magnetization plateau in SrMn3_3P4_4O14_{14} using neutron diffraction measurements

We can directly investigate the ground state in magnetization-plateau fields (plateau ground state) using neutron diffraction measurements. We performed neutron diffraction measurements on the spin-5/2 trimer substance SrMn$_3$P$_4$O$_{14}$ in magnetization-plateau fields. The integrated intensities of magnetic reflections calculated using an expectation value of each spin in a plateau ground state of an isolated-trimer model agree well with those obtained experimentally in the magnetization-plateau fields. We succeeded in direct observation of a plateau ground state in SrMn$_3$P$_4$O$_{14}$

Spiral magnetic structure in spin-5/2 frustrated trimerized chains in SrMn3P4O14

We study a spin-5/2 antiferromagnetic trimerized chain substance SrMn3P4O14 using neutron powder diffraction experiments. The coplanar spiral magnetic structure appears below T_N1 = 2.2(1) K. Values of several magnetic structure parameters change rapidly at T_N2 = 1.75(5) K, indicating another phase transition, although the magnetic structures above and below T_N2 are the qualitatively same. The spiral magnetic structure can be explained by frustration between nearest-neighbor and next-nearest-neighbor exchange interactions in the trimerized chains.Comment: submitted to Phys. Rev.

Regulation of NDVI and ET negative responses to increased atmospheric vapor pressure deficit by water availability in global drylands

Atmospheric vapor pressure deficit (VPD, indicative of atmospheric water conditions) has been identified as a major driver of global vegetation dynamics. Drylands, including deserts, temperate grasslands, savannas, and dry forests, are more sensitive to water conditions and affect carbon, nitrogen, and water cycles. However, our knowledge is limited on the way increasing VPD affects vegetation growth and evapotranspiration (ET) in global drylands. In this study, we used long-term satellite datasets combined with multiple statistical analyses to examine the relationship between the satellite-derived normalized difference vegetation index (NDVI), a proxy for vegetation growth, and ET to VPD across global drylands. We found that significant decreases in NDVI and ET predominantly influenced the NDVI (RVPD − NDVI) and ET (RVPD − ET) responses to VPD in both the savannas and dry forests of South American, African, and Australian savannas and dry forests, as well as in temperate grasslands (e.g., Eurasian steppes and American prairies). Notably, more than 60% of global drylands exhibited significantly negative RVPD − NDVI and RVPD − ET values. In contrast, the percentage of significantly negative RVPD − NDVI and RVPD − ET decreased to <10% in cold drylands (>60° N). In predominantly warm drylands (60° N~60° S), negative VPD effects were significantly and positively regulated by soil water availability, as determined by multiple linear regression models. However, these significant regulatory effects were not observed in cold drylands. Moving-window analyses further revealed that temporal changes in RVPD − NDVI and RVPD − ET were positively correlated with changes in the Standardized Precipitation Evapotranspiration Index (SPEI). In warm drylands, areas with increasing RVPD − NDVI and RVPD − ET over time showed an increasing trend in the SPEI, whereas areas with a decreasing SPEI showed a negative trend in RVPD − NDVI and RVPD − ET values over time. Given the increasing atmospheric dryness due to climate change, this study highlighted the importance of re-evaluating the representation of the role of water availability in driving the response of the carbon-water cycle to increased VPD across global drylands

Modeling and Analysis of the Influence of an Edge Filter on the Combining Efficiency and Beam Quality of a 10-kW-Class Spectral Beam-Combining System

Filter-based spectral beam combining (FSBC) is a promising power-scaling concept for high-power, broad-linewidth fiber lasers, as it relaxes the requirements for linewidth control and also the sizes of the individual beams. As the combining element in the FSBC system, the steep-edge filter plays a major role in achievement of the combining efficiency and the beam quality. In this case, we combine the uncorrelated surface roughness model and the combining efficiency model, and we conduct a comprehensive analysis of the effects of surface roughness, thickness error, and incident angle on the filter’s optical properties and the combining efficiency, in order to determine the optimal configuration for the laser beam-combining system. The simulation results show a good agreement with the measured ones. Meanwhile, through the adoption of the angular spectrum theory, this paper has also conducted a preliminary analysis of the influence of the combining elements on the quality of the combined beam, and some theoretical instructions on the future design of the spectral beam-combining system are provided

Observation of the Sixth Polymorph of BiB₃O₆: In Situ High-Pressure Raman Spectroscopy and Synchrotron X‑ray Diffraction Studies on the β‑Polymorph

