Xingxing Jiang

First-principles materials applications and design of nonlinear optical crystals

With the development of laser technology and related scientific fields, understanding of the structure–property relationships in nonlinear optical (NLO) crystals is becoming more and more important. In this article, first-principles studies based on density functional theory, and their applications to elucidate the microscopic origins of the linear and NLO properties in NLO crystals, are reviewed. The ab initio approaches have the ability to accurately predict the optical properties in NLO crystals, and the developed analysis tools are vital to investigating their intrinsic mechanism. This microscopic understanding has further guided molecular engineering design for NLO crystals with novel structures and properties. It is anticipated that first-principle material approaches will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new NLO crystals with good performance.

Thermoelectric performance of SnS and SnS–SnSe solid solution

Solid solution is a potential way to optimize thermoelectric performance for its low thermal conductivity compared to those of the constituent compounds because of the phonon scattering from disordered atoms. Tin(II) sulfide (SnS) shows analogous band structure and electrical properties with tin selenide (SnSe), which was the motivation for investigating the thermoelectric performance of SnS and SnS–SnSe solid solution system. SnS compound and SnS1−xSex (0 < x < 1) solid solution were fabricated using the melting method and they exhibited anisotropic thermoelectric performance along the parallel and perpendicular to the pressing directions. For the SnS compound, the maximum zT∥ value is 0.19 at 823 K along the parallel to pressing direction, which is higher than that along the perpendicular to the pressing direction (zT⊥ = 0.16). The zT values of SnS0.5Se0.5 and SnS0.2Se0.8 were higher than those of the SnS compound and a maximum zT value of 0.82 was obtained for SnS0.2Se0.8 at 823 K, which is more than four times higher than that of SnS.

Near-Zero Thermal Expansion and High Ultraviolet Transparency in a Borate Crystal of Zn4B6O13

Intrinsic isotropic near-zero thermal expansion is discovered in borate crystal Zn4 B6 O13 with high transparency in the ultraviolet region. First-principles calculations demonstrate that the very low thermal expansion originates mainly from the invariability of the solid [B24 O48 ] truncated octahedra that are fixed by the [Zn4 O13 ] clusters in the ZBO structure.

Effects of the interactions between selenium and phosphorus on the growth and selenium accumulation in rice (Oryza sativa).

The solution culture, paddy soil culture and the simulation experiments in the laboratory were conducted to clarify the interactions between selenium and phosphorus, and its effects on the growth and selenium accumulation in rice. Results revealed that a suitable supply of selenium could promote rice growth and excessive selenium could injure rice plant, causing lower biomass, especially in the roots. The supply of selenite could enhance the selenium contents of rice shoots and roots in solution culture and in soil culture. The selenium concentrations in roots were much higher than those in shoots supplied with the same rates of selenium and phosphorus. The interaction between selenium and phosphorus was evident. When the phosphorus supply increased to meet the needs of plant growth, phosphorus could promote absorption and accumulation of selenium in the shoots. If the phosphorus supply was excessive, phosphorus could inhibit the accumulation of selenium in the shoots at the lower selenite level (2 μmol l−1), but could not at the higher selenite level (10 μmol l−1). With the supply of phosphate increased, the selenium concentrations in the roots decreased significantly at both selenite levels. The presence of phosphate could decrease Se sorption on the soil surface and increase the selenium concentration in the soil solution. The concentrations of selenium in shoots and roots supplied with 0.08 g kg−1 phosphorus were lower than those with no phosphorus supplied. With the increase of phosphorus added to 0.4 g kg−1, the selenium concentration in shoots and roots increased. The effect of phosphorus on the concentration was statistically significant at all three selenium levels.

Sr8MgB18O36: a new alkaline-earth borate with a novel zero-dimensional (B18O36)18- anion ring.

A new polyborate, Sr8MgB18O36, has been synthesized. Its crystal structure was determined from single-crystal X-ray diffraction data, and characterizations were made by differential scanning calorimetry, Fourier transform IR, UV-vis-near-IR diffuse-reflectance, and first-principles calculations. The structure of Sr8MgB18O36 contains a novel isolated anionic group-an 18-membered ring (B18O36)(18-), which is the first found in borates.

