Pressure-induced phase transition in α- and ß-BiNbO4.

BiNbO4 has attracted a great deal of interest due to its excellent photocatalytic activities. Besides, it possesses rich polymorphism. Here, the structural stability and structural evolution of orthorhombic α- and triclinic ß-BiNbO4 were investigated via in situ X-ray diffraction patterns and Raman spectra up to 46.7 GPa. Upon compression, both BiNbO4 samples become unstable. α-BiNbO4 transformed into the monoclinic C2/c structure at 10.3 GPa, while ß-BiNbO4 possessed one P1̄-to-P1 isostructural phase transition around 12.7 GPa, and for the first time the crystal structure of each high pressure phase was identified. Both high pressure structures remained stable without obvious symmetry changes during compression to 46.7 GPa. In addition, both phase transitions were reversible upon decompression. These results provide insights to understand pressure-induced reversible phase transition in ABO4 compounds with polymorphism.

Hydrogen-bond enhancement triggered structural evolution and band gap engineering of hybrid perovskite (C6H5CH2NH3)2PbI4 under high pressure.

Hybrid organic-inorganic perovskites (HOIPs) have gained substantial attention due to their excellent photovoltaic and optoelectronic properties. Herein, we comprehensively investigate a typical two-dimensional (2D) hybrid perovskite (C6H5CH2NH3)2PbI4 to track its structural and band gap evolution applied by the maximum pressure of 27.2 GPa. Remarkably, an unprecedented band gap narrowing down to the Shockley-Queisser limit is observed upon compression to 20.1 GPa. Two phase transitions have been observed during this process: the ambient Pbca phase converts into the Pccn phase at 4.6 GPa and then undergoes an isostructural phase transition at 7.7 GPa. The Fourier Transform Infrared (FTIR) spectroscopy reveals that pressure-enhanced hydrogen bonding plays an important role in structural modifications and band gap variations. This work not only enables high pressure as a clean tool to tune the structure and band gap of hybrid perovskite, but also maps a pioneering route towards realizing ideal photovoltaic materials-by-design.

Disorder-order structural transition of single crystal hydrogen chloride under high pressure-temperature.

Hydrogen chloride (HCl) is the simplest hydrogen-bonded molecule and has attracted a great deal of attention owing to its interesting structural changes triggered by pressure or temperature. The structural properties of solid HCl have been investigated by Brillouin scattering in the pressure range of 0-20 GPa under high temperature, combined with external heating in a diamond anvil cell. Three elastic constants and two moduli of the single crystal sample were observed at high pressure-temperature and each of them grows monotonously with pressure along a separate isotherm. The pressure dependence of elastic anisotropy proves that the disorder-order transition pressures are 4.5 GPa, 5.4 GPa and 8.8 GPa for the 300 K, 390 K and 470 K isotherms, respectively. The current work discovered the disorder-order structural transition in HCl and extended its phase diagram to the high pressure-temperature range, also providing a new insight into other simple hydrogen-bonded molecular compounds.

New Metallic Ordered Phase of Perovskite CsPbI3 under Pressure.

Pressure-induced electronic structure transition from insulating phase to metal state is a potential new paradigm for halide perovskites. The metallization based on these materials may afford a novel motif toward realizing new electronic properties even superconductivity phenomenon. Herein, how static compression modulates the crystal and electronic structure of typical perovskite semiconductors cesium lead iodine (CsPbI3) by both experimental and theoretical studies is reported. The comprehensive studies discover the insulator-metal transition of CsPbI3 at 39.3 GPa, and reveal the key information behind the electronic transition. The perovskite's precise structural evolution is tracked upon compression, from orthorhombic Pnma phase to monoclinic C2/m structure before the metallic transition. More interestingly, the C2/m phase has the most distorted octahedra and the shortest Pb-I bond length relative to the average bond length that is ever reported in a halide perovskite structure. The electronic transition stems from the structural changes accompanied by the anomalously self-distorted octahedra. These studies show that pressure can significantly alter the structural and electronic properties of these technologically important perovskites.

[Response of growth and photosynthetic characteristics of Polygonatum cyrtonema to shading conditions].

The purpose of this experiment was to study the effects of different shading conditions on the growth,physiological characteristics and biomass allocation of Polygonatum cyrtonema,which offered a theoretical basis for its cultivation.Different light environments(100%,80%,60% and 35% light transmittance) were simulated with shading treatments.Growth and photosynthetic indexes of P.cyrtonema were measured and the variances were analyzed.The results show that shading decreased superoxide anion radical(O-·2)production rate and hydrogen peroxide(H_2O_2) accumulation,kept the activity of SOD,POD and CAT enzyme at a high level.Furthermore,The content of chlorophyll a and chlorophyll b,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),maximal photochemical efficiency of photosystem Ⅱ(Fv/Fm),photochemical quenching index(q P) and effective quantum yield of photosystem II(ΦPSⅡ) of P.cyrtonema were increased while the intercellular CO2 concentration(Ci),Foand NPQ were decreased by shading.Shading is beneficial to P.cyrtonema growth,can increase the total biomass P.cyrtonema.The allocation proportion of biomass on the aerial portion of P.cyrtonema increased but underground parts decreased with increasing shading conditions.In this study,P.cyrtonema can grow well in shading conditions,shading is beneficial to the formation of the yield and quality of the rhizomes of P.cyrtonema,especially in 65% light transmittance.