β-BiB₃O₆ was compressed in a diamond anvil cell at room temperature and studied using a combinstion of in situ high-pressure Raman scattering and angle-dispersive synchrotron X-ray diffraction. The results reveal that β-BiB₃O₆ retains its structure below 9.0 GPa and undergoes a structural phase transition that starts at ∼11.5 GPa and finishes at ∼18.5 GPa. No other phase transition occurred with increasing pressure up to ∼46 GPa. It was also found that the high-pressure phase is different from the already-reported five polymorphs of BiB₃O₆. Therefore, the new phase is denoted as ζ-BiB₃O₆, which could be indexed by an orthorhombic unit cell (<i>a</i> ≈ 12.5 Å, <i>b</i> ≈ 6.7 Å, <i>c</i> ≈ 4.0 Å) from the powder XRD pattern collected at 22.2 GPa. Moreover, ζ-BiB₃O₆ can be quenched to ambient conditions. The investigation of the pressure dependence of the lattice parameters reveals that both β-BiB₃O₆ and ζ-BiB₃O₆ exhibit a large amount of crystallographic anisotropy. An unusual expansion of the <i>c</i>-axis of ζ-BiB₃O₆ was observed. Assignments for the Raman spectra of β-BiB₃O₆, γ-BiB₃O₆, and δ-BiB₃O₆ under ambient conditions were also performed. Currently, we cannot solve the crystal structure of ζ-BiB₃O₆ but give some speculations based on its relationship with β-BiB₃O₆

Chemical Substitution-Induced and Competitive Formation of 6H and 3C Perovskite Structures in Ba_3–<i>x</i>Sr_<i>x</i>ZnSb₂O₉: The Coexistence of Two Perovskites in 0.3 ≤ <i>x</i> ≤ 1.0

6H and 3C perovskites are important prototype structures in materials science. We systemically studied the structural evolution induced by the Sr²⁺-to-Ba²⁺ substitution to the parent 6H perovskite Ba₃ZnSb₂O₉. The 6H perovskite is only stable in the narrow range of <i>x</i> ≤ 0.2, which attributes to the impressibility of [Sb₂O₉]. The preference of 90° Sb–O–Sb connection and the strong Sb⁵⁺-Sb⁵⁺ electrostatic repulsion in [Sb₂O₉] are competitive factors to stabilize or destabilize the 6H structure when chemical pressure was introduced by Sr²⁺ incorporation. Therefore, in the following, a wide two-phase region containing 1:2 ordered 6H–Ba_2.8Sr_0.2ZnSb₂O₉ and rock-salt ordered 3C–Ba₂SrZnSb₂O₉ was observed (0.3 ≤ <i>x</i> ≤ 1.0). In the final, the successive symmetry descending was established from cubic (<i>Fm</i>3̅<i>m</i>, 1.3 ≤ <i>x</i> ≤ 1.8) to tetragonal (<i>I</i>4/<i>m</i>, 2.0 ≤ <i>x</i> ≤ 2.4), and finally to monoclinic (<i>I</i>2/<i>m</i>, 2.6 ≤ <i>x</i> ≤ 3.0). Here we proved that the electronic configurations of B-site cations, with either empty, partially, or fully filled d-shell, would also affect the structure stabilization, through the orientation preference of the B–O covalent bonding. Our investigation gives a deeper understanding of the factors to the competitive formation of perovskite structures, facilitating the fine manipulation on their physical properties

ZnGa_2–<i>x</i>In_<i>x</i>S₄ (0 ≤ <i>x</i> ≤ 0.4) and Zn_{1–2<i>y</i>}(CuGa)_<i>y</i>Ga_1.7In_0.3S₄ (0.1 ≤ <i>y</i> ≤ 0.2): Optimize Visible Light Photocatalytic H₂ Evolution by Fine Modulation of Band Structures

Band structure engineering is an efficient technique to develop desired semiconductor photocatalysts, which was usually carried out through isovalent or aliovalent ionic substitutions. Starting from a UV-activated catalyst ZnGa₂S₄, we successfully exploited good visible light photocatalysts for H₂ evolution by In³⁺-to-Ga³⁺ and (Cu⁺/Ga³⁺)-to-Zn²⁺ substitutions. First, the bandgap of ZnGa_2–<i>x</i>­In_<i>x</i>S₄ (0 ≤ <i>x</i> ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction band position. Second, Zn_{1–2<i>y</i>}(CuGa)_<i>y</i>­Ga_1.7In_0.3S₄ (<i>y</i> = 0.1, 0.15, 0.2) provided a further and significant red-shift of the photon absorption to ∼500 nm by raising the valence band maximum and barely losing the overpotential to water reduction. Zn_0.7Cu_0.15­Ga_1.85In_0.3S₄ possessed the highest H₂ evolution rate under pure visible light irradiation using S^2– and SO₃^2– as sacrificial reagents (386 μmol/h/g for the noble-metal-free sample and 629 μmol/h/g for the one loaded with 0.5 wt % Ru), while the binary hosts ZnGa₂S₄ and ZnIn₂S₄ (synthesized using the same procedure) show 0 and 27.9 μmol/h/g, respectively. The optimal apparent quantum yield reached to 7.9% at 500 nm by tuning the composition to Zn_0.6Cu_0.2­Ga_1.9In_0.3S₄ (loaded with 0.5 wt % Ru)