A combination of multiple chromophores enhances second-harmonic generation in a nonpolar noncentrosymmetric oxide: CdTeMoO6

Single crystals of CdTeMoO6 have been grown from its stoichiometric melts. CdTeMoO6 is non-hygroscopic and resistant to diluted HNO3 aqua-solution. It is also thermally stable up to 766 °C and thereafter melts congruently. Transmittance spectra of CdTeMoO6 show a broad transmittance window in the range of 345 nm to 5.4 μm. Based upon single-crystal X-ray diffraction analysis, CdTeMoO6 is nonpolar noncentrosymmetric (NCS) and features a neutral layered structure consisting of three types of NCS chromophores, i.e. TeO4 polyhedra with a stereoactive lone pair, distorted MoO4 tetrahedra, and regular CdO4 tetrahedra, the former two being counter-packed and the last one being nonpolar. Such a packing manner of the NCS chromophores is traditionally considered unfavorable to produce strong second-harmonic generation (SHG). However, powder SHG measurements reveal that CdTeMoO6 displays a remarkable SHG effect about 2 times that of polar KTiOPO4 (KTP) at 1.064 μm. The first-principles electronic structure and optical properties calculations have confirmed the presence of a strong SHG effect in CdTeMoO6, and have primarily revealed its origin.

Bandgaps in the deep ultraviolet borate crystals: Prediction and improvement

We identify the microscopic structural origins determining the bandgaps in the deep-ultraviolet borates, and propose an efficient method for the prediction of their bandgaps. This method considers only the chemical bond lengths around oxygen atoms and achieves the very high precision with the relative error <5% typically. Its validity is verified by the first-principles studies, which reveal the strong dependence of bandgaps on the coordination environment around oxygen atoms. Our studies have great implications on the search and design of optoelectronic functional materials with large bandgap.

The role of dipole moment in determining the nonlinear optical behavior of materials: ab initio studies on quaternary molybdenum tellurite crystals

The linear and nonlinear optical (NLO) properties of a series of quaternary molybdenum tellurite crystals are studied using a first-principles computational approach and an empirical dipole model. The calculated second harmonic generation (SHG) coefficients are consistent with the experimental values and the calculations show that their magnitude is independent of the dipole moment. Using a flexible dipole model based on the concept of bond-valence it is shown that the size of the NLO effects is determined by the compliance with the dipole moment in response to external perturbation rather than the intrinsic dipole moment of the structure. The study revises the common belief that SHG effects depend on the dipole moment inherent to the unperturbed structure and will help guide the search for new NLO crystals including those that are not necessarily polar.

Chemical changes in heavy metals in the leachates from Technosols.

A 2 month long column study was conducted to evaluate the mobility of heavy metals eluting from Technosols constituted from sewage sludges (aerobic or anaerobic) (as controls) or a mixture of different types of sewage sludges with green foundry sand (FS) or/and Linz-Donowitz slag (LD). The organic and inorganic wastes were mixed at a ratio of 56:44 (w/w). The mixtures and the controls were moistened to field capacity before adding them to the polypropylene columns (4.5 cm wide and 14 cm long). During the 8-week experimental period, the columns were watered, twice a week, with 100 mL of deionised water. The concentrations of heavy metals (Cu, Zn, Ni, Pb, Cd, and Cr) in the leachates were determined periodically. The concentrations of all the heavy metals were generally higher in the leachates from the Technosols containing anaerobic sewage sludge as a component. The concentration of Cu was strongly dependent on pH and was significantly higher (P<0.05) in the most alkaline leachates (pH>10) than in the other leachates. More Zn was mobilized in the most acidic leachates (pH<6) than in other leachates. The concentration of Ni in 80% of the leachates exceeded the EU drinking water limit for Ni (0.02 mgL(-1)). The concentrations of Pb were lower in the Technosols containing FS. The concentrations of Cd in the leachates from Technosols containing the conditioners were relatively high, while concentrations of Cr were higher in the controls. As far as the potential toxicity of heavy metals is concerned, the combination of aerobic sludge, inorganic conditioners able to buffer the pH to around neutrality, and reactive aluminosilicates, can be regarded as suitable choice for formulating Technosols from wastes.

Isotropic Negative Area Compressibility over Large Pressure Range in Potassium Beryllium Fluoroborate and its Potential Applications in Deep Ultraviolet Region

Isotropic negative area compressibility, which is very rare, is observed in KBBF and the related mechanism is investigated by combined high-pressure X-ray diffraction (XRD) experiments and first-principles calculations. The strong mechanical anisotropy leads to a large Poissons ratio and high figure of merit for the acoustic-optics effect, giving KBBF potential applications as smart strain converters and deep-ultraviolet (DUV) acoustic-optic devices.