Unexpected calcium polyhydride CaH4: A possible route to dissociation of hydrogen molecules.

Hydrogen-rich compounds provide an efficient route to pre-compressing hydrogen molecules and facilitating the creation of metallic hydrogen at much reduced pressure. Motivated by the long-sought theoretically proposed calcium hydrides, we have performed high-pressure experiments on the Ca-H system in a laser-heated diamond anvil cell. The unconventional compound CaH4 with I4/mmm symmetry has been discovered to be stable above 25.5 GPa. Of particular significance is the crystal structure of CaH4, which has an elongated H2 molecular unit whose intramolecular bond strength changes with pressure. Below the dissociation pressure of pure hydrogen, the elongated H2 unit is likely to dissociate into an atomic one. Our findings indicate that the presence of Ca atoms causes a very positive chemical pre-compression effect to potentially prompt the dissociation of the H2 unit.

[Effects of N and Zn interaction on growth, yield and active components of Agastache rugosa].

The study is aimed to explore the effect of combination use of nitrogen(N) and zinc(Zn) fertilizers on the growth, yield and the effective components of Agastache rugosa. A. rugosa was grown under two N application rate (120, 300 kg·hm⁻²) and five Zn levels (0, 20, 50, 100，150 kg·hm⁻²) under field condition. The effect of the treatments on the physiological indicators, distribution of nitrogen and zinc and volatile oil components of A. rugosa were studied. The results showed that the combination use of N and Zn could significantly affect the growth and development, yield and volatile oil components of A. rugosa. Under the test conditions, the highest yield of Agastaches Herba was obtained when 50 kg·hm⁻² of Zn fertilizer was applied with high N application rate of 300 kg·hm⁻². Under the same N application rate, the increase of Zn production was positively correlated with the amount of Zn application in a certain concentration range, but excessive Zn application led to the decrease of yield. With the increase of N application level, the content of Zn also significantly increased. The combination use of N and Zn increased the yield of Agastaches Herba. High level of N application was beneficial to the absorption and accumulation of N and Zn of A. rugosa. Zn fertilizer could also promote the absorption and accumulation of N of A. rugosa. The interaction between N and Zn had significant influence on the main chemical constituents of the volatile oil of A. rugosa. Among the volatile oil chemical constituents of A. rugosa the content of pulegone (34.56%-53.91%) and piperonyl methyl ether (18.86%-42.27%) were much higher. Under the same N application rate, different Zn application rates also had significant effects on the main chemical components of volatile oil.

[Effects of exogenous MeJA, SA and two kinds of endophytic fungi on physiology and total phenols content of seedlings of Bletilla striata].

Tissue culture seedlings of Bletilla striata were treated with MeJA, SA and two kinds of endophytic fungi in order to study the effects of those treatments on the physiology and total phenols content. The method of tissue culture was used to culture seeds into seedlings, and then different treatments were applied on them to observe and measure the changes of physiology and total phenols content. We find that the growth of seedlings treated with SA was poor, which treated with 40 µmol•L⁻¹ MeJA, 50 mL•L⁻¹ Hypocrea koningii and 10 mL•L⁻¹ Trichoderma koningiopsis showed better. The activity of SOD, POD and CAT was at a high level under SA treatment of each concentration. The activity of SOD and POD increased as the rise of MeJA concentration, while CAT was highest at 80 µmol•L⁻¹. The activity of SOD and POD increased with the increasing of the concentration of H. koningii treatment, while CAT reached the highest at 1 mL•L⁻¹. The activity of SOD, POD and CAT increased first and then declined with the concentration of T. koningiopsis increasing, and the highest activity was at 10 mL•L⁻¹. The contents of MDA, soluble protein and proline were increased more or less under the four treatments. The content of polysaccharide was at a high level under 60 µmol•L⁻¹ of MeJA. The total phenols content was at a high level under 40 µmol•L⁻¹ of MeJA, 60 µmol•L⁻¹ of SA, 1 mL•L⁻¹ of H. koningii and 10 mL•L⁻¹ of T. koningiopsis. The results indicated that the addition of exogenous MeJA, SA and endophytic fungi under certain concentrations could improve the resistance of B. striata and increase the content of total phenols at some degree and the trearment of MeJA, H. koningii and T. koningiopsis could promote the growth of seedlings under certain concentrations.